Geological periods of the earth. Geological time, eras and periods in the history of the earth

The history of planet Earth already goes back approximately 7 billion years. During this time our common Home has undergone significant changes, which was a consequence of changing periods. V chronological order reveal the entire history of the planet from its very appearance to the present day.

Geological chronology

The history of the Earth, presented in the form of eons, groups, periods and eras, is a certain grouped chronology. At the first international congresses of geology, a special chronological scale was developed, which represented the periodization of the Earth. Subsequently, this scale was replenished with new information and changed, as a result, now it reflects all geological periods in chronological order.

The largest divisions on this scale are eonothems, eras and periods.

Formation of the Earth

The geological periods of the Earth in chronological order begin their history precisely with the formation of the planet. Scientists have concluded that the Earth was formed approximately 4.5 billion years ago. The process of its formation itself was very long and may have begun 7 billion years ago from small cosmic particles. Over time, the gravitational force grew, and along with it, the speed of the bodies falling onto the forming planet increased. Kinetic energy was transformed into heat, resulting in a gradual warming of the Earth.

The Earth's core, according to scientists, was formed over several hundred million years, after which the gradual cooling of the planet began. Currently, the molten core contains 30% of the Earth's mass. The development of other shells of the planet, according to scientists, has not yet been completed.

Precambrian eon

In the geochronology of the Earth, the first eon is called the Precambrian. It covers the time 4.5 billion - 600 million years ago. That is, the lion's share of the planet's history is covered by the former. However, this eon is divided into three more - Katarchean, Archean, Proterozoic. Moreover, often the first of them stands out as an independent eon.

At this time, the formation of land and water occurred. All this happened during active volcanic activity for almost the entire eon. The shields of all continents were formed in the Precambrian, but traces of life are very rare.

Catarchaean Eon

The beginning of the history of the Earth - half a billion years of its existence in science is called catarchaeum. The upper limit of this eon is located at around 4 billion years ago.

Popular literature portrays catarchaea as a time of active volcanic and geothermal changes on the Earth's surface. However, in reality this is not true.

The Catarchaean Eon is a time when volcanic activity did not manifest itself, and the surface of the Earth was a cold, inhospitable desert. Although earthquakes occurred quite often, which smoothed the landscape. The surface looked like dark gray primordial material covered with a layer of regolith. A day at that time was only 6 hours long.

Archean eon

The second main eon of four in the history of the Earth lasted about 1.5 billion years - 4-2.5 billion years ago. At that time, the Earth did not yet have an atmosphere, therefore there was no life yet, however, during this eon, bacteria appeared; due to the lack of oxygen, they were anaerobic. As a result of their activities, today we have deposits of natural resources such as iron, graphite, sulfur and nickel. The history of the term “archaea” dates back to 1872, when it was proposed by the famous American scientist J. Dan. The Archean eon, unlike the previous one, is characterized by high volcanic activity and erosion.

Proterozoic eon

If we consider geological periods in chronological order, the next billion years were occupied by the Proterozoic. This period is also characterized by high volcanic activity and sedimentation, and erosion continues over vast areas.

The formation of the so-called occurs. mountains Currently they are small hills on the plains. The rocks of this eon are very rich in mica, non-ferrous metal ores and iron.

It should be noted that in the Proterozoic period the first living beings appeared - simple microorganisms, algae and fungi. And by the end of the eon, worms, marine invertebrates, and mollusks appear.

Phanerozoic eon

All geological periods in chronological order can be divided into two types - obvious and hidden. Phanerozoic belongs to the obvious ones. At this time, a large number of living organisms with mineral skeletons appear. The era preceding the Phanerozoic was called hidden because practically no traces of it were found due to the lack of mineral skeletons.

The last about 600 million years of the history of our planet are called the Phanerozoic eon. The most significant events of this eon are the Cambrian explosion, which occurred approximately 540 million years ago, and the five largest extinctions in the history of the planet.

Eras of the Precambrian Eon

During the Katarchean and Archean there were no generally recognized eras and periods, so we will skip their consideration.

The Proterozoic consists of three large eras:

Paleoproterozoic- i.e. ancient, including the Siderian, Rhiasian period, Orosirium and Staterium. By the end of this era, oxygen concentrations in the atmosphere had reached modern levels.

Mesoproterozoic- average. Consists of three periods - potassium, ectasia and sthenia. During this era, algae and bacteria reached their greatest prosperity.

Neoproterozoic- new, consisting of Thonium, Cryogenium and Ediacaran. At this time, the formation of the first supercontinent, Rodinia, occurred, but then the plates diverged again. The coldest glacial period took place during an era called the Mesoproterozoic, during which most of the planet froze.

Eras of the Phanerozoic eon

This eon consists of three large eras, sharply different from each other:

Paleozoic, or era ancient life. It began approximately 600 million years ago and ended 230 million years ago. The Paleozoic consists of 7 periods:

1. Cambrian (a temperate climate formed on Earth, the landscape was lowland, during this period the birth of all modern types of animals occurred).
2. Ordovician (the climate throughout the planet is quite warm, even in Antarctica, while the land subsides significantly. The first fish appear).
3. Silurian period (large inland seas are formed, while the lowlands become drier due to the rise of land. The development of fish continues. The Silurian period is marked by the appearance of the first insects).
4. Devonian (appearance of the first amphibians and forests).
5. Lower Carboniferous (dominance of pteridophytes, distribution of sharks).
6. Upper and Middle Carboniferous (appearance of the first reptiles).
7. Perm (most ancient animals die out).

Mesozoic, or the time of reptiles. Geological history consists of three periods:

1. Triassic (seed ferns die out, gymnosperms dominate, the first dinosaurs and mammals appear).
2. Jurassic (part of Europe and western America covered with shallow seas, appearance of the first toothed birds).
3. Chalk (appearance of maple and oak forests, the highest development and extinction of dinosaurs and toothed birds).

Cenozoic, or the time of mammals. Consists of two periods:

1. Tertiary. At the beginning of the period, predators and ungulates reach their dawn, the climate is warm. Forests are expanding to their maximum extent, and ancient mammals are dying out. Approximately 25 million years ago, humans appeared and in the Pliocene era.
2. Quaternary. Pleistocene - large mammals die out, human society emerges, 4 ice ages occur, many plant species become extinct. Modern era - the last ice age ends, the climate gradually takes on its current form. The primacy of man on the entire planet.

The geological history of our planet has a long and contradictory development. In this process, there were several extinctions of living organisms, ice ages were repeated, periods of high volcanic activity were observed, and there were eras of dominance of different organisms: from bacteria to humans. The history of the Earth began approximately 7 billion years ago, it was formed about 4.5 billion years ago, and just less than a million years ago, man ceased to have competitors in all living nature.

The history of our planet still holds many mysteries. Scientists from various fields of natural science have contributed to the study of the development of life on Earth.

Our planet is believed to be about 4.54 billion years old. This entire time period is usually divided into two main stages: Phanerozoic and Precambrian. These stages are called eons or eonothema. Eons, in turn, are divided into several periods, each of which is distinguished by a set of changes that occurred in the geological, biological, and atmospheric state of the planet.

1. Precambrian, or cryptozoic is an eon (time period in the development of the Earth), covering about 3.8 billion years. That is, the Precambrian is the development of the planet from the moment of formation, the formation of the earth’s crust, the proto-ocean and the emergence of life on Earth. By the end of the Precambrian, highly organized organisms with a developed skeleton were already widespread on the planet.

The eon includes two more eonothems - catarchaean and archaean. The latter, in turn, includes 4 eras.

1. Katarhey- this is the time of the formation of the Earth, but there was no core or crust yet. The planet was still a cold cosmic body. Scientists suggest that during this period there was already water on Earth. The Catarchaean lasted about 600 million years.

2. Archaea covers a period of 1.5 billion years. During this period, there was no oxygen on Earth yet, and deposits of sulfur, iron, graphite, and nickel were being formed. The hydrosphere and atmosphere were a single vapor-gas shell that enveloped the globe in a dense cloud. The sun's rays practically did not penetrate through this curtain, so darkness reigned on the planet. 2.1 2.1. Eoarchaean- This is the first geological era, which lasted about 400 million years. The most important event of the Eoarchean was the formation of the hydrosphere. But there was still little water, the reservoirs existed separately from each other and did not yet merge into the world ocean. At the same time Earth's crust becomes solid, although asteroids are still bombarding the Earth. At the end of the Eoarchean, the first supercontinent in the history of the planet, Vaalbara, formed.

2.2 Paleoarchean- the next era, which also lasted approximately 400 million years. During this period, the Earth's core is formed and the magnetic field strength increases. A day on the planet lasted only 15 hours. But the oxygen content in the atmosphere increases due to the activity of emerging bacteria. Remains of these first forms of Paleoarchean life have been found in Western Australia.

2.3 Mesoarchean also lasted about 400 million years. During the Mesoarchean era, our planet was covered by a shallow ocean. The land areas were small volcanic islands. But already during this period the formation of the lithosphere begins and the mechanism of plate tectonics begins. At the end of the Mesoarchean, the first ice age occurs, during which snow and ice first formed on Earth. Biological species are still represented by bacteria and microbial life forms.

2.4 Neoarchaean- the final era of the Archean eon, the duration of which is about 300 million years. Colonies of bacteria at this time form the first stromatolites (limestone deposits) on Earth. The most important event of the Neoarchean was the formation of oxygen photosynthesis.

II. Proterozoic- one of the longest time periods in the history of the Earth, which is usually divided into three eras. During the Proterozoic, the ozone layer appears for the first time, and the world ocean reaches almost its modern volume. And after the long Huronian glaciation, the first multicellular life forms appeared on Earth - mushrooms and sponges. The Proterozoic is usually divided into three eras, each of which contained several periods.

3.1 Paleo-Proterozoic- the first era of the Proterozoic, which began 2.5 billion years ago. At this time, the lithosphere is fully formed. But the previous forms of life practically died out due to an increase in oxygen content. This period was called the oxygen catastrophe. By the end of the era, the first eukaryotes appear on Earth.

3.2 Meso-Proterozoic lasted approximately 600 million years. The most important events of this era: the formation of continental masses, the formation of the supercontinent Rodinia and the evolution of sexual reproduction.

3.3 Neo-Proterozoic. During this era, Rodinia breaks up into about 8 parts, the superocean of Mirovia ceases to exist, and at the end of the era, the Earth is covered with ice almost to the equator. In the Neoproterozoic era, living organisms for the first time begin to acquire a hard shell, which will later serve as the basis of the skeleton.

III. Paleozoic- the first era of the Phanerozoic eon, which began approximately 541 million years ago and lasted about 289 million years. This is the era of the emergence of ancient life. The supercontinent Gondwana unites the southern continents, a little later the rest of the land joins it and Pangea appears. Climatic zones begin to form, and the flora and fauna are represented mainly by marine species. Only towards the end of the Paleozoic did land development begin and the first vertebrates appeared.

The Paleozoic era is conventionally divided into 6 periods.

1. Cambrian period lasted 56 million years. During this period, the main rocks are formed, and a mineral skeleton appears in living organisms. And the most important event of the Cambrian is the emergence of the first arthropods.

2. Ordovician period- the second period of the Paleozoic, which lasted 42 million years. This is the era of the formation of sedimentary rocks, phosphorites and oil shale. The organic world of the Ordovician is represented by marine invertebrates and blue-green algae.

3. Silurian period covers the next 24 million years. At this time, almost 60% of living organisms that existed before die out. But the first cartilaginous and bony fishes in the history of the planet appear. On land, the Silurian is marked by the appearance of vascular plants. Supercontinents are moving closer together and forming Laurasia. By the end of the period, ice melted, sea levels rose, and the climate became milder.

4. Devonian period is characterized by the rapid development of diverse life forms and the development of new ecological niches. The Devonian covers a time period of 60 million years. The first terrestrial vertebrates, spiders, and insects appear. Sushi animals develop lungs. Although, fish still predominate. The flora kingdom of this period is represented by propferns, horsetails, mosses and gosperms.

5. Carboniferous period often called carbon. At this time, Laurasia collides with Gondwana and a new supercontinent Pangea appears. A new ocean is also formed - Tethys. This is the time of the appearance of the first amphibians and reptiles.

6. Permian period- the last period of the Paleozoic, ending 252 million years ago. It is believed that at this time a large asteroid fell on Earth, which led to significant climate change and the extinction of almost 90% of all living organisms. Most of the land is covered with sand, and the most extensive deserts appear that have ever existed in the entire history of the development of the Earth.

IV. Mesozoic- the second era of the Phanerozoic eon, which lasted almost 186 million years. At this time, the continents acquired almost modern outlines. A warm climate contributes to the rapid development of life on Earth. Giant ferns disappear and are replaced by angiosperms. The Mesozoic is the era of dinosaurs and the appearance of the first mammals.

The Mesozoic era is divided into three periods: Triassic, Jurassic and Cretaceous.

1. Triassic period lasted just over 50 million years. At this time, Pangea begins to break apart, and the internal seas gradually become smaller and dry out. The climate is mild, the zones are not clearly defined. Almost half of the land's plants are disappearing as deserts spread. And in the kingdom of fauna the first warm-blooded and land reptiles appeared, which became the ancestors of dinosaurs and birds.

2. Jurassic covers a span of 56 million years. The Earth had a humid and warm climate. The land is covered with thickets of ferns, pines, palms, and cypresses. Dinosaurs reign on the planet, and numerous mammals were still distinguished by their small stature and thick hair.

3. Cretaceous period- the longest period of the Mesozoic, lasting almost 79 million years. The separation of the continents is almost ending, the Atlantic Ocean is significantly increasing in volume, and ice sheets are forming at the poles. An increase in the water mass of the oceans leads to the formation of a greenhouse effect. At the end of the Cretaceous period, a catastrophe occurs, the causes of which are still not clear. As a result, all dinosaurs and most species of reptiles and gymnosperms became extinct.

V. Cenozoic- this is the era of animals and homo sapiens, which began 66 million years ago. At this time, the continents acquired their modern shape, Antarctica occupied the south pole of the Earth, and the oceans continued to expand. Plants and animals that survived the disaster of the Cretaceous period found themselves in a completely new world. Unique communities of life forms began to form on each continent.

The Cenozoic era is divided into three periods: Paleogene, Neogene and Quaternary.

1. Paleogene period ended approximately 23 million years ago. At this time, a tropical climate reigned on Earth, Europe was hidden under evergreen tropical forests, only in the north of the continents did deciduous trees grow. It was during the Paleogene period that mammals developed rapidly.

2. Neogene period covers the next 20 million years of the planet's development. Whales and bats appear. And, although saber-toothed tigers and mastodons still roam the earth, the fauna is increasingly acquiring modern features.

3. Quaternary period began more than 2.5 million years ago and continues to this day. Two major events characterize this time period: the Ice Age and the emergence of man. The Ice Age completely completed the formation of the climate, flora and fauna of the continents. And the appearance of man marked the beginning of civilization.

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 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 large quantity precipitation 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 ahead by 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 animals existed only for certain periods of time, their fossil remains allow geologists to compare sediments of the same age found in different places.

• Cambrian period [show] .

  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). Sea bottom 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] .

  During the Cambrian period, the continents began to gradually submerge, 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] .

  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] .

  

  

  

  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] .

  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] .

  

  

  Last period 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:

1. Triassic
2. Jurassic
3. 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 inner part 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. Significant difference What separates snakes from 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 gave rise to 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 with equal right 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 whole line forms that have no parallels among placentals, 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 marmot-like animal 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 moment of maximum expansion, the ice sheets occupied North America almost 10 million sq. 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. Plant tissues are in most cases too soft to yield good fossil remains, and intermediate forms that serve as links between different types animals were obviously forms without a skeleton, and no traces of them remained. 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.

Hello! In this article I want to tell you about the geochronological column. This is a column of periods of the Earth's development. And also in more detail about each era, thanks to which you can paint a picture of the formation of the Earth throughout its history. What types of life appeared first, how they changed, and how much it took.

The geological history of the Earth is divided into large intervals - eras, eras are divided into periods, periods are divided into epochs. This division was associated with events that took place on. Changes in the abiotic environment influenced the evolution of the organic world on Earth.

Geological eras of the Earth, or geochronological scale:

And now about everything in more detail:

Designations:
Eras;
Periods;
Epochs.

1. Catarchaean era (from the creation of the Earth, about 5 billion years ago, to the origin of life);

2. Archean era , the most ancient era (3.5 billion - 1.9 billion years ago);

3. Proterozoic era (1.9 billion – 570 million years ago);

The Archean and Proterozoic are still combined into the Precambrian. The Precambrian covers the largest portion of geological time. Areas of land and sea were formed, and active volcanic activity occurred. Shields of all continents were formed from Precambrian rocks. Traces of life are usually rare.

4. Palaeozoic (570 million - 225 million years ago) with such periods :

Cambrian period(from the Latin name for Wales)(570 million – 480 million years ago);

The transition to the Cambrian was marked by the unexpected appearance huge amount fossils. This is a sign of the beginning of the Paleozoic era. Marine flora and fauna flourished in numerous shallow seas. Trilobites were especially widespread.

Ordovician period(from the British Ordovician tribe)(480 million – 420 million years ago);

Much of the Earth was soft, and most of the surface was still covered by seas. The accumulation of sedimentary rocks continued, and mountain building occurred. There were reef-formers. An abundance of corals, sponges and mollusks was noted.

Silurian (from the British Silure tribe)(420 million - 400 million years ago);

Dramatic events in the history of the Earth began with the development of jawless fish-like fish (the first vertebrates), which appeared in the Ordovician. Another significant event was the appearance of the first land animals in the Late Silurian.

Devonian (from Devonshire in England)(400 million – 320 million years ago);

In the Early Devonian, mountain-building movements reached their peak, but basically it was a period of spasmodic development. The first seed plants settled on land. A large variety and number of fish-like species were noted, and the first terrestrial animals developed. animals- amphibians.

Carboniferous or Carboniferous period (from the abundance of coal in the seams) (320 million – 270 million years ago);

Mountain building, folding, and erosion continued. In North America, swampy forests and river deltas were flooded, and large coal deposits were formed. Southern continents were covered by glaciation. Insects spread rapidly, and the first reptiles appeared.

Permian period (from the Russian city of Perm)(270 million – 225 million years ago);

On a large part of Pangea - the supercontinent that united everything - conditions prevailed. Reptiles spread widely and modern insects evolved. New terrestrial flora developed, including conifers. Several marine species have disappeared.

5. Mesozoic era (225 million - 70 million years ago) with such periods:

Triassic (from the tripartite division of the period proposed in Germany)(225 million – 185 million years ago);

With the onset of the Mesozoic era, Pangea began to disintegrate. On land, the dominance of conifers was established. Diversity among reptiles was noted, with the first dinosaurs and giant marine reptiles appearing. Primitive mammals evolved.

Jurassic period(from mountains in Europe)(185 million – 140 million years ago);

Significant volcanic activity was associated with the formation of the Atlantic Ocean. Dinosaurs dominated on land, flying reptiles and primitive birds conquered the air ocean. There are traces of the first flowering plants.

Cretaceous period (from the word "chalk")(140 million – 70 million years ago);

During the maximum expansion of the seas, chalk was deposited, especially in Britain. The dominance of dinosaurs continued until the extinction of them and other species at the end of the period.

6. Cenozoic era (70 million years ago - up to our time) with such periods And epochs:

Paleogene period (70 million – 25 million years ago);

— Paleocene epoch ("oldest part of the new epoch")(70 million – 54 million years ago);
— Eocene Epoch ("dawn of a new era")(54 million – 38 million years ago);
— Oligocene Epoch ("not very new")(38 million – 25 million years ago);

Neogene period (25 million – 1 million years ago);

— Miocene Epoch ("relatively new")(25 million – 8 million years ago);
— Pliocene Epoch ("very recent")(8 million – 1 million years ago);

The Paleocene and Neogene periods are still combined into the Tertiary period. With the onset of the Cenozoic era (new life), mammals began to spread spasmodically. Many large species evolved, although many became extinct. The number of flowering plants has increased sharply plants. As the climate cooled, herbaceous plants appeared. There was a significant uplift of the land.

Quaternary period (1 million – our time);

— Pleistocene epoch (“most recent”)(1 million – 20 thousand years ago);

— Holocene era(“a completely new era”) (20 thousand years ago – our time).

This is the last geological period, including the present tense. Four major glaciations alternated with warming periods. The number of mammals has increased; they have adapted to . The formation of man - the future ruler of the Earth - took place.

There are also other ways of dividing eras, epochs, periods, eons are added to them, and some epochs are still divided, like on this table, for example.

But this table is more complex, the confusing dating of some eras is purely chronological, not based on stratigraphy. Stratigraphy is the science of determining the relative geological age of sedimentary rocks, the division of rock strata, and the correlation of different geological formations.

This division, of course, is relative, since there was no sharp distinction from today to tomorrow in these divisions.

But still, at the turn of neighboring eras and periods, significant geological transformations predominantly took place: processes of mountain formation, redistribution of seas, changing of the climate etc.

Each subsection was, of course, characterized by its unique flora and fauna.

, And You can read it in the same section.

Thus, these are the main eras of the Earth on which all scientists rely 🙂

The emergence of the Earth and the early stages of its formation

One of the important tasks modern natural science in the field of geosciences is the restoration of the history of its development. According to modern cosmogonic concepts, the Earth was formed from gas and dust matter scattered in the protosolar system. One of the most likely options for the emergence of the Earth is as follows. First, the Sun and a flattened rotating circumsolar nebula were formed from an interstellar gas and dust cloud under the influence, for example, of the explosion of a nearby supernova. Next, the evolution of the Sun and the circumsolar nebula occurred with the transfer of angular momentum from the Sun to the planets by electromagnetic or turbulent-convective methods. Subsequently, the “dusty plasma” condensed into rings around the Sun, and the material of the rings formed the so-called planetesimals, which condensed into planets. After this, a similar process was repeated around the planets, leading to the formation of satellites. It is believed that this process took about 100 million years.

It is assumed that further, as a result of differentiation of the Earth's substance under the influence of its gravitational field and radioactive heating, shells of the Earth, different in chemical composition, state of aggregation and physical properties, emerged and developed - the Earth's geosphere. The heavier material formed a core, probably composed of iron mixed with nickel and sulfur. Some lighter elements remained in the mantle. According to one hypothesis, the mantle is composed of simple oxides of aluminum, iron, titanium, silicon, etc. The composition of the earth's crust has already been discussed in some detail in § 8.2. It is composed of lighter silicates. Even lighter gases and moisture formed the primary atmosphere.

As already mentioned, it is assumed that the Earth was born from a cluster of cold solid particles that fell out of a gas-dust nebula and stuck together under the influence of mutual attraction. As the planet grew, it heated up due to the collision of these particles, which reached several hundred kilometers, like modern asteroids, and the release of heat not only by the naturally radioactive elements now known to us in the crust, but also by more than 10 radioactive isotopes AI, Be, that have become extinct since then. Cl, etc. As a result, complete (in the core) or partial (in the mantle) melting of the substance could occur. In the initial period of its existence, up to approximately 3.8 billion years, the Earth and other terrestrial planets, as well as the Moon, were subjected to intense bombardment by small and large meteorites. The consequence of this bombardment and the earlier collision of planetesimals could be the release of volatiles and the beginning of the formation of a secondary atmosphere, since the primary one, consisting of gases captured during the formation of the Earth, most likely quickly dissipated in outer space. Somewhat later, the hydrosphere began to form. The atmosphere and hydrosphere thus formed were replenished during the process of degassing of the mantle during volcanic activity.

The fall of large meteorites created extensive and deep craters, similar to those currently observed on the Moon, Mars, and Mercury, where their traces have not been erased by subsequent changes. Cratering could provoke outpourings of magma with the formation of basalt fields similar to those covering the lunar “seas”. This is probably how the primary crust of the Earth was formed, which, however, was not preserved on its modern surface, with the exception of relatively small fragments in the “younger” continental-type crust.

This crust, which already contains granites and gneisses, although with a lower content of silica and potassium than in “normal” granites, appeared at the turn of about 3.8 billion years and is known to us from outcrops within the crystalline shields of almost all continents. The method of formation of the oldest continental crust is still largely unclear. In the composition of this crust, which is everywhere metamorphosed under conditions of high temperatures and pressures, rocks are found whose textural features indicate accumulation in an aquatic environment, i.e. in this distant era the hydrosphere already existed. The emergence of the first crust, similar to the modern one, required the supply of large quantities of silica, aluminum, and alkalis from the mantle, while now mantle magmatism creates a very limited volume of rocks enriched in these elements. It is believed that 3.5 billion years ago, gray gneiss crust, named after the predominant type of rocks composing it, was widespread across the area of ​​modern continents. In our country, for example, it is known on the Kola Peninsula and in Siberia, in particular in the river basin. Aldan.

Principles of periodization of the geological history of the Earth

Subsequent events in geological time are often determined according to relative geochronology, categories “ancient”, “younger”. For example, some era is older than some other. Individual segments of geological history are called (in order of decreasing duration) zones, eras, periods, epochs, centuries. Their identification is based on the fact that geological events are imprinted in rocks, and sedimentary and volcanogenic rocks are located in layers in the earth's crust. In 1669, N. Stenoi established the law of bedding sequence, according to which the underlying layers of sedimentary rocks are older than the overlying ones, i.e. formed before them. Thanks to this, it became possible to determine the relative sequence of formation of layers, and therefore the geological events associated with them.

The main one in relative geochronology is the biostratigraphic, or paleontological, method of establishing the relative age and sequence of occurrence of rocks. This method was proposed by W. Smith at the beginning of the 19th century, and then developed by J. Cuvier and A. Brongniard. The fact is that in most sedimentary rocks you can find the remains of animal or plant organisms. J.B. Lamarck and Charles Darwin established that animal and plant organisms over the course of geological history gradually improved in the struggle for existence, adapting to changing living conditions. Some animal and plant organisms died out at certain stages of the Earth's development, and were replaced by others, more advanced ones. Thus, from the remains of previously living, more primitive ancestors found in some layer, one can judge the relatively more ancient age of this layer.

Another method of geochronological division of rocks, especially important for the division of igneous formations of the ocean floor, is based on the property of magnetic susceptibility of rocks and minerals formed in the Earth's magnetic field. With a change in the orientation of the rock relative to the magnetic field or the field itself, part of the “innate” magnetization is retained, and the change in polarity is reflected in a change in the orientation of the remanent magnetization of the rocks. Currently, a scale of change of such eras has been established.

Absolute geochronology - the study of the measurement of geological time expressed in ordinary absolute astronomical units(years) - determines the time of occurrence, completion and duration of all geological events, primarily the time of formation or transformation (metamorphism) of rocks and minerals, since the age of geological events is determined by their age. The main method here is to analyze the ratio of radioactive substances and their decay products in rocks formed in different eras.

The oldest rocks are currently established in Western Greenland (3.8 billion years old). The longest age (4.1 - 4.2 billion years) was obtained from zircons from Western Australia, but the zircon here occurs in a redeposited state in Mesozoic sandstones. Taking into account the ideas about the simultaneous formation of all planets of the Solar system and the Moon and the age of the most ancient meteorites (4.5-4.6 billion years) and ancient lunar rocks (4.0-4.5 billion years), the age of the Earth is taken to be 4.6 billion years

In 1881, at the II International Geological Congress in Bologna (Italy), the main divisions of combined stratigraphic (for separating layered sedimentary rocks) and geochronological scales were approved. According to this scale, the history of the Earth was divided into four eras in accordance with the stages of development of the organic world: 1) Archean, or Archeozoic - the era of ancient life; 2) Paleozoic - the era of ancient life; 3) Mesozoic - era average life; 4) Cenozoic - era of new life. In 1887, the Proterozoic era was distinguished from the Archean era - the era of primary life. Later the scale was improved. One of the options for the modern geochronological scale is presented in Table. 8.1. The Archean era is divided into two parts: early (older than 3500 million years) and late Archean; Proterozoic - also into two: early and late Proterozoic; in the latter, the Riphean (the name comes from the ancient name of the Ural Mountains) and Vendian periods are distinguished. The Phanerozoic zone is divided into Paleozoic, Mesozoic and Cenozoic eras and consists of 12 periods.

Table 8.1. Geochronological scale

The main stages of the evolution of the earth's crust

Let us briefly consider the main stages of the evolution of the earth's crust as an inert substrate on which the diversity of the surrounding nature developed.

INapxee The still quite thin and plastic crust, under the influence of stretching, experienced numerous discontinuities through which basaltic magma again rushed to the surface, filling troughs hundreds of kilometers long and many tens of kilometers wide, known as greenstone belts (they owe this name to the predominant greenschist low-temperature metamorphism of basaltic rocks). breeds). Along with basalts, among the lavas of the lower, most powerful part of the section of these belts, there are high-magnesium lavas, indicating a very high degree of partial melting of mantle matter, which indicates a high heat flow, much higher than today. The development of greenstone belts consisted of a change in the type of volcanism in the direction of an increase in the content of silicon dioxide (SiO 2), in compression deformations and metamorphism of sedimentary-volcanogenic fulfillment, and, finally, in the accumulation of clastic sediments, indicating the formation of mountainous terrain.

After the change of several generations of greenstone belts, the Archean stage of the evolution of the earth's crust ended 3.0 -2.5 billion years ago with the massive formation of normal granites with a predominance of K 2 O over Na 2 O. Granitization, as well as regional metamorphism, which in some places reached the highest level, led to the formation of mature continental crust over most of the area of ​​modern continents. However, this crust also turned out to be insufficiently stable: at the beginning of the Proterozoic era it experienced fragmentation. At this time, a planetary network of faults and cracks arose, filled with dikes (plate-shaped geological bodies). One of them, the Great Dyke in Zimbabwe, is more than 500 km long and up to 10 km wide. In addition, rifting appeared for the first time, giving rise to zones of subsidence, powerful sedimentation and volcanism. Their evolution led to the creation at the end early Proterozoic(2.0-1.7 billion years ago) folded systems that re-fused fragments of the Archean continental crust, which was facilitated by a new era of powerful granite formation.

As a result, by the end of the Early Proterozoic (at the turn of 1.7 billion years ago), mature continental crust already existed on 60-80% of the area of ​​its modern distribution. Moreover, some scientists believe that at this turn the entire continental crust formed a single mass - the supercontinent Megagaea (big earth), which on the other side of the globe was opposed by an ocean - the predecessor of the modern Pacific Ocean - Megathalassa (big sea). This ocean was less deep than modern oceans, because the growth of the volume of the hydrosphere due to degassing of the mantle in the process of volcanic activity continues throughout the subsequent history of the Earth, although more slowly. It is possible that the prototype of Megathalassa appeared even earlier, at the end of the Archean.

In the Catarchean and early Archean, the first traces of life appeared - bacteria and algae, and in the late Archean, algal calcareous structures - stromatolites - spread. In the Late Archean, a radical change in the composition of the atmosphere began, and in the Early Proterozoic ended: under the influence of plant activity, free oxygen appeared in it, while the Catarchean and Early Archean atmosphere consisted of water vapor, CO 2, CO, CH 4, N, NH 3 and H 2 S with an admixture of HC1, HF and inert gases.

In the Late Proterozoic(1.7-0.6 billion years ago) Megagaia began to gradually split, and this process sharply intensified at the end of the Proterozoic. Its traces are extended continental rift systems buried at the base of the sedimentary cover of ancient platforms. Its most important result was the formation of vast intercontinental mobile belts - the North Atlantic, Mediterranean, Ural-Okhotsk, which separated the continents of North America, Eastern Europe, East Asia and the largest fragment of Megagaea - the southern supercontinent Gondwana. The central parts of these belts developed on the newly formed ocean crust during rifting, i.e. the belts represented ocean basins. Their depth gradually increased as the hydrosphere grew. At the same time, mobile belts developed along the periphery of the Pacific Ocean, the depth of which also increased. Climatic conditions became more contrasting, as evidenced by the appearance, especially at the end of the Proterozoic, of glacial deposits (tillites, ancient moraines and fluvio-glacial sediments).

Paleozoic stage The evolution of the earth's crust was characterized by the intensive development of mobile belts - intercontinental and continental margins (the latter on the periphery of the Pacific Ocean). These belts were divided into marginal seas and island arcs, their sedimentary-volcanogenic strata experienced complex fold-thrust and then normal fault deformations, granites were intruded into them and folded mountain systems were formed on this basis. This process was uneven. It distinguishes a number of intense tectonic epochs and granitic magmatism: Baikal - at the very end of the Proterozoic, Salair (from the Salair ridge in Central Siberia) - at the end of the Cambrian, Takovsky (from the Takovsky Mountains in the eastern USA) - at the end of the Ordovician, Caledonian ( from the ancient Roman name for Scotland) - at the end of the Silurian, Acadian (Acadia is the ancient name of the northeastern states of the USA) - in the middle of the Devonian, Sudeten - at the end of the Early Carboniferous, Saale (from the Saale River in Germany) - in the middle of the Early Permian. The first three tectonic eras of the Paleozoic are often combined into the Caledonian era of tectogenesis, the last three - into the Hercynian or Variscan. In each of the listed tectonic epochs, certain parts of the mobile belts turned into folded mountain structures, and after destruction (denudation) they became part of the foundation of young platforms. But some of them partially experienced activation in subsequent eras of mountain building.

By the end of the Paleozoic, the intercontinental mobile belts were completely closed and filled with folded systems. As a result of the withering away of the North Atlantic belt, the North American continent closed with the East European continent, and the latter (after the completion of the development of the Ural-Okhotsk belt) with the Siberian continent, and the Siberian continent with the Chinese-Korean one. As a result, the supercontinent Laurasia was formed, and the death of the western part of the Mediterranean belt led to its unification with the southern supercontinent - Gondwana - into one continental block - Pangea. At the end of the Paleozoic - beginning of the Mesozoic, the eastern part of the Mediterranean belt turned into a huge bay of the Pacific Ocean, along the periphery of which folded mountain structures also rose.

Against the background of these changes in the structure and topography of the Earth, the development of life continued. The first animals appeared in the late Proterozoic, and at the very dawn of the Phanerozoic, almost all types of invertebrates existed, but they were still devoid of shells or shells, which have been known since the Cambrian. In the Silurian (or already in the Ordovician), vegetation began to emerge on land, and at the end of the Devonian, forests existed, which became most widespread in the Carboniferous period. Fish appeared in the Silurian, amphibians - in the Carboniferous.

Mesozoic and Cenozoic eras - the last major stage in the development of the structure of the earth's crust, which is marked by the formation of modern oceans and the separation of modern continents. At the beginning of the stage, in the Triassic, Pangea still existed, but already in the early Jurassic period it again split into Laurasia and Gondwana due to the emergence of the latitudinal Tethys Ocean, stretching from Central America to Indochina and Indonesia, and in the west and east it connected with the Pacific Ocean (Fig. 8.6); this ocean included the Central Atlantic. From here, at the end of the Jurassic, the process of continental spreading spread to the north, creating during the Cretaceous and early Paleogene the North Atlantic, and starting from the Paleogene - the Eurasian basin of the Arctic Ocean (the Amerasian basin arose earlier as part of the Pacific Ocean). As a result, North America separated from Eurasia. In the Late Jurassic, the formation of the Indian Ocean began, and from the beginning of the Cretaceous, the South Atlantic began to open from the south. This marked the beginning of the collapse of Gondwana, which existed as a single entity throughout the Paleozoic. At the end of the Cretaceous, the North Atlantic joined the South Atlantic, separating Africa from South America. At the same time, Australia separated from Antarctica, and at the end of the Paleogene the latter separated from South America.

Thus, by the end of the Paleogene, all modern oceans took shape, all modern continents became isolated, and the appearance of the Earth acquired a form that was basically close to the present one. However, there were no modern mountain systems yet.

Intense mountain building began in the late Paleogene (40 million years ago), culminating in the last 5 million years. This stage of the formation of young fold-cover mountain structures and the formation of revived arched block mountains is identified as neotectonic. In fact, the neotectonic stage is a substage of the Mesozoic-Cenozoic stage of the Earth's development, since it was at this stage that the main features of the modern relief of the Earth took shape, starting with the distribution of oceans and continents.

At this stage, the formation of the main features of modern fauna and flora was completed. The Mesozoic era was the era of reptiles, mammals became dominant in the Cenozoic, and humans appeared in the late Pliocene. At the end of the Early Cretaceous, angiosperms appeared and the land acquired grass cover. At the end of the Neogene and Anthropocene, the high latitudes of both hemispheres were covered by powerful continental glaciation, relics of which are the ice caps of Antarctica and Greenland. This was the third major glaciation in the Phanerozoic: the first took place in the Late Ordovician, the second at the end of the Carboniferous - beginning of the Permian; both of them were distributed within Gondwana.

QUESTIONS FOR SELF-CONTROL

What are spheroid, ellipsoid and geoid? What are the parameters of the ellipsoid adopted in our country? Why is it needed?

What is the internal structure of the Earth? On what basis is a conclusion made about its structure?

What are the main physical parameters Earths and how do they change with depth?

What is the chemical and mineralogical composition of the Earth? On what basis is a conclusion made about the chemical composition of the entire Earth and the earth's crust?

What are the main types of the earth's crust currently distinguished?

What is the hydrosphere? What is the water cycle in nature? What are the main processes occurring in the hydrosphere and its elements?

What is atmosphere? What is its structure? What processes occur within its boundaries? What is weather and climate?

Define endogenous processes. What endogenous processes do you know? Briefly describe them.

What is the essence of plate tectonics? What are its main provisions?

10. Define exogenous processes. What is the main essence of these processes? What endogenous processes do you know? Briefly describe them.

11. How do endogenous and exogenous processes interact? What are the results of the interaction of these processes? What is the essence of the theories of V. Davis and V. Penk?

What are the modern ideas about the origin of the Earth? How did its early formation as a planet occur?

What is the basis for periodization of the geological history of the Earth?

14. How did the earth's crust develop in the geological past of the Earth? What are the main stages in the development of the earth's crust?

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