The idea of how life originated in the ancient eras of the Earth give us fossil remains of organisms, but they are distributed into separate geological periods extremely uneven.
Geological periods
The era of ancient life on Earth includes 3 stages of the evolution of flora and fauna.
Archean era
Archean era- the oldest era in the history of existence. It began about 4 billion years ago. And the duration is 1 billion years. This is the beginning of the formation of the earth's crust as a result of the activity of volcanoes and air masses, sudden changes in temperature and pressure. The process of destruction of primary mountains and the formation of sedimentary rocks is underway.
The most ancient Archeozoic layers of the earth's crust are represented by highly altered, otherwise metamorphosed, rocks, which is why they do not contain noticeable remains of organisms.
But it is completely wrong on this basis to consider the Archaeozoic a lifeless era: in the Archaeozoic there existed not only bacteria and algae, but also more complex organisms.
Proterozoic era
The first reliable traces of life in the form of extremely rare finds and poor preservation are found in Proterozoic, otherwise - the era of “primary life”. The duration of the Proterozoic era is taken to be about 2 million years
Traces of crawling found in Proterozoic rocks annelids, sponge needles, shells of the simplest forms of brachiopods, arthropod remains.
Brachiopods, distinguished by their exceptional diversity of forms, were widespread in the ancient seas. They are found in sediments of many periods, especially the following, Paleozoic era.
Shell of the brachiopod "Horistites Moskvenzis" (ventral valve)
Only a few species of brachiopods have survived to this day. Most brachiopods had shells with unequal valves: the ventral one, on which they lie or are attached to the seabed with the help of a “leg,” was usually larger than the dorsal one. By this feature, in general, it is not difficult to recognize brachiopods.
The small number of fossil remains in Proterozoic deposits is explained by the destruction of most of them as a result of changes (metamorphization) of the containing rock.
Sediments help judge the extent to which life was represented in the Proterozoic. limestones, which then turned into marble. Limestones obviously owe their origin to a special type of bacteria that produced lime carbonate.
The presence of interlayers in the Proterozoic deposits of Karelia shungite, similar to anthracite coal, suggests that the initial material for its formation was the accumulation of algae and other organic residues.
At this distant time, the ancient land was still not lifeless. Bacteria settled in the vast expanses of the still deserted primary continents. With the participation of these simple organisms, weathering and loosening of the rocks that made up the ancient earth's crust occurred.
According to the assumption of the Russian academician L. S. Berg(1876-1950), who studied how life originated in the ancient eras of the Earth, at that time soils had already begun to form - the basis for the further development of vegetation.
Palaeozoic
Deposits next in time, Paleozoic era, otherwise, the era of “ancient life”, which began about 600 million years ago, differs sharply from the Proterozoic in the abundance and diversity of forms even in the most ancient, Cambrian period.
Based on the study of the remains of organisms, it is possible to reconstruct the following picture of the development of the organic world, characteristic of this era.
There are six periods of the Paleozoic era:
Cambrian period
Cambrian period was described for the first time in England, Cambrian County, where its name came from. During this period, all life was connected with water. These are red and blue-green algae, limestone algae. The algae released free oxygen, which enabled the development of organisms that consumed it.
Close examination of blue-green Cambrian clays, which are clearly visible in deep sections of river valleys near St. Petersburg and especially in the coastal regions of Estonia, made it possible to establish in them (using a microscope) the presence plant spores.
This definitely suggests that some species that existed in bodies of water since the earliest times of the development of life on our planet moved to land approximately 500 million years ago.
Among the organisms that inhabited the most ancient Cambrian reservoirs, invertebrates were exceptionally widespread. Of the invertebrates, in addition to the smallest protozoa - rhizomes, they were widely represented worms, brachiopods and arthropods.
Among arthropods, these are primarily various insects, especially butterflies, beetles, flies, and dragonflies. They appear much later. To the same type of animal world, in addition to insects, also belong arachnids and centipedes.
Among the most ancient arthropods there were especially many trilobites, similar to modern woodlice, only much larger (up to 70 centimeters), and crustacean scorpions, which sometimes reached impressive sizes.
Trilobites - representatives of the animal world of the ancient seas Three lobes are clearly distinguished in the body of a trilobite; it is not for nothing that it is called that: translated from ancient Greek, “trilobos” means three-lobed. Trilobites not only crawled along the bottom and buried themselves in the mud, but could also swim.
Among trilobites, generally small forms predominated.
According to geologists, trilobites - “guiding fossils” - are characteristic of many Paleozoic deposits.
The dominant fossils are those that predominate at a given geological time. The age of the sediments in which they are found is usually easily determined from the leading fossils. Trilobites reached their greatest prosperity during the Ordovician and Silurian periods. They disappeared at the end of the Paleozoic era.
Ordovician period
Ordovician period characterized by a warmer and milder climate, as evidenced by the presence of limestones, shale and sandstones in the rock deposits. At this time, the area of the seas increases significantly.
This promotes the reproduction of large trilobites, from 50 to 70 cm in length. Appear in the seas sea sponges, mollusks, and the first corals.
The first corals Silurian
What did the Earth look like in Silurian? What changes occurred on the primeval continents? Judging by the imprints on clay and other stone material, we can definitely say that at the end of the period the first terrestrial vegetation appeared on the shores of reservoirs.
The first plants of the Silurian period
These were small leafy stems plants, which rather resembled sea brown algae, having neither roots nor leaves. The role of leaves was played by green, successively branching stems.
Psilophyte plants - naked plants The scientific name of these ancient progenitors of all land plants (psilophytes, otherwise “naked plants”, i.e. plants without leaves) conveys them well distinctive features. (Translated from ancient Greek “psilos” means bald, naked, and “phytos” means trunk). Their roots were also undeveloped. Psilophytes grew in marshy, marshy soils. An imprint in the rock (right) and a restored plant (left).
Inhabitants of reservoirs of the Silurian period
From inhabitants maritime Silurian reservoirs It should be noted that, in addition to trilobites, corals And echinoderms - sea lilies, sea urchins and stars.
Sea lily "Acantocrinus rex" The crinoids, the remains of which were found in the sediments, bore very little resemblance to predatory animals. Sea lily "Acantocrinus rex" means "thorny king lily". The first word is formed from two Greek words: “acantha” - a thorny plant and “crinone” - lily, the second Latin word “rex” - king.
Cephalopods and especially brachiopods were represented by a huge number of species. In addition to cephalopods that had an internal shell, like belemnites, cephalopods with external shells were widespread in the most ancient periods of the Earth’s life.
The shape of the shell was straight and bent into a spiral. The sink was successively divided into chambers. The largest outer chamber contained the body of the mollusk, the rest were filled with gas. A tube passed through the chambers - a siphon, which allowed the mollusk to regulate the amount of gas and, depending on this, float or sink to the bottom of the reservoir.
Currently, of these cephalopods, only one boat with a coiled shell has been preserved. Ship, or nautilus, which is the same thing, translated from Latin - inhabitant of the warm sea.
The shells of some Silurian cephalopods, such as orthoceras (translated from ancient Greek as “straight horn”: from the words “ortoe” - straight and “keras” - horn), reached gigantic sizes and looked more like a straight two-meter pole than a horn.
Limestones in which orthoceratites occur are called orthoceratitic limestones. Square slabs of limestone were widely used in pre-revolutionary St. Petersburg for sidewalks, and the characteristic sections of orthoceratite shells were often clearly visible on them.
A remarkable event of the Silurian time was the appearance in fresh and brackish bodies of water of clumsy “ armored fish", which had an external bone shell and a non-ossified internal skeleton.
A cartilaginous cord, the notochord, corresponded to the spinal column. Carapaces did not have jaws or paired fins. They were poor swimmers and therefore stuck more to the bottom; Their food was silt and small organisms.
Panzerfish Pterichthys The armored fish Pterichthys was generally a poor swimmer and led a natural lifestyle.
It can be assumed that Bothriolepis was already much more mobile than Pterichthys.
Sea predators of the Silurian period
In later deposits there are already remains sea predators, close to sharks. From these lower fish, which also had a cartilaginous skeleton, only teeth were preserved. Judging by the size of the teeth, for example from Carboniferous deposits of the Moscow region, we can conclude that these predators reached significant sizes.
In the development of the animal world of our planet, the Silurian period is interesting not only because the distant ancestors of fish appeared in its reservoirs. At the same time, another equally important event took place: representatives of arachnids climbed out of the water onto land, among them ancient scorpions, still very close to crustaceans.
Cancer scorpions are inhabitants of shallow seas On the right, at the top is a predator armed with strange claws - Pterygotus, reaching 3 meters, glory - Eurypterus - up to 1 meter long.
Devonian
The land - the arena of the future life - gradually takes on new features, especially characteristic of the next, Devonian period. At this time, woody vegetation appears, first in the form of low-growing shrubs and small trees, and then larger ones. Among the Devonian vegetation we will meet well-known ferns, other plants will remind us of the graceful fir-tree of horsetail and the green ropes of club mosses, only not creeping along the ground, but proudly rising upward.
In later Devonian deposits, fern-like plants also appear, which reproduced not by spores, but by seeds. These are seed ferns, occupying a transitional position between spore and seed plants.
Fauna of the Devonian period
Animal world seas Devonian period rich in brachiopods, corals and crinoids; trilobites begin to play a secondary role.
Among cephalopods, new forms appear, only not with a straight shell, like in Orthoceras, but with a spirally twisted one. They are called ammonites. They received their name from the Egyptian sun god Ammon, near the ruins of whose temple in Libya (Africa) these characteristic fossils were first discovered.
By general appearance they are difficult to confuse with other fossils, but at the same time it is necessary to warn young geologists about how difficult it can be to identify individual species of ammonites, the total number of which is not in the hundreds, but in the thousands.
Ammonites reached a particularly magnificent flourishing in the next, Mesozoic era. .
Fish developed significantly in Devonian times. In armored fish, the bony shell was shortened, which made them more mobile.
Some armored fish, such as the nine-meter giant Dinichthys, were terrible predators (in Greek “deinos” means terrible, terrible, and “ichthys” means fish).
The nine-meter-long dinychthys obviously posed a great threat to the inhabitants of reservoirs.
In Devonian reservoirs there were also lobe-finned fish, from which lungfish evolved. This name is explained by the structural features of the paired fins: they are narrow and, in addition, sit on an axis covered with scales. This feature distinguishes lobe-finned fish, for example, from pike-perch, perch and other bony fish called ray-finned fish.
Lobe-finned fish are the ancestors of bony fish, which appeared much later - at the end of the Triassic.
We would have no idea what lobe-finned fish that lived at least 300 million years ago actually looked like if it weren’t for the successful catches of the rarest specimens of their modern generation in the mid-twentieth century off the coast of South Africa.
They apparently live at considerable depths, which is why they are so rarely seen by fishermen. The caught species was named coelacanth. It reached 1.5 meters in length.
In their organization, lungfishes are close to lobe-finned fish. They have lungs corresponding to the swim bladder of a fish.
In their organization, lungfishes are close to lobe-finned fish. They have lungs corresponding to the swim bladder of a fish.
How unusual the lobe-finned fish looked can be judged by a specimen, a coelacanth, caught in 1952 off the Comoros Islands, west of the island of Madagascar. This 1.5 liter long fish weighed about 50 kg.
A descendant of ancient lungfishes, the Australian ceratodus (translated from ancient Greek as horntooth) reaches two meters. It lives in drying up reservoirs and, as long as there is water in them, breathes with gills, like all fish, but when the reservoir begins to dry out, it switches to pulmonary respiration.
Australian ceratodus - a descendant of ancient lungfish Its respiratory organs are the swim bladder, which has a cellular structure and is equipped with numerous blood vessels. In addition to Ceratodus, two more species of lungfish are now known. One of them lives in Africa, and the other in South America.
Transition of vertebrates from water to land
Amphibian transformation table.
The oldest fish 
The first picture shows the oldest cartilaginous fish, Diplocanthus (1). Below it is a primitive lobe-finned eusthenopteron (2); below is a supposed transitional form (3). The huge amphibian Eogyrinus (about 4.5 m in length) has limbs that are still very weak (4), and only as they master the land way of life do they become a reliable support, for example, for the heavy Eryops, about 1.5 m in length (5).
This table helps to understand how, as a result of gradual changes in the organs of locomotion (and breathing), aquatic organisms moved to land, how the fin of a fish was transformed into the limb of amphibians (4), and then reptiles (5). At the same time, the spine and skull of the animal change.
The Devonian period dates back to the appearance of the first wingless insects and terrestrial vertebrates. From this we can assume that it was at this time, and perhaps even a little earlier, that the transition of vertebrates from water to land took place.
It was realized through fish in which the swim bladder was modified, like in lungfishes, and the fin-like limbs gradually turned into five-fingered ones, adapted to a terrestrial lifestyle.
Metopoposaurus still had difficulty getting onto land.
Therefore, the closest ancestors of the first land animals should therefore be considered not lungfish, but lobe-finned fish, which adapted to breathing atmospheric air as a result of periodic drying out of tropical reservoirs.
The link between terrestrial vertebrates and lobe-finned animals are ancient amphibians, or amphibians, collectively called stegocephalians. Translated from ancient Greek, stegocephaly means “covered-headed”: from the words “stege” - roof and “mullet” - head. This name is given because the roof of the skull is a rough shell of bones closely adjacent to each other.
There are five holes in the stegocephalus skull: two pairs of holes - ophthalmic and nasal, and one for the parietal eye. By appearance stegocephalians somewhat resembled salamanders and often reached considerable sizes. They lived in swampy areas.
The remains of stegocephals were sometimes found in hollows of tree trunks, where they apparently hid from daylight. In the larval state, they breathed through gills, just like modern amphibians.
Stegocephals found especially favorable conditions for their development in the next Carboniferous period.
Carboniferous period
Warm and humid climate, especially in the first half Carboniferous period, favored the lush flourishing of terrestrial vegetation. The coal forests, never seen by anyone, were, of course, completely different from those of today.
Among those plants that settled in marshy, marshy areas approximately 275 million years ago, giant tree-like horsetails and club mosses clearly stood out in their characteristic features.
Of the tree-like horsetails, calamites were widely used, and of the clubmosses, giant lepidodendrons and, somewhat smaller in size, graceful sigillaria.
In coal seams and the rocks covering them, well-preserved remains of vegetation are often found, not only in the form of clear imprints of leaves and tree bark, but also entire stumps with roots and huge trunks that have turned into coal.
Using these fossil remains, you can not only reconstruct the general appearance of the plant, but also get acquainted with its internal structure, which is clearly visible under a microscope in paper-thin sections of the trunk. Calamites get their name from the Latin word “calamus” - reed, reed.
The slender, hollow inside trunks of the calamites, ribbed and with transverse constrictions, like those of the well-known horsetails, rose in slender columns 20-30 meters from the ground.
Small narrow leaves, collected in rosettes on short stems, gave, perhaps, some resemblance to calamite with the larch of the Siberian taiga, transparent in its elegant decoration.
Nowadays, horsetails - field and forest - are distributed throughout the globe, except Australia. In comparison with their distant ancestors, they seem pitiful dwarfs, which, moreover, especially horsetail, have a bad reputation among farmers.
Horsetail is a nasty weed that is difficult to control, since its rhizome goes deep into the ground and continually produces new shoots.
Large species of horsetails - up to 10 meters in height - are currently preserved only in the tropical forests of South America. However, these giants can only grow by leaning against neighboring trees, since they are only 2-3 centimeters in diameter.
Lepidodendrons and sigillaria occupied a prominent place among the Carboniferous vegetation.
Although they were not similar in appearance to modern mosses, they still resembled them in one characteristic feature. The powerful trunks of lepidodendrons, reaching 40 meters in height and up to two meters in diameter, were covered with a distinct pattern of fallen leaves.
These leaves, while the plant was still young, sat on the trunk in the same way as its small green scales - leaves - sit on the club moss. As the tree grew, the leaves aged and fell off. From these scaly leaves, the giants of the coal forests got their name - lepidodendrons, otherwise - “scaly trees” (from the Greek words: “lepis” - scales and “dendron” - tree).
The traces of fallen leaves on the bark of the sigillaria had a slightly different shape. They differed from lepidodendrons in their smaller height and more slender trunk, which branched only at the very top and ended in two huge bunches of hard leaves, each about a meter long.
An introduction to Carboniferous vegetation would be incomplete without also mentioning cordaites, which are close to conifers in wood structure. These were tall (up to 30 meters), but relatively thin-trunked trees.
Cordaites get their name from the Latin elephant “cor” - heart, since the seed of the plant was heart-shaped. These beautiful trees were crowned with a lush crown of ribbon-like leaves (up to 1 meter in length).
Judging by the structure of the wood, the trunks of the coal giants still did not have the strength that is generally inherent in modern trees. Their bark was much stronger than wood, hence the general fragility of the plant and weak resistance to fracture.
Strong winds and especially storms broke trees, felled huge forests, and in their place again new lush growth grew from the swampy soil... The felled wood served as the source material from which powerful layers of coal were subsequently formed.
Lepidodendrons, otherwise known as scaly trees, reached enormous sizes.
It is not correct to attribute the formation of coal only to the Carboniferous period, since coals also occur in other geological systems.
For example, the oldest Donetsk coal basin was formed during the Carboniferous era. The Karaganda pool is the same age as it.
As for the largest Kuznetsk basin, only a small part of it belongs to the Carboniferous system, and mainly to the Permian and Jurassic systems.
One of the largest basins - the “Polar Stoker” - the richest Pechora basin, was also formed mainly in the Permian period and, to a lesser extent, in the Carboniferous period.
Flora and fauna of the Carboniferous period
For marine sediments Carboniferous period Representatives of the simplest animals from the class are especially characteristic rhizomes. The most typical were fusulines (from the Latin word “fusus” - “spindle”) and schwagerins, which served as the starting material for the formation of strata of fusuline and schwagerin limestones.
Carboniferous rhizomes: 1 - fusulina; 2 - schwagerina Carboniferous rhizomes - fusulin (1) and schwagerina (2) are enlarged 16 times.
Elongated, like grains of wheat, fusulines and almost spherical schwagerins are clearly visible on the limestones of the same name. Corals and brachiopods developed magnificently, giving rise to many leading forms.
The most widespread were the genus productus (translated from Latin - “stretched”) and spirifer (translated from the same language - “bearing spiral”, which supported the soft “legs” of the animal).
Trilobites, which dominated in previous periods, are found much less frequently, but on land other representatives of arthropods are beginning to become noticeably widespread - long-legged spiders, scorpions, huge centipedes (up to 75 centimeters in length) and especially gigantic insects, similar to dragonflies, with a wingspan. up to 75 centimeters! The largest modern butterflies in New Guinea and Australia reach a wingspan of 26 centimeters.
The oldest Carboniferous dragonfly The ancient Carboniferous dragonfly seems like an enormous giant compared to the modern one.
Judging by the fossil remains, sharks have noticeably multiplied in the seas.
Amphibians, firmly established on land during Carboniferous times, go through a further development path. The dry climate, which increased at the end of the Carboniferous period, gradually forced ancient amphibians to move away from an aquatic lifestyle and move primarily to a terrestrial existence.
These organisms, transitional to a new way of life, laid eggs on land, and did not spawn in the water, like amphibians. The offspring hatched from the eggs acquired characteristics that sharply distinguished them from their ancestors.
The body was covered, like a shell, with scale-like outgrowths of the skin, protecting the body from loss of moisture through evaporation. So reptiles, or reptiles, separated from amphibians (amphibians). In the next Mesozoic era, they conquered land, water and air.
Permian period
Last Paleozoic period - Permian- was significantly shorter in duration than the Carboniferous. It should be noted, in addition, the great changes that have occurred on the ancient geographical map of the world - land, as confirmed by geological research, gains significant dominance over the sea.
Plants of the Permian period
The climate of the northern continents of the Upper Permian was dry and sharply continental. Sandy deserts have become widespread in some places, as evidenced by the composition and reddish tint of the rocks that make up the Permian formation.
This time was marked by the gradual extinction of the giants of the coal forests, the development of plants close to conifers, and the appearance of cycads and ginkgos, which became widespread in the Mesozoic.
Cycad plants have a spherical and tuberous stem immersed in the soil, or, conversely, a powerful columnar trunk up to 20 meters high, with a lush rosette of large feathery leaves. In appearance, cycad plants resemble the modern sago palm of tropical forests in the Old and New Worlds.
Sometimes they form impenetrable thickets, especially on the flooded banks of the rivers of New Guinea and the Malay Archipelago (Great Sunda Islands, Lesser Sunda Islands, Moluccas and Philippine Islands). Nutritious flour and cereals (sago) are made from the soft pith of the palm tree, which contains starch.
Forest of sigillaries Sago bread and porridge are the daily food of millions of inhabitants of the Malay Archipelago. Sago palm is widely used in housing construction and household products.
Another very peculiar plant, ginkgo, is also interesting because it has survived in the wild only in some places in Southern China. Ginkgo has been carefully cultivated near Buddhist temples since time immemorial.
Ginkgo was brought to Europe in the mid-18th century. Now it is found in park culture in many places, including here on the Black Sea coast. Ginkgo is a large tree up to 30-40 meters in height and up to two meters thick, in general it resembles a poplar, but in its youth it is more like some conifers.
Branch of modern Ginkgo biloba with fruits The leaves are petiolate, like those of aspen, have a fan-shaped plate with fan-shaped venation without transverse bridges and a notch in the middle. In winter the leaves fall off. The fruit, a fragrant drupe like a cherry, is edible in the same way as the seeds. In Europe and Siberia, ginkgo disappeared during the Ice Age.
Cordaites, conifers, cycads and ginkgo belong to the group of gymnosperms (since their seeds lie open).
Angiosperms - monocotyledons and dicotyledons - appear somewhat later.
Fauna of the Permian period
Among the aquatic organisms that inhabited the Permian seas, ammonites stood out noticeably. Many groups of marine invertebrates, such as trilobites, some corals and most brachiopods, became extinct.
Permian period characteristic of the development of reptiles. The so-called bestial lizards deserve special attention. Although they possessed some features characteristic of mammals, such as teeth and skeletal features, they still retained a primitive structure that brought them closer to stegocephals (from which reptiles originated).
The beast-like Permian lizards were distinguished by their considerable size. The sedentary herbivorous pareiasaurus reached two and a half meters in length, and the formidable predator with tiger teeth, otherwise known as the “animal-toothed lizard” - inostrantseviya, was even larger - about three meters.
Pareiasaurus translated from ancient Greek means “cheeked lizard”: from the words “pareia” - cheek and “sauros” - lizard, lizard; The wild-toothed lizard Inostracevia is named so in memory of the famous geologist - prof. A. A. Inostrantseva (1843-1919).
The richest finds from the ancient life of the Earth, the remains of these animals, are associated with the name of the enthusiastic geologist Prof. V. P. Amalitsky(1860-1917). This persistent researcher, without receiving the necessary support from the treasury, nevertheless achieved remarkable results in his work. Instead of a well-deserved summer rest, he and his wife, who shared all the hardships with him, went in a boat with two oarsmen in search of the remains of bestial lizards.
Persistently, for four years he conducted his research on the Sukhona, Northern Dvina and other rivers. Finally, he managed to make discoveries that were extremely valuable for world science on the Northern Dvina, not far from the city of Kotlas.
Here, in the coastal cliff of the river, concretions of the bones of ancient animals (concretions - stone accumulations) were discovered in thick lentils of sand and sandstone, among striped rudders. The collection of just one year of work by geologists took two freight cars during transportation.
Subsequent developments of these bone-bearing accumulations further enriched the information about Permian reptiles.
Place of finds of Permian dinosaurs Place of finds of Permian dinosaurs discovered by the professor V. P. Amalitsky in 1897. The right bank of the Malaya Northern Dvina River near the village of Efimovka, near the city of Kotlas.
The richest collections taken from here amount to tens of tons, and the skeletons collected from them represent in the Paleontological Museum of the Academy of Sciences a rich collection, which has no equal in any museum in the world.
Among the ancient animal-like Perm reptiles, the original three-meter predator Dimetrodon stood out, otherwise “two-dimensional” in length and height (from the ancient Greek words: “di” - twice and “metron” - measure).
Beastlike Dimetrodon Its characteristic feature is the unusually long processes of the vertebrae, forming a high ridge on the animal’s back (up to 80 centimeters), apparently connected by a skin membrane. In addition to predators, this group of reptiles also included plant- or molluscivorous forms, also of very significant size. The fact that they ate shellfish can be judged by the structure of their teeth, suitable for crushing and grinding shells. (No ratings yet)
Archean era. The beginning of this ancient era is considered not the moment of the formation of the Earth, but the time after the formation of the solid earth's crust, when mountains and rocks already existed and the processes of erosion and sedimentation began to take effect. The duration of this era is approximately 2 billion years, i.e. it corresponds to all other eras combined. The Archean era appears to have been characterized by catastrophic and widespread volcanic activity, as well as deep uplifts that culminated in the formation of mountains. The high temperature, pressure and mass movements that accompanied these movements apparently destroyed most of the fossils, but some data about life of those times still remained. In Archeozoic rocks, graphite or pure carbon is found everywhere in scattered form, which probably represents the altered remains of animals and plants. If we accept that the amount of graphite in these rocks reflects the amount of living matter (and this, apparently, is the case), then in the Archean there was probably a lot of this living matter, since there is more carbon in rocks of this age than in coal seams of the Appalachian Basin.
Proterozoic era. The second era, lasting about 1 billion years, was characterized by the deposition of large amounts of sediment and at least one significant glaciation, during which ice sheets extended to latitudes less than 20° from the equator. A very small number of fossils have been found in Proterozoic rocks, which, however, indicate not only the existence of life in this era, but also that evolutionary development had advanced far towards the end of the Proterozoic. Sponge spicules, remains of jellyfish, fungi, algae, brachiopods, arthropods, etc. were found in Proterozoic deposits.
Palaeozoic. Between the deposits of the Upper Proterozoic and the initial layers of the third, Paleozoic era, there is a significant break caused by mountain-building movements. Over 370 million years of the Paleozoic era, representatives of all types and classes of animals appeared, with the exception of birds and mammals. Because different types of animals existed only for certain periods of time, their fossil remains allow geologists to compare sediments of the same age that occur in different places.
- Cambrian period [show]
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Cambrian period- the most ancient department of the Paleozoic era; is represented by rocks replete with fossils, so that the appearance of the Earth at this time can be reconstructed quite accurately. The forms that lived during this period were so diverse and complex that they must have descended from ancestors that existed at least in the Proterozoic, and possibly in the Archean.
All modern types of animals, with the exception of chordates, already existed and all plants and animals lived in the sea (the continents, apparently, were lifeless deserts until the late Ordovician or Silurian, when plants moved to land). There were primitive, shrimp-like crustaceans and arachnid-like forms; some of their descendants have survived, almost unchanged, to this day (horseshoe crabs). The seabed was covered with solitary sponges, corals, stalked echinoderms, gastropods and bivalves, primitive cephalopods, brachiopods and trilobites.
Brachiopods, sessile animals that have bivalve shells and feed on plankton, flourished in the Cambrian and in all other systems of the Paleozoic.
Trilobites are primitive arthropods with an elongated flat body covered on the dorsal side with a hard shell. Two grooves stretch along the shell, dividing the body into three parts, or lobes. Each body segment, with the exception of the very last, bears a pair of two-branched limbs; one of them was used for walking or swimming and had a gill on it. Most trilobites were 5-7.5 cm in length, but some reached 60 cm.
In the Cambrian, both unicellular and multicellular algae existed. One of the best preserved collections of Cambrian fossils was collected in the mountains of British Columbia. It includes worms, crustaceans and a transitional form between worms and arthropods, similar to the living Peripatus.
After the Cambrian, evolution was characterized mainly not by the emergence of completely new types of structure, but by the branching of existing lines of development and the replacement of the original primitive forms with more highly organized ones. Probably, the already existing forms reached such a degree of adaptation to environmental conditions that they acquired a significant advantage over any new, unadapted types.
- Ordovician period [show]
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During the Cambrian period, the continents began to gradually submerge in water, and in the Ordovician period this subsidence reached its maximum, so that much of the present landmass was covered by shallow seas. These seas were inhabited by huge cephalopods - animals similar to squid and nautilus - with a straight shell from 4.5 to 6 m long and 30 cm in diameter.
The Ordovician seas were apparently very warm, since corals, which live only in warm waters, spread at this time as far as Lake Ontario and Greenland.
The first remains of vertebrates were found in Ordovician deposits. These small animals, called scutes, were bottom-dwelling forms, lacking jaws and paired fins (Fig. 1.). Their shell consisted of heavy bony plates on the head and thick scales on the body and tail. Otherwise they were similar to modern lampreys. They apparently lived in fresh water, and their shell served as protection from giant predatory aquatic scorpions called eurypterids, which also lived in fresh water.
- Silurian [show]
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The Silurian period saw two events of great biological significance: the development of land plants and the appearance of air-breathing animals.
The first land plants were apparently more similar to ferns than to mosses; Ferns were also the dominant plants in the subsequent Devonian and lower Carboniferous periods.
The first air-breathing land animals were arachnids, somewhat reminiscent of modern scorpions.
Continents that had been low-lying in Cambrian and Ordovician times rose, especially in Scotland and northeastern North America, and the climate became much cooler.
- Devonian [show]
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During the Devonian, the first armored fish gave rise to many different fish, so that this period is often called the “time of the fish.”
Jaws and paired fins first evolved in armored sharks (Placodermi), which were small, shell-covered freshwater forms. These animals were characterized by a variable number of paired fins. Some had two pairs of fins, corresponding to the fore and hind limbs of higher animals, while others had up to five pairs of additional fins between these two pairs.
During the Devonian, true sharks appeared in fresh waters, which showed a tendency to move to the ocean and lose their bulky bony shell.
The ancestors of bony fishes also arose in Devonian freshwater streams; by the middle of this period, they developed a division into three main types: lungfish, lobe-finned and ray-finned. All these fish had lungs and a shell of bony scales. Only a very few lungfishes have survived to this day, and the ray-finned fishes, having undergone a period of slow evolution throughout the remainder of the Paleozoic era and the beginning of the Mesozoic, later, in the Mesozoic, experienced significant divergence and gave rise to modern bony fishes (Teleostei).
Lobe-finned fish, which were the ancestors of land vertebrates, almost became extinct by the end of the Paleozoic and, as previously believed, completely disappeared at the end of the Mesozoic. However, in 1939 and 1952. Live representatives of lobe-fins, about 1.5 m long, were caught off the east coast of South Africa.
The upper Devonian was marked by the appearance of the first land vertebrates - amphibians called stegocephalians (meaning "covered-headed"). These animals, whose skulls were covered with a bony shell, are in many respects similar to lobe-finned fish, differing from them mainly in the presence of limbs rather than fins.
The Devonian is the first period characterized by real forests. During this period, ferns, club mosses, pteridophytes and primitive gymnosperms - the so-called "seed ferns" - flourished. It is believed that insects and millipedes arose in late Devonian times.
- Carboniferous period [show]
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At this time, large swamp forests were widespread, the remains of which gave rise to the main coal deposits of the world. The continents were covered with low-lying swamps, overgrown with pteridophytes, common ferns, seed ferns and broad-leaved evergreens.
The first reptiles, called whole-skulled and similar to the amphibians that preceded them, appeared in the second half of the Carboniferous period, reached their peak in the Permian - the last period of the Paleozoic - and died out at the beginning of the Mesozoic era. It is not clear whether the most primitive reptile known to us, Seymouria (named after the city in Texas near which its fossil remains were found), was an amphibian ready to turn into a reptile, or a reptile that had just crossed the border separating it from amphibians .
One of the main differences between amphibians and reptiles is the structure of the eggs they lay. Amphibians lay their eggs, covered with a gelatinous shell, in water, and reptiles lay their eggs, covered with a durable shell, on the ground. Since the eggs of Seymouria have not been preserved, we may never be able to decide to what class this animal should be placed.
Seymouria was a large, slow-moving, lizard-like form. Its short, stump-like legs extended away from its body in a horizontal direction, like a salamander's, instead of being tightly packed and going straight down, forming column-like supports for the body.
During the Carboniferous period, two important groups of winged insects appeared - the ancestors of cockroaches, which reached 10 cm in length, and the ancestors of dragonflies, some of which had a wingspan of 75 cm.
- Permian period [show]
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The last period of the Paleozoic was characterized by major changes in climate and topography. Continents rose all over the globe, so that the shallow seas that covered the area from Nebraska to Texas dried up, leaving behind a saline desert. At the end of the Permian, widespread folding occurred, known as the Hercynian orogeny, during which a large mountain range rose from Nova Scotia to Alabama. This range was originally higher than the modern Rocky Mountains. At the same time, other mountain ranges were forming in Europe.
Huge ice sheets spreading from the Antarctic covered most of the southern hemisphere, extending in Africa and Brazil almost to the equator.
North America was one of the few areas not subject to glaciation at this time, but even here the climate became significantly colder and drier than it had been during most of the Paleozoic era. Many Paleozoic organisms apparently could not adapt to climate change and became extinct during the Hercynian orogeny. Due to the cooling of water and the reduction of space suitable for life as a result of the drying out of shallow seas, even many marine forms became extinct.
From primitive whole-skulled animals, during the Late Carboniferous and Early Permian times, that group of reptiles developed, from which mammals are believed to have descended in a direct line. These were pelycosaurs - predatory reptiles with a more slender and lizard-like body than those of whole skulls.
In the Late Permian time, another group of reptiles, the therapsids, developed, probably from pelycosaurs, and had several more characteristics of mammals. One of the representatives of this group, Cynognathus (the “dog-jawed” reptile), was a slender, light animal about 1.5 m long, with a skull intermediate in character between that of a reptile and a mammal. Its teeth, instead of being conical and uniform, as is typical of reptiles, were differentiated into incisors, canines and molars. Since we have no information about the soft parts of the animal, whether it was covered with scales or hair, whether it was warm-blooded or cold-blooded, and whether it suckled its young, we call it a reptile. However, if we had more complete data, it might be considered a very early mammal. Therapsids, widespread in the late Permian, were replaced by many other reptiles at the beginning of the Mesozoic.
Mesozoic era (time of reptiles). The Mesozoic era, which began approximately 230 million years ago and lasted about 167 million years, is divided into three periods:
- Triassic
- Jurassic
- chalky
During the Triassic and Jurassic periods, most of the continental areas were raised above sea level. In the Triassic the climate was dry, but warmer than in the Permian, and in the Jurassic it was warmer and more humid than in the Triassic. The trees of Arizona's famous Stone Forest have been around since the Triassic period.
During the Cretaceous period, the Gulf of Mexico expanded and flooded Texas and New Mexico, and in general the sea gradually advanced onto the continents. In addition, extensive swamps have developed in an area stretching from Colorado to British Columbia. At the end of the Cretaceous period, the interior of the North American continent experienced further subsidence, so that the waters of the Gulf of Mexico basin connected with the waters of the Arctic basin and divided this continent into two parts. The Cretaceous period ended with a large uplift called the Alpine orogeny, during which the Rocky Mountains, Alps, Himalayas and Andes were created and which caused active volcanic activity in western North America.
Evolution of reptiles . The emergence, differentiation and finally extinction of a great variety of reptiles belonging to six main branches is the most characteristic feature of the Mesozoic era [show] .
The most primitive branch includes, in addition to the ancient whole-skulls, turtles that arose in the Permian. Turtles have developed the most complex shell (among terrestrial animals); it consists of plates of epidermal origin fused with the underlying ribs and sternum. With this protective adaptation, both sea and land turtles have survived from pre-dinosaur times with few structural changes. The legs of turtles, extending from the body in a horizontal direction, which complicates and slows down movement, and their skulls, which do not have holes behind the eye sockets, were inherited from ancient whole-skulls without changes.
The second group of reptiles, which comes with relatively few changes from the ancestral whole-skulled ones, are lizards, the most numerous among living reptiles, as well as snakes. Lizards for the most part have retained a primitive type of movement using horizontally diverging legs, although many of them can run quickly. In most cases they are small, but the Indian monitor reaches 3.6 m in length, and some fossil forms are 7.5 m in length. Mosasaurs of the Cretaceous period were sea lizards that reached 12 m in length; they had a long tail, used for swimming.
During the Cretaceous period, snakes evolved from lizard ancestors. The significant difference between snakes and lizards is not the loss of legs (some lizards also lack legs), but certain changes in the structure of the skull and jaws that allow snakes to open their mouths wide enough to swallow animals larger than themselves.
A representative of an ancient branch that somehow managed to survive to this day in New Zealand is the hatteria (Shpenodon punctatum). It shares several features with its cotylosaurian ancestors; one such sign is the presence of a third eye at the top of the skull.
The main group of Mesozoic reptiles were archosaurs, the only living representatives of which are alligators and crocodiles. At some early point in their evolution, archosaurs, then reaching 1.5 m in length, adapted to walking on two legs. Their front legs shortened, while their hind legs lengthened, became stronger, and greatly changed their shape. These animals rested and walked on all four legs, but in critical circumstances they reared and ran on their two hind legs, using their rather long tail as a balance.
Early archosaurs evolved into many different specialized forms, with some continuing to walk on two legs and others returning to walking on all fours. These descendants include phytosaurs - aquatic, alligator-like reptiles common in the Triassic; crocodiles, which formed in the Jurassic and replaced phytosaurs as aquatic forms, and finally pterosaurs, or flying reptiles, which included animals the size of a robin, as well as the largest animal ever to fly, Pteranodon, with a wingspan of 8 m.
There were two types of flying reptiles; some had a long tail equipped with a steering blade at the end, others had a short tail. Representatives of both types apparently fed on fish and probably flew long distances over water in search of food. Their legs were not adapted for standing, and therefore it is assumed that, like bats, they rested in a suspended state, clinging to some support.
Of all the branches of reptiles, the most famous are dinosaurs, which translated means “terrible lizards.” They were divided into two main types: ornithischians and saurians.
Saurischia (lizard-hipped) first appeared in the Triassic and continued to exist until the Cretaceous. Early lizards were fast, predatory, bipedal, rooster-sized forms that likely preyed on lizards and the primitive mammals that had already emerged. During the Jurassic and Cretaceous periods, this group showed a tendency to increase in size, reaching its highest expression in the giant Cretaceous predator Tyrannosaurus. Other Saurischia, which appeared in Late Triassic times, switched to a plant diet, again began to walk on four legs, and during the Jurassic and Cretaceous gave rise to a number of giant forms that led an amphibious lifestyle. These largest four-legged animals that ever lived include brontosaurus, up to 20 m long, diplodocus, which reached a length of over 25 m, and brachiosaurus, the largest of all, whose weight is estimated at 50 tons.
Another group of dinosaurs, the Ornitischia (ornithischians), were herbivores probably from the very beginning of their evolution. Although some walked on their hind legs, most walked on all four legs. Instead of missing front teeth, they developed a strong horny sheath, similar to a bird's beak, which in some forms was wide and flat, like a duck's (hence the name "duck-billed" dinosaurs). This type is characterized by webbed feet. Other species developed large armor plates that protected them from predatory lizards. The ankylosaur, which is called a “tank reptile,” had a wide, flat body covered with bony plates and large spines protruding from its sides.
Finally, some Cretaceous ornithischians developed bony plates around the head and neck. One of them, Triceratops, had two horns over the eyes and a third over the nasal area - all up to almost 1 m long.
Two other groups of Mesozoic reptiles that differed both from each other and from dinosaurs were the marine plesiosaurs and ichthyosaurs. The first were characterized by an extremely long neck, accounting for more than half the length of the animal. Their body was wide, flat, resembling the body of a turtle, and their tail was short. Plesiosaurs swam with flipper-like limbs. They often reached 13-14 m in length.
Ichthyosaurs (fish lizards) were similar in appearance to fish or whales, with a short neck, a large dorsal fin and a shark-like tail. They swam using rapid movements of their tails, using their limbs only as controls. It is believed that ichthyosaur cubs were born alive, hatching from an egg in the mother’s body, since adult individuals were too specialized and could not go onto land to lay eggs, and reptile eggs drown in water. The discovery of baby skeletons inside the abdominal cavity of adult fossils supports this theory.
At the end of the Cretaceous, many reptiles became extinct. They obviously could not adapt to the significant changes in environmental conditions caused by the Alpine orogeny. As the climate became colder and drier, many plants that served as food for herbivorous reptiles disappeared. Some herbivorous reptiles were too cumbersome to move on land when the swamps dried up. The smaller, warm-blooded mammals that had already appeared had an advantage in the competition for food, and many of them even fed on reptile eggs. The extinction of many reptiles was probably the result of the combined influence of a number of factors or of a single factor.
Other directions of evolution in the Mesozoic . Although reptiles were the dominant animals in the Mesozoic, many other important organisms also evolved during this time. [show] .
During the Mesozoic, the number and diversity of gastropods and bivalves increased. Sea urchins have reached highest point of its development.
Mammals arose in the Triassic, and bony fish and birds appeared in the Jurassic.
Most modern insect orders appeared in the early Mesozoic.
During Early Triassic time, the most common plants were seed ferns, cycads and conifers, but by the Cretaceous period many other forms resembling modern species appeared - fig trees, magnolias, palms, maples and oaks.
From the Jurassic time, magnificent prints of the very ancient looking birds on which even the outlines of feathers are visible. This creature, called Archeopteryx, was about the size of a crow and had rather weak wings, armed with jaw teeth and a long, reptilian tail covered with feathers.
Fossils of two other birds were found in the Cretaceous deposits - Hesperornis and Ichthyornis. The first is an aquatic diving bird that has lost the ability to fly, and the second is a strong flying bird with reptilian teeth, about the size of a dove.
Modern toothless birds formed at the beginning of the next era.
Cenozoic era (time of mammals). The Cenozoic era can equally rightly be called the time of birds, the time of insects or the time of flowering plants, since the development of all these organisms is no less characteristic of it than the development of mammals. It covers the period from the Alpine mountain formation (about 63 million years ago) to the present day and is divided into two periods - the Tertiary, which lasted about 62 million years, and the Quaternary, which includes the last 1-1.5 million years.
- Tertiary period. This period is divided into five eras: Paleocene, Eocene, Oligocene, Miocene and Pliocene. The rocky mountains, formed at the beginning of the Tertiary period, were already heavily eroded by the Oligocene time, as a result of which the North American continent acquired a gently undulating topography.
During the Miocene, another series of uplifts created the Sierra Nevada and new ranges in the Rocky Mountains, which created deserts in the west. The climate in the Oligocene was milder than today, so palms spread as far north as Wyoming.
The uplift, which began in the Miocene, continued into the Pliocene and, combined with the glaciations of Pleistocene time, led to the extinction of many pre-existing mammals and other animals. The final uplift of the Colorado Plateau, which created the Grand Canyon, was almost completed in the short time of the Pleistocene and modern eras.
The oldest fossil remains of true mammals date back to the Late Triassic, and in Jurassic times there were already four orders of mammals, all of them the size of a rat or a small dog.
The oldest mammals (monotremes) were oviparous animals, and their only representatives that have survived to this day are the platypus and the spiny echidna living in Australia. Both of these forms have fur and nurse their young with milk, but they also lay eggs, like turtles. The ancestral oviparous mammals must, of course, have been distinct from the specialized platypus and echidna, but the fossil record of these ancient forms is incomplete. Today's living monotremes could survive for so long only because they lived in Australia, where until recently there were no placental mammals, so they had no one to compete with.
In the Jurassic and Cretaceous, most mammals were already highly enough organized to produce live young, although in the most primitive of them - marsupials - the young are born underdeveloped and must remain for several months in a pouch on the mother's stomach, where the nipples are located. Australian marsupials, like monotremes, did not encounter competition from more adapted placental mammals, while on other continents this competition led to the extinction of marsupials and monotremes; Therefore, in Australia, marsupials, as a result of divergent development, gave rise to many different forms, externally resembling some placentals. There are marsupial mice, shrews, cats, moles, bears and one species of wolf, as well as a number of forms that have no placental parallels, such as kangaroos, wombats and wallabies.
During the Pleistocene, Australia was home to giant kangaroos and rhino-sized wombats. Opossums are more similar to the primitive ancestral marsupials than any of these more specialized forms; they are the only marsupials found outside of Australia and South America.
Modern highly organized placental mammals, which include humans, characterized by the birth of live young capable of independent existence, descended from insectivorous arboreal ancestors. Fossils of this ancestral form, found in Cretaceous deposits, show that it was a very small animal, like the living shrew. Some of these ancestral mammals retained an arboreal lifestyle and, through a series of intermediate forms, gave rise to primates - monkeys and humans. Others lived on or underground, and during the Paleocene, from them all other mammals living today evolved.
Primitive Paleocene mammals had conical reptilian teeth, five-fingered limbs, and a small brain. In addition, they were plantigrade, not digitigrade.
During the Tertiary period, the evolution of herbaceous plants that served as food and forests that sheltered animals was the most important factor, which influenced changes in the body structure of mammals. Along with the tendency to increase in size, the development of all mammals showed a bias towards an increase in the relative size of the brain and changes in the teeth and legs. When new, more adapted forms appeared, primitive mammals became extinct.
Although fossils of both marsupials and placentals were found in the Cretaceous deposits, the discovery of highly developed mammals in the early Tertiary deposits was quite unexpected. Whether they really arose at this time or existed before in mountainous areas and were simply not preserved in the form of fossils is not known.
In the Paleocene and Eocene, the first predators called creodonts evolved from primitive insectivorous placentals. In the Eocene and Oligocene, they were replaced by more modern forms, which over time gave rise to living predators, such as cats, dogs, bears, weasels, as well as pinnipeds of the sea - seals and walruses.
One of the most famous fossil predators is the saber-toothed tiger, which only recently became extinct during the Pleistocene. It had extremely long and sharp upper fangs, and the lower jaw could swing down and to the side, so that the fangs pierced the victim like sabers.
Large herbivorous mammals, most of which have hooves, are sometimes grouped into one group called ungulates. However, they are not a single natural group, but consist of several independent branches, so that the cow and the horse, despite the presence of hooves in both, are no more related to each other than each of them is to the tiger. The molars of ungulates are flattened and enlarged, which makes it easier to grind leaves and grass. Their legs became long and adapted to the fast running needed to escape predators.
The oldest ungulates, called Condylarthra, appeared in the Paleocene. They had a long body and a long tail, flat grinding molars and short legs ending in five toes with a hoof on each. A group similar to primitive predators, the creodonts, were primitive ungulates called Uintatherians. In the Paleocene and Eocene, some of them reached the size of an elephant, while others had three large horns extending from the top of the head.
The fossil record of several evolutionary lineages of ungulates - horses, camels and elephants - is so complete that it is possible to trace the entire development of these animals from small, primitive five-toed forms. The main direction of evolution in ungulates was towards an increase in overall body size and a decrease in the number of fingers. Ungulates early split into two groups, one of which is characterized by an even number of digits and includes cows, sheep, camels, deer, giraffe, pigs and hippos. Another group is characterized by an odd number of toes and includes horses, zebras, tapirs and rhinoceroses.
The development of elephants and their recently extinct relatives - mammoths and mastodons - can be traced back centuries to an Eocene ancestor that was the size of a pig and had no trunk. This primitive form, called Moeritherium, was close to the trunk, from which also branched such dissimilar forms as the hyrax (a small animal similar to the marmot, found in Africa and Asia) and the sea cow.
Whales and dolphins are descended from Eocene cetacean forms called zeiglodonts, and these latter in turn are believed to have descended from creodonts.
The evolution of bats can be traced back to winged animals that lived in the Eocene and were descendants of primitive insectivores.
The evolution of some other mammals - rodents, rabbits and edentates (anteaters, sloths and armadillos) - is less known.
- Quaternary period (time of man). The Quaternary period, which covers the last 1-1.5 million years, is usually divided into two eras - Pleistocene and modern. The latter began approximately 11,000 years ago, with the retreat of the last glacier. The Pleistocene was characterized by four ice ages, separated by intervals when glaciers retreated. At the time of maximum expansion, ice sheets occupied almost 10 million square meters in North America. km, extending south all the way to the Ohio and Missouri rivers. The Great Lakes, which were plowed by moving glaciers, radically changed their shape many times and from time to time connected with the Mississippi. It has been estimated that in the past, when the Mississippi collected water from lakes as far as Duluth in the west and Buffalo in the east, its flow was more than 60 times greater than it is today. During the Pleistocene glaciations, such an amount of water was removed from the sea and converted into ice that the sea level dropped by 60-90 m. This caused the formation of land connections that served as settlement routes for many terrestrial organisms, between Siberia and Alaska in the Bering Strait region and between England and the European mainland.
Plants and animals of the Pleistocene era were similar to modern ones. It is sometimes difficult to distinguish Pleistocene deposits from Pliocene ones, since the organisms they contain are similar to each other and to modern forms. During the Pleistocene, after the emergence of primitive humans, many mammals became extinct, including the saber-toothed tiger, mammoth, and giant ground sloth. The Pleistocene also saw the extinction of many plant species, especially forest ones, and the appearance of numerous herbaceous forms.
The fossil record leaves no doubt that living species are descended from pre-existing other species. This chronicle is not equally clear for all lines of evolution. The plant tissues are in most cases too soft to yield good fossil remains, and the intermediate forms which serve as links between the different types of animals were apparently skeletal forms of which no trace remains. For many evolutionary lines, in particular for vertebrates, the successive stages of development are well known. There are gaps in other lines that future paleontologists will have to fill.
The oldest sandstones on Earth are those from Western Australia, the age of zircons in which reaches 4.2 billion years. There are publications about an older absolute age of 5.6 billion years or more, but such figures are not accepted by official science. The age of quartzites from Greenland and Northern Canada is determined at 4 billion years, granites of Australia and South Africa up to 3.8 billion years.
The beginning of the Paleozoic is determined at 570 million years, the Mesozoic - at 240 million years, the Cenozoic - at 67 million years
Archean era. The most ancient rocks exposed on the surface of continents were formed in the Archean era. Recognition of these rocks is difficult, since their outcrops are dispersed and in most cases are covered by thick strata of younger rocks. Where these rocks are exposed, they are so metamorphosed that their original character often cannot be restored. During numerous long stages of denudation, thick strata of these rocks were destroyed, and those that survived contain very few fossil organisms and therefore their correlation is difficult or even impossible. It is interesting to note that the oldest known Archean rocks are probably highly metamorphosed sedimentary rocks, and the older rocks overlain by them were melted and destroyed by numerous igneous intrusions. Therefore, traces of the primary earth's crust have not yet been discovered.
There are two large areas of outcrops of Archean rocks in North America. The first of these, the Canadian Shield, is located in central Canada on both sides of Hudson Bay. Although in some places the Archean rocks are overlain by younger ones, in most of the territory of the Canadian Shield they make up the surface. The oldest rocks known in this area are marbles, slate and crystalline schists, interbedded with lavas. Initially, limestone and shales were deposited here, subsequently sealed by lavas. Then these rocks were exposed to powerful tectonic movements, which were accompanied by large granite intrusions. Ultimately, the sedimentary rocks underwent severe metamorphism. After a long period of denudation, these highly metamorphosed rocks were brought to the surface in places, but the general background is granites.
Outcrops of Archean rocks are also found in the Rocky Mountains, where they form the crests of many ridges and individual peaks, such as Pikes Peak. Younger rocks there have been destroyed by denudation.
In Europe, Archean rocks are exposed in the Baltic Shield within Norway, Sweden, Finland and Russia. They are represented by granites and highly metamorphosed sedimentary rocks. Similar outcrops of Archean rocks are found in the south and southeast of Siberia, China, western Australia, Africa and northeast South America. The oldest traces of the vital activity of bacteria and colonies of unicellular blue-green algae Collenia were discovered in Archean rocks of southern Africa (Zimbabwe) and Ontario (Canada).
Proterozoic era. At the beginning of the Proterozoic, after a long period of denudation, the land was largely destroyed, certain parts of the continents were submerged and were flooded by shallow seas, and some low-lying basins began to be filled with continental sediments. In North America, the most significant exposures of Proterozoic rocks are found in four areas. The first of them is confined to the southern part of the Canadian Shield, where thick layers of shales and sandstones of the considered age are exposed around Lake. Upper and northeast of the lake. Huron. These rocks are of both marine and continental origin. Their distribution indicates that the position of shallow seas changed significantly throughout the Proterozoic. In many places, marine and continental sediments are interbedded with thick lava strata. At the end of sedimentation, tectonic movements of the earth's crust occurred, Proterozoic rocks underwent folding and large mountain systems were formed. In the foothills east of the Appalachians there are numerous outcrops of Proterozoic rocks. They were originally deposited as layers of limestone and shale, and then during orogenesis (mountain building) they metamorphosed into marble, slate and crystalline schist. In the Grand Canyon region, a thick sequence of Proterozoic sandstones, shales and limestones unconformably overlie Archean rocks. In the northern Rocky Mountains, a sequence of Proterozoic limestones with a thickness of ca. 4600 m. Although the Proterozoic formations in these areas were affected by tectonic movements and were folded and broken by faults, these movements were not intense enough and could not lead to the metamorphism of rocks. Therefore, the original sedimentary textures were preserved there.
In Europe, there are significant outcrops of Proterozoic rocks within the Baltic Shield. They are represented by highly metamorphosed marbles and slates. In northwestern Scotland, a thick sequence of Proterozoic sandstones overlies Archean granites and crystalline schists. Extensive outcrops of Proterozoic rocks occur in western China, central Australia, southern Africa and central South America. In Australia, these rocks are represented by a thick sequence of unmetamorphosed sandstones and shales, and in eastern Brazil and southern Venezuela - highly metamorphosed slate and crystalline shales.
Fossil blue-green algae Collenia very widespread on all continents in unmetamorphosed limestones of Proterozoic age, where a few fragments of shells of primitive mollusks were also found. However, the remains of animals are very rare, and this indicates that most organisms had a primitive structure and did not yet have hard shells, which are preserved in the fossil state. Although traces of ice ages are recorded for the early stages of Earth's history, extensive glaciation, which had an almost global distribution, is noted only at the very end of the Proterozoic.
Palaeozoic. After the land experienced a long period of denudation at the end of the Proterozoic, some of its territories experienced subsidence and were flooded by shallow seas. As a result of denudation of elevated areas, sedimentary material was carried by water flows into geosynclines, where strata of Paleozoic sedimentary rocks more than 12 km thick accumulated. In North America, at the beginning of the Paleozoic era, two large geosynclines formed. One of them, called the Appalachian, stretches from the North Atlantic Ocean through southeastern Canada and further south to the Gulf of Mexico along the axis of the modern Appalachians. Another geosyncline connected the Arctic Ocean to the Pacific Ocean, passing slightly east of Alaska to the south through eastern British Columbia and western Alberta, then through eastern Nevada, western Utah and southern California. Thus North America was divided into three parts. In certain periods of the Paleozoic, its central regions were partially flooded and both geosynclines were connected by shallow seas. In other periods, as a result of isostatic uplifts of land or fluctuations in the level of the World Ocean, marine regressions occurred, and then terrigenous material washed away from adjacent elevated areas was deposited in geosynclines.
In the Paleozoic, similar conditions existed on other continents. In Europe, huge seas periodically flooded the British Isles, the territories of Norway, Germany, France, Belgium and Spain, as well as a vast area of the East European Plain from the Baltic Sea to the Ural Mountains. Large outcrops of Paleozoic rocks are also found in Siberia, China and northern India. They are indigenous to most areas of eastern Australia, northern Africa, and northern and central South America.
The Paleozoic era is divided into six periods of unequal duration, alternating with short-term stages of isostatic uplifts or marine regressions, during which sedimentation did not occur within the continents (Fig. 9, 10).
Cambrian period - most early period Paleozoic era, named after the Latin name for Wales (Cumbria), where rocks of this age were first studied. In North America, in the Cambrian, both geosynclines were flooded, and in the second half of the Cambrian, the central part of the continent occupied such a low position that both troughs were connected by a shallow sea and layers of sandstones, shales and limestones accumulated there. A major marine transgression was taking place in Europe and Asia. These parts of the world were largely flooded. The exceptions were three large isolated landmasses (the Baltic Shield, the Arabian Peninsula and southern India) and a number of small isolated landmasses in southern Europe and southern Asia. Smaller marine transgressions occurred in Australia and central South America. The Cambrian was characterized by rather calm tectonic conditions.
The deposits of this period preserved the first numerous fossils indicating the development of life on Earth. Although no terrestrial plants or animals were recorded, the shallow epicontinental seas and submerged geosynclines were rich in numerous invertebrate animals and aquatic plants. The most unusual and interesting animals of that time were trilobites (Fig. 11), a class of extinct primitive arthropods, which were widespread in the Cambrian seas. Their calcareous-chitinous shells have been found in rocks of this age on all continents. In addition, there were many types of brachiopods, molluscs, and other invertebrates. Thus, all major forms of invertebrate organisms (with the exception of corals, bryozoans and pelecypods) were present in the Cambrian seas.
At the end of the Cambrian period, most of the land experienced uplift and short-term marine regression occurred.
Ordovician period - the second period of the Paleozoic era (named after the Celtic Ordovician tribe that inhabited the territory of Wales). During this period, the continents again experienced subsidence, as a result of which geosynclines and low-lying basins turned into shallow seas. At the end of the Ordovician ca. 70% of North America was flooded by the sea, in which thick layers of limestone and shales were deposited. The sea also covered large areas of Europe and Asia, partly Australia and the central regions of South America.
All Cambrian invertebrates continued to evolve into the Ordovician. In addition, corals, pelecypods (bivalves), bryozoans and the first vertebrates appeared. In Colorado, in Ordovician sandstones, fragments of the most primitive vertebrates were discovered - jawless (ostracoderms), which lacked real jaws and paired limbs, and the front part of the body was covered with bony plates that formed a protective shell.
Based on paleomagnetic studies of rocks, it has been established that throughout most of the Paleozoic, North America was located in the equatorial zone. Fossil organisms and widespread limestones from this time indicate the dominance of warm, shallow seas in the Ordovician. Australia was located near the South Pole, and northwestern Africa was located in the region of the pole itself, which is confirmed by signs of widespread glaciation imprinted in the Ordovician rocks of Africa.
At the end of the Ordovician period, as a result of tectonic movements, continental uplift and marine regression occurred. In some places, the native Cambrian and Ordovician rocks experienced a process of folding, which was accompanied by the growth of mountains. This ancient stage of orogenesis is called the Caledonian folding.
Silurian. For the first time, rocks of this period were also studied in Wales (the name of the period comes from the Celtic tribe of Silures who inhabited this region).
After the tectonic uplifts that marked the end of the Ordovician period, a denudation stage began, and then at the beginning of the Silurian the continents again experienced subsidence, and the seas flooded the low-lying areas. In North America, in the Early Silurian the area of seas decreased significantly, but in the Middle Silurian they occupied almost 60% of its territory. A thick sequence of marine limestones of the Niagara formation was formed, which received its name from the Niagara Falls, the threshold of which it forms. In the Late Silurian, the areas of the seas were greatly reduced. Thick salt-bearing strata accumulated in a strip stretching from modern Michigan to central New York.
In Europe and Asia, the Silurian seas were widespread and occupied almost the same territories as the Cambrian seas. The same isolated massifs as in the Cambrian, as well as significant areas of northern China and Eastern Siberia, remained unflooded. In Europe, thick limestone strata accumulated along the periphery of the southern tip of the Baltic Shield (currently they are partially submerged by the Baltic Sea). Small seas were common in eastern Australia, northern Africa and central South America.
In general, the same basic representatives of the organic world were found in the Silurian rocks as in the Ordovician. Land plants had not yet appeared in the Silurian. Among invertebrates, corals have become much more abundant, as a result of whose vital activity massive coral reefs have formed in many areas. Trilobites, so characteristic of Cambrian and Ordovician rocks, are losing their dominant significance: they are becoming smaller both in quantity and in species. At the end of the Silurian, many large aquatic arthropods called eurypterids, or crustaceans, appeared.
The Silurian period in North America ended without major tectonic movements. However, in Western Europe at this time the Caledonian belt formed. This mountain range extended across Norway, Scotland and Ireland. Orogenesis also occurred in northern Siberia, as a result of which its territory was raised so high that it was never flooded again.
Devonian named after the county of Devon in England, where rocks of this age were first studied. After the denudation break, certain areas of the continents again experienced subsidence and were flooded by shallow seas. In northern England and partly in Scotland, young Caledonides prevented the penetration of the sea. However, their destruction led to the accumulation of thick strata of terrigenous sandstones in the valleys of foothill rivers. This formation of ancient red sandstones is known for its well-preserved fossil fish. Southern England at this time was covered by a sea in which thick layers of limestone were deposited. Large areas in northern Europe were then flooded by seas in which layers of clayey shales and limestones accumulated. When the Rhine cut into these strata in the area of the Eifel massif, picturesque cliffs were formed that rise along the banks of the valley.
The Devonian seas covered many areas of European Russia, southern Siberia and southern China. A vast sea basin flooded central and western Australia. This area has not been covered by the sea since the Cambrian period. In South America, marine transgression extended to some central and western areas. In addition, there was a narrow sublatitudinal trough in the Amazon. Devonian breeds are very widespread in North America. During most of this period, two major geosynclinal basins existed. In the Middle Devonian, marine transgression spread to the territory of the modern river valley. Mississippi, where a multi-layered strata of limestone has accumulated.
In the Upper Devonian, thick horizons of shale and sandstone formed in the eastern regions of North America. These clastic sequences correspond to a stage of mountain building that began at the end of the Middle Devonian and continued until the end of this period. The mountains extended along the eastern flank of the Appalachian geosyncline (from the modern southeastern United States to southeastern Canada). This region was greatly uplifted, its northern part underwent folding, and then extensive granite intrusions occurred there. These granites are used to make up the White Mountains in New Hampshire, Stone Mountain in Georgia, and a number of other mountain structures. Upper Devonian, so-called The Acadian mountains were reworked by denudation processes. As a result, a layered sequence of sandstones has accumulated to the west of the Appalachian geosyncline, the thickness of which in some places exceeds 1500 m. They are widely represented in the region of the Catskill Mountains, hence the name Catskill sandstones. At the same time, mountain building appeared on a smaller scale in some areas of Western Europe. Orogenesis and tectonic uplift of the earth's surface caused marine regression at the end of the Devonian period.
During the Devonian, some important events occurred in the evolution of life on Earth. The first undisputed discoveries of land plants were made in many areas of the globe. For example, in the vicinity of Gilboa (New York), many species of ferns, including giant trees, were found.
Among the invertebrates, sponges, corals, bryozoans, brachiopods and mollusks were widespread (Fig. 12). There were several types of trilobites, although their numbers and species diversity were significantly reduced compared to the Silurian. The Devonian is often called the “age of fish” due to the magnificent flowering of this class of vertebrates. Although primitive jawless animals still existed, more advanced forms began to predominate. Shark-like fish reached a length of 6 m. At this time, lungfishes appeared, in which the swim bladder was transformed into primitive lungs, which allowed them to exist for some time on land, as well as lobe-finned and ray-finned fish. In the Upper Devonian, the first traces of land animals were discovered - large salamander-like amphibians called stegocephalians. Their skeletal features show that they evolved from lungfishes by further improving their lungs and modifying their fins into limbs.
Carboniferous period. After some break, the continents again experienced subsidence and their low-lying areas turned into shallow seas. Thus began the Carboniferous period, which got its name from the widespread occurrence of coal deposits in both Europe and North America. In America, its early stage, characterized by marine conditions, was previously called Mississippian due to the thick layer of limestone that formed within the modern valley of the river. Mississippian, and is now attributed to the lower Carboniferous period.
In Europe, throughout the Carboniferous period, the territories of England, Belgium and northern France were mostly flooded by the sea, in which thick limestone horizons were formed. Some areas of southern Europe and southern Asia were also flooded, where thick layers of shales and sandstones were deposited. Some of these horizons are continental in origin and contain many fossil remains of terrestrial plants and also host coal-bearing strata. Since Lower Carboniferous formations are poorly represented in Africa, Australia and South America, it can be assumed that these territories were located predominantly in subaerial conditions. In addition, there is evidence of widespread continental glaciation there.
In North America, the Appalachian geosyncline was limited from the north by the Acadian Mountains, and from the south, from the Gulf of Mexico, it was penetrated by the Mississippi Sea, which also flooded the Mississippi Valley. Small sea basins occupied some areas in the west of the continent. In the Mississippi Valley region, a multilayered sequence of limestone and shale accumulated. One of these horizons, the so-called Indian limestone, or spergenite, is a good building material. It was used in the construction of many government buildings in Washington.
At the end of the Carboniferous period, mountain building became widespread in Europe. Chains of mountains stretched from southern Ireland through southern England and northern France into southern Germany. This stage of orogenesis is called Hercynian or Variscian. In North America, local uplifts occurred at the end of the Mississippian period. These tectonic movements were accompanied by marine regression, the development of which was also facilitated by glaciations of the southern continents.
In general, the organic world of the Lower Carboniferous (or Mississippian) time was the same as in the Devonian. However, in addition to a greater variety of types of tree ferns, the flora was replenished with tree mosses and calamites (tree-like arthropods of the horsetail class). Invertebrates were mainly represented by the same forms as in the Devonian. During Mississippian times, sea lilies, bottom-dwelling animals similar in shape to a flower, became more common. Among the fossil vertebrates, shark-like fish and stegocephalians are numerous.
At the beginning of the Late Carboniferous (Pennsylvanian in North America), conditions on the continents began to change rapidly. As follows from the significantly wider distribution of continental sediments, the seas occupied smaller spaces. Northwestern Europe spent most of this time in subaerial conditions. The vast epicontinental Ural Sea extended widely across northern and central Russia, and a major geosyncline extended across southern Europe and southern Asia (the modern Alps, Caucasus, and Himalayas lie along its axis). This trough, called the Tethys geosyncline, or sea, existed over a number of subsequent geological periods.
Lowlands stretched across England, Belgium and Germany. Here, as a result of small oscillatory movements of the earth's crust, an alternation of marine and continental environments occurred. As the sea receded, low-lying swampy landscapes with forests of tree ferns, tree mosses and calamites formed. As the seas advanced, sediments covered the forests, compacting woody remains, which turned into peat and then coal. In Late Carboniferous times, cover glaciation spread across the continents of the Southern Hemisphere. In South America, as a result of marine transgression penetrating from the west, most of the territory of modern Bolivia and Peru was flooded.
In early Pennsylvanian time in North America, the Appalachian geosyncline closed, lost contact with the World Ocean, and terrigenous sandstones accumulated in the eastern and central regions of the United States. During the middle and end of this period, the interior of North America (as well as Western Europe) was dominated by lowlands. Here, shallow seas periodically gave way to swamps that accumulated thick peat deposits that later transformed into large coal basins that stretch from Pennsylvania to eastern Kansas. Parts of western North America were flooded by sea during much of this period. Layers of limestone, shale and sandstone were deposited there.
The widespread occurrence of subaerial environments greatly contributed to the evolution of terrestrial plants and animals. Gigantic forests of tree ferns and club mosses covered the vast swampy lowlands. These forests abounded in insects and arachnids. One of the insect species, the largest in geological history, was similar to the modern dragonfly, but had a wingspan of approx. 75 cm. Stegocephalians reached significantly greater species diversity. Some exceeded 3 m in length. In North America alone, more than 90 species of these giant amphibians, which were similar to salamanders, were discovered in swamp sediments of the Pennsylvanian period. The remains of ancient reptiles were found in these same rocks. However, due to the fragmentary nature of the finds, it is difficult to get a complete picture of the morphology of these animals. These primitive forms were probably similar to alligators.
Permian period. Changes in natural conditions, which began in the Late Carboniferous, became even more pronounced in the Permian period, which ended the Paleozoic era. Its name comes from Perm region in Russia. At the beginning of this period, the sea occupied the Ural geosyncline - a trough that followed the strike of the modern Ural Mountains. A shallow sea periodically covered parts of England, northern France and southern Germany, where layered strata of marine and continental sediments - sandstones, limestones, shales and rock salt - accumulated. The Tethys Sea existed for most of the period, and a thick sequence of limestones formed in the area of northern India and the modern Himalayas. Thick Permian deposits are present in eastern and central Australia and on the islands of South and Southeast Asia. They are widespread in Brazil, Bolivia and Argentina, as well as in southern Africa.
Many Permian formations in northern India, Australia, Africa and South America are of continental origin. They are represented by compacted glacial deposits, as well as widespread fluvio-glacial sands. In Central and Southern Africa, these rocks begin a thick sequence of continental sediments known as the Karoo Series.
In North America, the Permian seas occupied a smaller area compared to previous Paleozoic periods. The main transgression spread from the western Gulf of Mexico north through Mexico and into the south-central United States. The center of this epicontinental sea was located within the modern state of New Mexico, where a thick sequence of Capitanian limestones formed. Thanks to the activity of groundwater, these limestones acquired a honeycomb structure, especially pronounced in the famous Carlsbad Caverns (New Mexico, USA). Farther east, coastal red shale facies were deposited in Kansas and Oklahoma. At the end of the Permian, when the area occupied by the sea was significantly reduced, thick salt-bearing and gypsum-bearing strata formed.
At the end of the Paleozoic era, partly in the Carboniferous and partly in the Permian, orogenesis began in many areas. Thick sedimentary rocks of the Appalachian geosyncline were folded and broken by faults. As a result, the Appalachian Mountains were formed. This stage of mountain building in Europe and Asia is called Hercynian or Variscian, and in North America - Appalachian.
The flora of the Permian period was the same as in the second half of the Carboniferous. However, the plants were smaller and not as numerous. This indicates that the Permian climate became colder and drier. The invertebrate animals of the Permian were inherited from the previous period. A great leap occurred in the evolution of vertebrates (Fig. 13). On all continents, continental sediments of Permian age contain numerous remains of reptiles, reaching a length of 3 m. All of these ancestors of Mesozoic dinosaurs were distinguished by a primitive structure and looked like lizards or alligators, but sometimes had unusual features, for example, a high sail-shaped fin extending from the neck to the tail along the back, in Dimetrodon. Stegocephalians were still numerous.
At the end of the Permian period, mountain building, which manifested itself in many areas of the globe against the background of the general uplift of continents, led to such significant changes in the environment that many characteristic representatives of the Paleozoic fauna began to die out. The Permian period was the final stage of the existence of many invertebrates, especially trilobites.
Mesozoic era, divided into three periods, it differed from the Paleozoic in the predominance of continental settings over marine ones, as well as the composition of flora and fauna. Land plants, many groups of invertebrates, and especially vertebrates have adapted to new environments and undergone significant changes.
Triassic opens the Mesozoic era. Its name comes from the Greek. trias (trinity) in connection with the clear three-membered structure of the sediment strata of this period in northern Germany. Red sandstones lie at the base of the sequence, limestones in the middle, and red sandstones and shales at the top. During the Triassic, large areas of Europe and Asia were occupied by lakes and shallow seas. The epicontinental sea covered Western Europe, and its coastline can be traced throughout England. The above-mentioned stratotype sediments accumulated in this sea basin. The sandstones occurring in the lower and upper parts of the sequence are partly of continental origin. Another Triassic sea basin penetrated into the territory of northern Russia and spread south along the Ural trough. The huge Tethys Sea then covered approximately the same territory as in the Late Carboniferous and Permian times. In this sea, a thick layer of dolomitic limestone has accumulated, which composes the Dolomites of northern Italy. On South central Africa Most of the upper strata of the Karoo continental series are Triassic in age. These horizons are known for the abundance of fossil remains of reptiles. At the end of the Triassic, covers of silts and sands of continental origin formed on the territory of Colombia, Venezuela and Argentina. The reptiles found in these layers show striking similarities to the fauna of the Karoo series of southern Africa.
In North America, Triassic rocks are not as widespread as in Europe and Asia. The products of the destruction of the Appalachians - red continental sands and clays - accumulated in depressions located east of these mountains and experienced subsidence. These deposits, interbedded with lava horizons and sheet intrusions, are faulted and dip to the east. In the Newark Basin in New Jersey and the Connecticut River Valley, they correspond to bedrock of the Newark series. Shallow seas occupied some western areas of North America, where limestones and shales accumulated. Continental sandstones and Triassic shales emerge along the sides of the Grand Canyon (Arizona).
The organic world in the Triassic period was significantly different than in the Permian period. This time is characterized by an abundance of large coniferous trees, the remains of which are often found in Triassic continental deposits. The shales of the Chinle Formation in northern Arizona are loaded with fossilized tree trunks. Weathering of the shale has exposed them and now forms a stone forest. Cycads (or cycadophytes), plants with thin or barrel-shaped trunks and dissected leaves hanging from the top, like those of palm trees, have become widespread. Some cycad species also exist in modern tropical areas. Of the invertebrates, the most common were mollusks, among which ammonites predominated (Fig. 14), which had a vague resemblance to modern nautiluses (or boats) and a multi-chambered shell. There were many species of bivalves. Significant progress has occurred in the evolution of vertebrates. Although stegocephalians were still quite common, reptiles began to predominate, among which many unusual groups appeared (for example, phytosaurs, whose body shape was like that of modern crocodiles, and whose jaws were narrow and long with sharp conical teeth). In the Triassic, true dinosaurs first appeared, evolutionarily more advanced than their primitive ancestors. Their limbs were directed downward, rather than outward (like crocodiles), which allowed them to move like mammals and support their bodies above the ground. Dinosaurs walked on their hind legs, maintaining balance with the help of a long tail (like a kangaroo), and were distinguished by their small stature - from 30 cm to 2.5 m. Some reptiles adapted to life in the marine environment, for example, ichthyosaurs, whose body resembled a shark, and the limbs were transformed into something between flippers and fins, and plesiosaurs, whose torso became flattened, the neck elongated, and the limbs turned into flippers. Both of these groups of animals became more numerous in later stages of the Mesozoic era.
Jurassic period got its name from the Jura Mountains (in northwestern Switzerland), composed of multi-layered strata of limestone, shales and sandstones. One of the largest marine transgressions in Western Europe occurred in the Jurassic. A huge epicontinental sea extended over most of England, France, Germany and penetrated into some western regions of European Russia. In Germany there are numerous outcrops of Upper Jurassic lagoonal fine-grained limestones in which unusual fossils have been discovered. In Bavaria, in the famous town of Solenhofen, remains of winged reptiles and both of the known species of the first birds were found.
The Tethys Sea extended from the Atlantic through the southern part of the Iberian Peninsula along Mediterranean Sea and through South and Southeast Asia it reached the Pacific Ocean. Most of northern Asia during this period was located above sea level, although epicontinental seas penetrated into Siberia from the north. Continental sediments of Jurassic age are known in southern Siberia and northern China.
Small epicontinental seas occupied limited areas along the coast of western Australia. In the interior of Australia there are outcrops of Jurassic continental sediments. Most of Africa during the Jurassic period was located above sea level. The exception was its northern outskirts, which were flooded by the Tethys Sea. In South America, an elongated narrow sea filled a geosyncline located approximately on the site of the modern Andes.
In North America, the Jurassic seas occupied very limited areas in the west of the continent. Thick strata of continental sandstones and capping shales accumulated in the Colorado Plateau region, especially north and east of the Grand Canyon. Sandstones were formed from the sands that made up the desert dune landscapes of the basins. As a result of weathering processes, sandstones have acquired unusual shapes (such as the picturesque pointed peaks in Zion National Park or Rainbow Bridge National Monument, which is an arch rising 94 m above the canyon floor with a span of 85 m; these attractions are located in Utah). The Morrison Shale deposits are famous for the discovery of 69 species of dinosaur fossils. Fine sediments in this area probably accumulated in swampy lowland conditions.
Flora of the Jurassic period general outline was similar to that existing in the Triassic. The flora was dominated by cycad and coniferous tree species. For the first time, ginkgos appeared - gymnosperms, broad-leaved woody plants with leaves that fall in autumn (probably a link between gymnosperms and angiosperms). The only species of this family, Ginkgo biloba, has survived to this day and is considered the most ancient representative of the trees, truly a living fossil.
The Jurassic invertebrate fauna is very similar to the Triassic. However, reef-building corals became more numerous, and sea urchins and mollusks became widespread. Many bivalves related to modern oysters appeared. Ammonites were still numerous.
Vertebrates were represented mainly by reptiles, since stegocephalians became extinct at the end of the Triassic. Dinosaurs have reached the culmination of their development. Herbivorous forms such as Apatosaurus and Diplodocus began to move on four limbs; many had long necks and tails. These animals acquired gigantic sizes (up to 27 m in length), and some weighed up to 40 tons. Some representatives of smaller herbivorous dinosaurs, such as stegosaurs, developed a protective shell consisting of plates and spines. Carnivorous dinosaurs, in particular allosaurs, developed large heads with powerful jaws and sharp teeth; they reached a length of 11 m and moved on two limbs. Other groups of reptiles were also very numerous. Plesiosaurs and ichthyosaurs lived in the Jurassic seas. For the first time, flying reptiles appeared - pterosaurs, which developed membranous wings, like bats, and their mass decreased due to tubular bones.
The appearance of birds in the Jurassic - important stage in the development of the animal world. Two bird skeletons and feather imprints were discovered in the lagoonal limestones of Solenhofen. However, these primitive birds still had many features in common with reptiles, including sharp, conical teeth and long tails.
The Jurassic period ended with intense folding, which resulted in the formation of the Sierra Nevada Mountains in the western United States, which extended further north into modern western Canada. Subsequently, the southern part of this folded belt again experienced uplift, which predetermined the structure of modern mountains. On other continents, manifestations of orogenesis in the Jurassic were insignificant.
Cretaceous period. At this time, thick layered strata of soft, weakly compacted white limestone—chalk—accumulated, from which the period took its name. For the first time, such layers were studied in outcrops along the shores of the Pas-de-Calais Strait near Dover (Great Britain) and Calais (France). In other parts of the world, sediments of this age are also called Cretaceous, although other types of rocks are also found there.
During the Cretaceous period, marine transgressions covered large parts of Europe and Asia. In central Europe, the seas filled two sublatitudinal geosynclinal troughs. One of them was located within southeastern England, northern Germany, Poland and western regions of Russia and in the extreme east reached the submeridional Ural trough. Another geosyncline, Tethys, maintained its previous strike in southern Europe and northern Africa and connected to the southern tip of the Ural trough. Further, the Tethys Sea continued in South Asia and east of the Indian Shield it connected with the Indian Ocean. With the exception of the northern and eastern margins, the territory of Asia was not flooded by the sea throughout the entire Cretaceous period, so continental deposits of this time are widespread there. Thick layers of Cretaceous limestone are present in many areas of Western Europe. In the northern regions of Africa, where the Tethys Sea entered, large strata of sandstones accumulated. The sands of the Sahara Desert were formed mainly due to the products of their destruction. Australia was covered by Cretaceous epicontinental seas. In South America, throughout most of the Cretaceous period, the Andean trough was flooded by the sea. To the east, terrigenous silts and sands with numerous remains of dinosaurs were deposited over a large area of Brazil.
In North America, marginal seas occupied the coastal plains of the Atlantic Ocean and the Gulf of Mexico, where sands, clays and cretaceous limestones accumulated. Another marginal sea was located on the western coast of the mainland within California and reached the southern foot of the revived Sierra Nevada mountains. However, the most recent major marine transgression occurred in western central North America. At this time, a vast geosynclinal trough of the Rocky Mountains formed, and a huge sea spread from the Gulf of Mexico through the modern Great Plains and Rocky Mountains north (west of the Canadian Shield) all the way to the Arctic Ocean. During this transgression, a thick layered sequence of sandstones, limestones and shales was deposited.
At the end of the Cretaceous period, intense orogeny occurred in South and North America and East Asia. In South America, sedimentary rocks accumulated in the Andean geosyncline over several periods were compacted and folded, leading to the formation of the Andes. Similarly, in North America, the Rocky Mountains formed at the site of a geosyncline. Volcanic activity has increased in many areas of the world. Lava flows covered the entire southern part of the Hindustan Peninsula (thus forming the vast Deccan Plateau), and small outpourings of lava took place in Arabia and East Africa. All continents experienced significant uplifts, and regression of all geosynclinal, epicontinental and marginal seas occurred.
The Cretaceous period was marked by several major events in the development of the organic world. The first flowering plants appeared. Their fossil remains are represented by leaves and wood of species, many of which still grow today (for example, willow, oak, maple and elm). The Cretaceous invertebrate fauna is generally similar to the Jurassic. Among vertebrates, the species diversity of reptiles reached a culmination. There were three main groups of dinosaurs. Carnivores with well-developed massive hind limbs were represented by tyrannosaurs, which reached 14 m in length and 5 m in height. A group of bipedal herbivorous dinosaurs (or trachodonts) with wide flattened jaws, reminiscent of a duck's beak, developed. Numerous skeletons of these animals are found in the Cretaceous continental deposits of North America. The third group includes horned dinosaurs with a developed bony shield that protected the head and neck. A typical representative of this group is Triceratops with a short nasal and two long supraorbital horns.
Plesiosaurs and ichthyosaurs lived in the Cretaceous seas, and sea lizards called mosasaurs with an elongated body and relatively small flipper-like limbs appeared. Pterosaurs (flying lizards) lost their teeth and moved better in air space than their Jurassic ancestors. One type of pterosaur, Pteranodon, had a wingspan of up to 8 m.
There are two known species of birds of the Cretaceous period that retained some morphological features of reptiles, for example, conical teeth located in the alveoli. One of them, hesperornis (a diving bird), has adapted to life in the sea.
Although transitional forms more similar to reptiles than to mammals have been known since the Triassic and Jurassic, numerous remains of true mammals were first discovered in continental Upper Cretaceous sediments. The primitive mammals of the Cretaceous period were small in size and somewhat reminiscent of modern shrews.
Widespread mountain building processes on Earth and tectonic uplifts of continents at the end of the Cretaceous period led to such significant changes in nature and climate that many plants and animals became extinct. Among the invertebrates, the ammonites that dominated the Mesozoic seas disappeared, and among the vertebrates, all dinosaurs, ichthyosaurs, plesiosaurs, mosasaurs and pterosaurs disappeared.
Cenozoic era, covering the last 65 million years, is divided into Tertiary (in Russia it is customary to distinguish two periods - Paleogene and Neogene) and Quaternary periods. Although the latter had a short duration (age estimates for its lower limit range from 1 to 2.8 million years), it played great importance in the history of the Earth, since it is associated with repeated continental glaciations and the appearance of man.
Tertiary period. At this time, many areas of Europe, Asia and North Africa were covered by shallow epicontinental and deep geosynclinal seas. At the beginning of this period (in the Neogene), the sea occupied southeastern England, northwestern France and Belgium, and a thick layer of sands and clays accumulated there. The Tethys Sea still existed, stretching from the Atlantic to the Indian Ocean. Its waters flooded the Iberian and Apennine peninsulas, the northern regions of Africa, southwest Asia and the north of Hindustan. Thick limestone horizons were deposited in this basin. Much of northern Egypt is composed of nummulitic limestones, which were used as building material in the construction of the pyramids.
At this time, almost all of southeast Asia was occupied by marine basins and a small epicontinental sea extended to the southeast of Australia. Tertiary marine basins covered the northern and southern ends of South America, and the epicontinental sea penetrated into eastern Colombia, northern Venezuela, and southern Patagonia. Thick strata of continental sands and silts accumulated in the Amazon basin.
The marginal seas were located on the site of the modern Coastal Plains adjacent to the Atlantic Ocean and the Gulf of Mexico, as well as along the western coast of North America. Thick strata of continental sedimentary rocks, formed as a result of denudation of the revived Rocky Mountains, accumulated on the Great Plains and in the intermountain basins.
In many areas of the globe, active orogenesis occurred in the middle of the Tertiary period. The Alps, Carpathians and Caucasus formed in Europe. In North America, during the final stages of the Tertiary period, the Coast Ranges (within the modern states of California and Oregon) and the Cascade Mountains (within Oregon and Washington) were formed.
The Tertiary period was marked by significant progress in the development of the organic world. Modern plants arose back in the Cretaceous period. Most tertiary invertebrates were directly inherited from Cretaceous forms. Modern bony fish have become more numerous, and the number and species diversity of amphibians and reptiles have decreased. There was a leap in the development of mammals. From primitive forms similar to shrews and first appearing in the Cretaceous period, many forms originate, dating back to the beginning of the Tertiary period. The most ancient fossil remains of horses and elephants were found in the Lower Tertiary rocks. Carnivores and even-toed ungulates appeared.
The species diversity of animals increased greatly, but many of them became extinct by the end of the Tertiary period, while others (like some Mesozoic reptiles) returned to a marine lifestyle, such as cetaceans and porpoises, whose fins are transformed limbs. Bats were able to fly thanks to a membrane connecting their long fingers. Dinosaurs, which went extinct at the end of the Mesozoic, gave way to mammals, which became the dominant class of animals on land at the beginning of the Tertiary period.
Quaternary period divided into Eopleistocene, Pleistocene and Holocene. The latter began just 10,000 years ago. The modern relief and landscapes of the Earth were mainly formed in the Quaternary period.
Mountain building, which occurred at the end of the Tertiary period, predetermined a significant rise of continents and regression of the seas. The Quaternary period was marked by a significant cooling of the climate and the widespread development of glaciation in Antarctica, Greenland, Europe and North America. In Europe, the center of glaciation was the Baltic Shield, from where the ice sheet extended to southern England, central Germany and the central regions of Eastern Europe. In Siberia, cover glaciation was smaller, mainly limited to foothill areas. In North America, ice sheets covered a vast area, including most of Canada and the northern regions of the United States down to southern Illinois. In the Southern Hemisphere, the Quaternary ice sheet is characteristic not only of Antarctica, but also of Patagonia. In addition, mountain glaciation was widespread on all continents.
In the Pleistocene, there are four main stages of intensified glaciation, alternating with interglacial periods, during which natural conditions were close to modern or even warmer. The last ice cover in Europe and North America reached its greatest extent 18-20 thousand years ago and finally melted at the beginning of the Holocene.
During the Quaternary period, many tertiary forms of animals became extinct and new ones appeared, adapted to colder conditions. Of particular note are the mammoth and woolly rhinoceros, which inhabited the northern regions in the Pleistocene. In the more southern regions of the Northern Hemisphere, mastodons, saber-toothed tigers, etc. were found. When the ice sheets melted, representatives of the Pleistocene fauna died out and modern animals took their place. Primitive people, in particular Neanderthals, probably existed already during the last interglacial, but modern humans are homo sapiens (Homo sapiens)- appeared only in the last glacial epoch of the Pleistocene, and in the Holocene it spread throughout the globe.
Geological time and methods for its determination
In the study of the Earth as a unique cosmic object, the idea of its evolution occupies a central place, therefore an important quantitative-evolutionary parameter is geological time. This time is studied by a special science called Geochronology– geological chronology. Geochronology May be absolute and relative.
Note 1
Absolute geochronology deals with determining the absolute age of rocks, which is expressed in units of time and, as a rule, in millions of years.
The determination of this age is based on the decay rate of isotopes of radioactive elements. This speed is a constant value and does not depend on the intensity of physical and chemical processes. Age determination is based on nuclear physics methods. Minerals containing radioactive elements, when forming crystal lattices, form a closed system. In this system, the accumulation of radioactive decay products occurs. As a result, the age of a mineral can be determined if the rate of this process is known. The half-life of radium, for example, is $1590$ years, and the complete decay of the element will occur in a time $10$ times longer than the half-life. Nuclear geochronology has its leading methods - lead, potassium-argon, rubidium-strontium and radiocarbon.
Methods of nuclear geochronology made it possible to determine the age of the planet, as well as the duration of eras and periods. Radiological time measurement proposed P. Curie and E. Rutherford at the beginning of the $XX$ century.
Relative geochronology operates with such concepts as “early age, middle age, late age.” There are several developed methods for determining the relative age of rocks. They are combined into two groups - paleontological and non-paleontological.
First play a major role due to their versatility and widespread use. The exception is the absence of organic remains in the rocks. Using paleontological methods, the remains of ancient extinct organisms are studied. Each layer of rocks is characterized by its own complex of organic remains. In each young layer there will be more remains of highly organized plants and animals. The higher the layer lies, the younger it is. A similar pattern was established by the Englishman W. Smith. He owned the first geological map of England, on which rocks were divided by age.
Non-paleontological methods determinations of the relative age of rocks are used in cases where they lack organic remains. More effective then will be stratigraphic, lithological, tectonic, geophysical methods. Using the stratigraphic method, it is possible to determine the sequence of bedding of layers during their normal occurrence, i.e. the underlying strata will be more ancient.
Note 3
The sequence of rock formation determines relative geochronology, and their age in time units is already determined absolute geochronology. Task geological time is to determine the chronological sequence of geological events.
Geochronological table
To determine the age of rocks and study them, scientists use various methods, and for this purpose a special scale has been compiled. Geological time on this scale is divided into time intervals, each of which corresponds to a certain stage in the formation of the earth’s crust and the development of living organisms. The scale was named geochronological table, which includes the following divisions: eon, era, period, epoch, century, time. Each geochronological unit is characterized by its own complex of sediments, which is called stratigraphic: eonothema, group, system, department, tier, zone. A group, for example, is a stratigraphic unit, and the corresponding temporary geochronological unit represents it era. Based on this, there are two scales - stratigraphic and geochronological. The first scale is used when talking about sediments, because at any period of time some geological events occurred on Earth. The second scale is needed to determine relative time. Since its adoption, the content of the scale has changed and been refined.
The largest stratigraphic units at present are eonothems - Archean, Proterozoic, Phanerozoic. On the geochronological scale, they correspond to zones of varying duration. According to the time of existence on Earth, they are distinguished Archean and Proterozoic eonothems, covering almost $80$% of the time. Phanerozoic eon in time is significantly shorter than the previous eons and covers only $570$ million years. This ionoteme is divided into three main groups - Paleozoic, Mesozoic, Cenozoic.
The names of eonothems and groups are of Greek origin:
- Archeos means the most ancient;
- Protheros – primary;
- Paleos – ancient;
- Mesos – average;
- Kainos is new.
From the word " zoiko s", which means vital, the word " zoy" Based on this, eras of life on the planet are distinguished, for example, the Mesozoic era means the era of average life.
Eras and periods
According to the geochronological table, the history of the Earth is divided into five geological eras: Archean, Proterozoic, Paleozoic, Mesozoic, Cenozoic. In turn, eras are divided into periods. There are significantly more of them - $12$. The duration of the periods varies from $20$-$100$ million years. The latter indicates its incompleteness Quaternary period of the Cenozoic era, its duration is only $1.8$ million years.
Archean era. This time began after the formation of the earth's crust on the planet. By this time, there were mountains on Earth and the processes of erosion and sedimentation had come into play. The Archean lasted approximately $2$ billion years. This era is the longest in duration, during which volcanic activity was widespread on Earth, deep uplifts occurred, which resulted in the formation of mountains. Most of the fossils were destroyed under the influence of high temperature, pressure, and mass movement, but little data about that time was preserved. In rocks of the Archean era, pure carbon is found in dispersed form. Scientists believe that these are modified remains of animals and plants. If the amount of graphite reflects the amount of living matter, then there was a lot of it in the Archean.
Proterozoic era. This is the second era in duration, spanning $1$ billion years. Throughout the era, large amounts of sediment were deposited and one significant glaciation occurred. Ice sheets extended from the equator to $20$ degrees of latitude. Fossils found in the rocks of this time are evidence of the existence of life and its evolutionary development. Sponge spicules, remains of jellyfish, fungi, algae, arthropods, etc. were found in Proterozoic sediments.
Palaeozoic. Stands out in this era six periods:
- Cambrian;
- Ordovician,
- Silur;
- Devonian;
- Carbon or coal;
- Perm or Perm.
The duration of the Paleozoic is $370$ million years. During this time, representatives of all types and classes of animals appeared. There were only birds and mammals missing.
Mesozoic era. The era is divided into three period:
- Triassic;
The era began approximately $230$ million years ago and lasted $167$ million years. During the first two periods - Triassic and Jurassic– most of the continental areas rose above sea level. The climate of the Triassic was dry and warm, and in the Jurassic it became even warmer, but was already humid. In state Arizona there is a famous stone forest that has existed since Triassic period. True, all that was left of the once mighty trees were trunks, logs and stumps. At the end of the Mesozoic era, or more precisely in the Cretaceous period, a gradual advance of the sea occurred on the continents. The North American continent sank at the end of the Cretaceous period and, as a result, the waters of the Gulf of Mexico connected with the waters of the Arctic basin. The mainland was divided into two parts. The end of the Cretaceous period is characterized by a large uplift, called Alpine orogeny. At this time, the Rocky Mountains, Alps, Himalayas, and Andes appeared. Intense volcanic activity began in western North America.
Cenozoic era. This new era, which has not yet ended and is currently ongoing.
The era was divided into three periods:
- Paleogene;
- Neogene;
- Quaternary.
Quaternary The period has a number of unique features. This is the time of the final formation of the modern face of the Earth and the ice ages. New Guinea and Australia became independent, moving closer to Asia. Antarctica remained in its place. Two Americas united. Of the three periods of the era, the most interesting is quaternary period or anthropogenic. It continues today, and was isolated in $1829 by a Belgian geologist J. Denoyer. Cold snaps are replaced by warmings, but its most important feature is appearance of man.
Modern man lives in the Quaternary period of the Cenozoic era.
is the totality of all forms of the earth's surface. They can be horizontal, inclined, convex, concave, complex.
The difference in altitude between the highest peak on land, Mount Qomolungma in the Himalayas (8848 m), and the Mariana Trench in the Pacific Ocean (11,022 m) is 19,870 m.
How was the topography of our planet formed? In the history of the Earth, there are two main stages of its formation:
- planetary(5.5-5.0 million years ago), which ended with the formation of the planet, the formation of the Earth’s core and mantle;
- geological, which began 4.5 million years ago and continues to this day. It was at this stage that the formation of the earth's crust occurred.
The source of information about the development of the Earth during the geological stage is primarily sedimentary rocks, which in the vast majority were formed in an aquatic environment and therefore lie in layers. The deeper the layer lies from the earth’s surface, the earlier it was formed and, therefore, is more ancient in relation to any layer that is located closer to the surface and is younger. The concept is based on this simple reasoning relative age of rocks, which formed the basis for the construction geochronological table(Table 1).
The longest time intervals in geochronology are zones(from Greek aion - century, era). The following zones are distinguished: cryptozoic(from Greek cryptos - hidden and zoe- life), covering the entire Precambrian, in the sediments of which there are no remains of skeletal fauna; Phanerozoic(from Greek phaneros - obvious, zoe - life) - from the beginning of the Cambrian to the present time, with rich organic life, including skeletal fauna. The zones are not equivalent in duration; for example, if the Cryptozoic lasted 3-5 billion years, then the Phanerozoic lasted 0.57 billion years.
Table 1. Geochronological table
|
Era. letter designation, duration |
The main stages of life development |
Periods, letter designation, duration |
Major geological events. The appearance of the earth's surface |
Most common minerals |
|
Cenozoic, KZ, about 70 million years |
The dominance of angiosperms. The flourishing of the mammal fauna. The existence of natural zones close to modern ones, with repeated shifts of boundaries |
Quaternary, or anthropogenic, Q, 2 million years |
General rise of the territory. Repeated glaciations. The emergence of man |
Peat. Placer deposits of gold, diamonds, precious stones |
|
Neogene, N, 25 Ma |
The emergence of young mountains in areas of Cenozoic folding. Revival of mountains in areas of all ancient folds. Dominance of angiosperms (flowering plants) |
Brown coals, oil, amber |
||
|
Paleogene, P, 41 Ma |
Destruction of the Mesozoic mountains. Widespread distribution of flowering plants, development of birds and mammals |
Phosphorites, brown coals, bauxites |
||
|
Mesozoic, MZ, 165 Ma |
Melova, K, 70 million years |
The emergence of young mountains in areas of Mesozoic folding. Extinction of giant reptiles. Development of birds and mammals |
Oil, oil shale, chalk, coal, phosphorites |
|
|
Jurassic, J, 50 Ma |
Formation of modern oceans. Hot, humid climate. The heyday of reptiles. Dominance of gymnosperms. The emergence of primitive birds |
Hard coals, oil, phosphorites |
||
|
Triassic, T, 45 Ma |
The greatest retreat of the sea and the rise of continents in the entire history of the Earth. Destruction of pre-Mesozoic mountains. Vast deserts. First mammals |
Rock salts |
||
|
Paleozoic, PZ, 330 Ma |
The blossoming of ferns and other spore-bearing plants. Time of fish and amphibians |
Permian, R, 45 Ma |
The emergence of young mountains in the areas of the Hercynian fold. Dry climate. The emergence of gymnosperms |
Rock and potassium salts, gypsum |
|
Carboniferous (Carboniferous), C, 65 Ma |
Widespread lowland swamps. Hot, humid climate. Development of forests of tree ferns, horsetails and mosses. The first reptiles. The rise of amphibians |
Abundance of coal and oil |
||
|
Devonian, D, 55 million lei |
Reducing the size of the seas. Hot climate. The first deserts. The appearance of amphibians. Numerous fish |
Salts, oil |
||
|
The appearance of animals and plants on Earth |
Silurian, S, 35 Ma |
The emergence of young mountains in the areas of the Caledonian fold. First land plants |
||
|
Ordovician, O, 60 Ma |
Reducing the area of sea basins. The appearance of the first terrestrial invertebrates |
|||
|
Cambrian, E, 70 Ma |
The emergence of young mountains in the areas of the Baikal fold. Flooding of vast areas by seas. The flourishing of marine invertebrates |
Rock salt, gypsum, phosphorites |
||
|
Proterozoic, PR. about 2000 million years |
The origin of life in water. Time for bacteria and algae |
The beginning of the Baikal folding. Powerful volcanism. Time for bacteria and algae |
Huge reserves of iron ores, mica, graphite |
|
|
Archean, AR. more than 1000 million years |
The oldest folds. Intense volcanic activity. Time of primitive bacteria |
Iron ores |
Zones are divided into era. In cryptozoic they distinguish Archean(from Greek archaios- primordial, ancient, aion - century, epoch) and Proterozoic(from Greek proteros - earlier, zoe - life) era; in the Phanerozoic - Paleozoic(from Greek ancient and life), Mesozoic(from Greek tesos - middle, zoe - life) and Cenozoic(from Greek kainos - new, zoe - life).
Eras are divided into shorter periods of time - periods, established only for the Phanerozoic (see Table 1).
Main stages of development of the geographical envelope
The geographical envelope has gone through a long and difficult path of development. In all development, three qualitatively different stages are distinguished: prebiogenic, biogenic, anthropogenic.
Prebiogenic stage(4 billion - 570 million years) - the longest period. At this time, there was a process of increasing the thickness and complication of the composition of the earth's crust. By the end of the Archean (2.6 billion years ago), continental crust with a thickness of about 30 km had already formed over vast areas, and in the early Proterozoic the separation of protoplatforms and protogeosynclines occurred. During this period, the hydrosphere already existed, but the volume of water in it was less than now. Of the oceans (and only towards the end of the Early Proterozoic) one took shape. The water in it was salty and the salinity level was most likely about the same as it is now. But, apparently, in the waters of the ancient ocean the predominance of sodium over potassium was even greater than now; there were also more magnesium ions, which is associated with the composition of the primary earth's crust, the weathering products of which were carried into the ocean.
The Earth's atmosphere at this stage of development contained very little oxygen, and there was no ozone shield.
Life most likely existed from the very beginning of this stage. According to indirect data, microorganisms lived already 3.8-3.9 billion years ago. The discovered remains of simple organisms are 3.5-3.6 billion years old. However, organic life from the moment of its origin until the very end of the Proterozoic did not play a leading, determining role in the development of the geographical envelope. In addition, many scientists deny the presence of organic life on land at this stage.
The evolution of organic life into the prebiogenic stage was slow, but nevertheless, 650-570 million years ago, life in the oceans was quite rich.
Biogenic stage(570 million - 40 thousand years ago) lasted throughout the Paleozoic, Mesozoic and almost the entire Cenozoic, with the exception of the last 40 thousand years.
The evolution of living organisms during the biogenic stage was not smooth: eras of relatively calm evolution were replaced by periods of rapid and profound transformations, during which some forms of flora and fauna became extinct and others became widespread.
Simultaneously with the appearance of terrestrial living organisms, soils as we know them today began to form.
Anthropogenic stage began 40 thousand years ago and continues today. Although man as a biological species appeared 2-3 million years ago, his impact on nature long time remained extremely limited. With the advent of Homo sapiens, this impact increased significantly. This happened 38-40 thousand years ago. This is where the anthropogenic stage in the development of the geographical envelope begins.