What eras were there on earth? Geological periods in chronological order

Life on Earth began over 3.5 billion years ago, immediately after the completion of the formation of the earth's crust. Throughout time, the emergence and development of living organisms influenced the formation of relief and climate. Also, tectonic and climatic changes that occurred over many years influenced the development of life on Earth.

A table of the development of life on Earth can be compiled based on the chronology of events. The entire history of the Earth can be divided into certain stages. The largest of them are eras of life. They are divided into eras, eras into epochs, epochs into centuries.

Eras of life on Earth

The entire period of the existence of life on Earth can be divided into 2 periods: the Precambrian, or cryptozoic (primary period, 3.6 to 0.6 billion years), and the Phanerozoic.

The Cryptozoic includes the Archean (ancient life) and Proterozoic (primary life) eras.

The Phanerozoic includes the Paleozoic (ancient life), Mesozoic (middle life) and Cenozoic (new life) eras.

These 2 periods of life development are usually divided into smaller ones - eras. The boundaries between eras are global evolutionary events, extinctions. In turn, eras are divided into periods, and periods into epochs. The history of the development of life on Earth is directly related to changes in the earth’s crust and the planet’s climate.

Eras of development, countdown

The most significant events are usually identified in special time intervals - eras. Time is counted down in reverse order, from ancient life to modern life. There are 5 eras:

1. Archean.
2. Proterozoic.
3. Paleozoic.
4. Mesozoic.
5. Cenozoic.

Periods of development of life on Earth

The Paleozoic, Mesozoic and Cenozoic eras include periods of development. These are smaller periods of time compared to eras.

Palaeozoic:

• Cambrian (Cambrian).
• Ordovician.
• Silurian (Silurian).
• Devonian (Devonian).
• Carboniferous (carbon).
• Perm (Perm).

Mesozoic era:

• Triassic (Triassic).
• Jurassic (Jurassic).
• Cretaceous (chalk).

Cenozoic era:

• Lower Tertiary (Paleogene).
• Upper Tertiary (Neogene).
• Quaternary, or Anthropocene (human development).

The first 2 periods are included in the Tertiary period lasting 59 million years.

Table of the development of life on Earth

Era, period	Duration	Live nature	Inanimate nature, climate
Archean era (ancient life)	3.5 billion years	The appearance of blue-green algae, photosynthesis. Heterotrophs	The predominance of land over the ocean, the minimum amount of oxygen in the atmosphere.
Proterozoic era (early life)	2.7 billion years	The appearance of worms, mollusks, the first chordates, soil formation.	The land is a rocky desert. Accumulation of oxygen in the atmosphere.
The Paleozoic era includes 6 periods:
1. Cambrian (Cambrian)	535-490 Ma	Development of living organisms.	Hot climate. The land is deserted.
2. Ordovician	490-443 Ma	The appearance of vertebrates.	Almost all platforms are flooded with water.
3. Silurian (Silurian)	443-418 Ma	Exit of plants to land. Development of corals, trilobites.	with the formation of mountains. The seas dominate the land. The climate is varied.
4. Devonian (Devonian)	418-360 Ma	The appearance of mushrooms and lobe-finned fish.	Formation of intermountain depressions. Prevalence of dry climate.
5. Coal (carbon)	360-295 Ma	The appearance of the first amphibians.	Subsidence of continents with flooding of territories and the emergence of swamps. There is a lot of oxygen and carbon dioxide in the atmosphere.
6. Perm (Perm)	295-251 Ma	Extinction of trilobites and most amphibians. The beginning of the development of reptiles and insects.	Volcanic activity. Hot climate.
The Mesozoic era includes 3 periods:
1. Triassic (Triassic)	251-200 million years	Development of gymnosperms. The first mammals and bony fish.	Volcanic activity. Warm and sharply continental climate.
2. Jurassic (Jurassic)	200-145 million years	The emergence of angiosperms. Distribution of reptiles, appearance of the first bird.	Mild and warm climate.
3. Cretaceous (chalk)	145-60 million years	The appearance of birds and higher mammals.	Warm climate followed by cooling.
The Cenozoic era includes 3 periods:
1. Lower Tertiary (Paleogene)	65-23 million years	The rise of angiosperms. The development of insects, the emergence of lemurs and primates.	Mild climate with distinct climatic zones.
2. Upper Tertiary (Neogene)	23-1.8 million years	The appearance of ancient people.	Dry climate.
3. Quaternary or Anthropocene (human development)	1.8-0 Ma	The appearance of man.	Cold weather.

Development of living organisms

The table of the development of life on Earth involves division not only into time periods, but also into certain stages of the formation of living organisms, possible climate changes (ice age, global warming).

• Archean era. The most significant changes in the evolution of living organisms are the appearance of blue-green algae - prokaryotes capable of reproduction and photosynthesis, and the emergence of multicellular organisms. The appearance of living protein substances (heterotrophs) capable of absorbing organic substances dissolved in water. Subsequently, the appearance of these living organisms made it possible to divide the world into plant and animal.

• Mesozoic era.

• Triassic. Distribution of plants (gymnosperms). Increase in the number of reptiles. The first mammals, bony fish.
• Jurassic period. The predominance of gymnosperms, the emergence of angiosperms. The appearance of the first bird, the flourishing of cephalopods.
• Cretaceous period. Distribution of angiosperms, decline of other plant species. Development of bony fishes, mammals and birds.

• Cenozoic era.
  • Lower Tertiary period (Paleogene). The rise of angiosperms. Development of insects and mammals, appearance of lemurs, later primates.
  • Upper Tertiary period (Neogene). The formation of modern plants. The appearance of human ancestors.
  • Quaternary period (Anthropocene). Formation of modern plants and animals. The appearance of man.

Development of inanimate conditions, climate change

The table of the development of life on Earth cannot be presented without data on changes in inanimate nature. The emergence and development of life on Earth, new species of plants and animals, all this is accompanied by changes in inanimate nature and climate.

Climate Change: Archean Era

The history of the development of life on Earth began through the stage of the predominance of land over water resources. The relief was poorly outlined. The atmosphere is dominated by carbon dioxide, the amount of oxygen is minimal. Shallow waters have low salinity.

The Archean era is characterized by volcanic eruptions, lightning, and black clouds. The rocks are rich in graphite.

Climatic changes in the Proterozoic era

The land is a rocky desert; all living organisms live in water. Oxygen accumulates in the atmosphere.

Climate Change: Paleozoic Era

During various periods of the Paleozoic era the following occurred:

• Cambrian period. The land is still deserted. The climate is hot.
• Ordovician period. The most significant changes are the flooding of almost all northern platforms.
• Silurian. Tectonic changes and conditions of inanimate nature are varied. Mountain formation occurs and the seas dominate the land. Areas of different climates, including areas of cooling, have been identified.
• Devonian. The climate is dry and continental. Formation of intermountain depressions.
• Carboniferous period. Subsidence of continents, wetlands. The climate is warm and humid, with a lot of oxygen and carbon dioxide in the atmosphere.
• Permian period. Hot climate, volcanic activity, mountain building, drying out of swamps.

During the Paleozoic era, mountains were formed. Such changes in relief affected the world's oceans - sea basins were reduced, and a significant land area was formed.

The Paleozoic era marked the beginning of almost all major oil and coal deposits.

Climatic changes in the Mesozoic

The climate of different periods of the Mesozoic is characterized by the following features:

• Triassic. Volcanic activity, climate is sharply continental, warm.
• Jurassic period. Mild and warm climate. The seas dominate the land.
• Cretaceous period. Retreat of the seas from the land. The climate is warm, but at the end of the period global warming gives way to cooling.

In the Mesozoic era, previously formed mountain systems are destroyed, the plains go under water (Western Siberia). In the second half of the era, the Cordillera, the mountains of Eastern Siberia, Indochina, and partly Tibet were formed, and the mountains of Mesozoic folding were formed. The prevailing climate is hot and humid, promoting the formation of swamps and peat bogs.

Climate Change - Cenozoic Era

During the Cenozoic era, a general rise of the Earth's surface occurred. The climate has changed. Numerous glaciations of the earth's surfaces advancing from the north changed the appearance of the continents of the Northern Hemisphere. Thanks to such changes, the hilly plains were formed.

• Lower Tertiary period. Mild climate. Division into 3 climatic zones. Formation of continents.
• Upper Tertiary period. Dry climate. The emergence of steppes and savannas.
• Quaternary period. Multiple glaciations of the northern hemisphere. Cooling climate.

All changes during the development of life on Earth can be written down in the form of a table that will reflect the most significant stages in the formation and development of the modern world. Despite the already known research methods, even now scientists continue to study history, making new discoveries that allow modern society to learn how life developed on Earth before the advent of man.

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 Archeozoic a lifeless era: in the Archeozoic 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 millipedes.

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 burrowed into 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) well conveys their 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 their general appearance it is difficult to confuse them with other fossils, but at the same time it is necessary to warn young geologists about how difficult it can be to identify individual types 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 also existed 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 lungfish, 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. In appearance, stegocephals were somewhat reminiscent of salamanders and often reached significant 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 widespread, 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 restore 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.

Slender, hollow inside trunks of 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 poor resistance to fracture.

Strong winds and especially storms broke trees, felled huge forests, and to replace them 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 - “carrying 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)

The thesis about the evolution of the Earth, as an exceptional cosmic object of its kind, occupies the main stage. In view of this, geological time becomes a special numerical-evolutionary characteristic. The science that deals with the comprehension of this time is Geochronology, that is, the geological account of time. The above specialized science is divided into two types: absolute geochronology and relative geochronology.

Absolute geochronology carries out the activity of determining the absolute age of rocks. This age is expressed in units of time, namely, in millions of years.

The key element in establishing this age is the decay rate of isotopes of radioactive components. This speed is extremely constant and free from the saturation of physical and chemical currents. The designation of age is organized in ways that are related to nuclear physics. Minerals that contain radioactive components give rise to a closed structure when arranging crystal lattices. It is in such a structure that the process of accumulation of radioactive decay elements occurs. Therefore, if you have information about the speed of the presented process, you can find out how old the mineral is. For example, the half-life of radium is about 1590 years. And the final decay of this element will occur over a period of time that is ten times longer than the half-life. Nuclear geochronology has the main methods, namely: lead, potassium-argon, rubidium-strontium and radiocarbon.

It was the presented methods of nuclear geochronology that contributed to establishing the age of the planet and the time of eras and periods. At the beginning of the 20th century, P. Curie and E. Rutherford introduced a different technique for setting the time, which was called radiological. Relative geochronology carries out the activity of determining the relative age of rocks. That is, which accumulations in the earth’s crust are younger and which are ancient.

The specialization of relative geochronology consists of such theses as “early, middle and late age”. A number of methods for identifying the relative age of rocks have a scientific basis. These methods can be divided into two groups. These groups are called paleontological and non-paleontological. Paleontological methods occupy a leading position, since they are more multifunctional and are applied on a wide front. Of course, there are exceptions. Such a rare case is the absence of natural accumulations in rocks. They use the presented method when studying fragments of extinct ancient organisms. It is worth noting that each rock layer is characterized by a specific set of natural remains. The Englishman W. Smith discovered a certain chronology in the age characteristics of breeds. Namely, the higher the layer is, the younger it is in age. Consequently, the content of microorganism residues in it will be an order of magnitude higher. Also, W. Smith owns the first geological map of England. On this map, the scientist divided the rocks by age.

Non-paleontological methods for determining the relative age of rocks are used in cases where there are no organic remains in the rocks being studied. In this case, there are stratigraphic, lithological, tectonic and geophysical methods. For example, when using the stratigraphic method, it is possible to establish the chronology of the formation of layers at their standard occurrence, namely, those layers that lie below will be more ancient.

The establishment of the chronology of rock formation is carried out by relative geochronology, while absolute geochronology is involved in specifically determining the age in units of time. The purpose of geological time is to discover the temporal chronology of geological phenomena.

Geochronological table

In order to establish age criteria for rocks, scientists use a wide variety of methods. Therefore, it was appropriate to create a highly specialized scale for ease of use. Geological time according to this scale is divided into time intervals. A certain segment is characterized by a specific stage in the structure of the earth’s crust and the formation of living organisms. The presented scale is called a geochronological table. It has such subgroups as eon, era, period, epoch, century, time. It is worth noting that each group is characterized by a certain set of savings. Such a set, in turn, is called a stratigraphic complex, which also has a number of types, namely: eonothem, group, system, department, stage, zone. For example, a system belongs to the stratigraphic category, and the time group of the geochronological department belongs to its characteristic subgroup, which is called an era. As a consequence, there are two scales: stratigraphic and geochronological. The stratigraphic school is used in cases where accumulations in rocks are studied. Since at any time there are some geological processes taking place on the planet. The geochronological scale is used to establish relative time. Since the time the scale was approved, its structure has undergone many changes.

Today, the most voluminous stratigraphic category is eonothems. It is divided into Archean, Proterozoic and Phanerozoic. On the geochronological scale, these classes are subject to categories of diverse activities. Based on the time of existence on Earth, scientists have identified two eonothems: Archean and Proterozoic. It was these eonothems that contained about eighty percent of the total time. The remaining Phanerozoic eonothem is significantly smaller than the previous eons, since it covered only about five hundred and seventy million years. This eonothem is divided into three main classes: Paleozoic, Mesozoic and Cenozoic.

The names of eonotemes and classes come from the Greek language:

• Archeos - the most ancient;
• Protheros - primary;
• Paleos – ancient;
• Mesos – average;
• Kainos – new;

From the word form “zoikos”, which has the definition of “vital”, the word “zoy” was formed. Based on this word formation, scientists have identified eras of life on Earth. For example, the Paleozoic era means the era of ancient life.

Eras and periods

Based on the geochronological table, experts divided the history of the planet into five geological eras. The above eras received the following names: Archean, Proterozoic, Paleozoic, Mesozoic, Cenozoic. Also, these eras are divided into periods. The number of these time periods is twelve, which apparently exceeds the number of eras. The duration of these stages is from twenty to one hundred million years. The last period of the Cenozoic era is not completed, since its time span is about two million years.

Archean era. This era began to exist after the formation and structuring of the earth’s crust on the planet. By this time period, there were already rocks on the planet and the processes of erosion and accumulation of sediments began. This era lasted about two billion years. Scientists consider the Archean era to be the longest in time. During its course, volcanic processes were active on the planet, the depths were uplifted, which contributed to the formation of mountains. Unfortunately, most of the fossils were destroyed, but some general information about this era still remains. In rocks that existed in the Archean era, scientists discovered carbon in its pure form. Experts believe that these are modified remains of living organisms. Since the amount of graphite indicates the amount of living matter, there was quite a lot of it in this era.

Proterozoic era. In terms of time, this is the next period, which contains one billion years. During this era, precipitation accumulated and one global glaciation occurred. The fossils that were found in the mountain layers of this time are the main witnesses that life existed and went through stages of evolution. The remains of jellyfish, mushrooms, algae and much more were discovered in the rock layers.

Palaeozoic. This era is divided into six time periods:

• Cambrian;
• Ordovician;
• Silur;
• Devonian;
• Carbon/Coal;
• Perm/Perm;

The time period of the Paleozoic era covers three hundred and seventy million years. During this period, representatives of all classes of the animal world appeared. Only birds and mammals were missing.

Mesozoic era. Experts have identified three stages:

• Triassic;

This period covers a time period of one hundred and sixty-seven million years. During the first two periods, the main part of the continents rose above sea level. Climatic conditions gradually changed and became warmer. Arizona has a popular rock forest that has existed since the Triassic period. During the last period, a gradual rise of the sea occurs. The North American continent was completely submerged in water, as a result of which the Gulf of Mexico connected with the Arctic basin. The end of the Cretaceous period is characterized by the fact that large uplifts of the earth's crust occurred. This is how the Rocky Mountains, the Alps, the Himalayas, and the Andes appeared.

Cenozoic era. This period continues to this day. Experts divide it into three periods:

• Paleogene;
• Neogene;
• Quaternary;

The last period is characterized by special features. During this period, the final formation of the planet took place. New Guinea and Australia became isolated. Two Americas merged. This time period was identified by J. Denoyer in 1829. The main feature is that a man appeared.

It is during this period that all of humanity lives today.

I have long been interested in the history of our planet. After all, the world we see today was not always like this. It is difficult to even imagine what was on our planet many millions or even several billion years ago. Each period was characterized by some of its own characteristics.

What were the main eras and periods on our planet?

I’ll touch a little on the topic of eras and periods in general terms. So, scientists divide all 4.5 billion years like this.

• The Precambrian Era (Catarchaean, Archean and Proterozoic periods) - in terms of duration, this is the longest era, which lasted almost 4 billion years.
• The Paleozoic era (includes six periods) lasted a little less than 290 million years, at which time the conditions for life were finally formed, first in water and then on land.
• The Mesozoic era (includes three periods) is the era of reptile dominance on our planet.
• The Cenozoic era (consists of the Paleogene, Neogene and Anthropocene periods) - we now live in this era, and to be more specific, in the Anthropocene.

Each era usually ended with some kind of cataclysm.

Mesozoic era

Almost everyone knows about this era, because many have seen the American film “Jurassic Park,” in which different breeds of dinosaurs appear. Yes, yes, these were the animals that dominated at that time.

The Mesozoic consists of the following segments:

• Triassic;
• Jurassic;
• chalky.

During the Jurassic period, dinosaurs reached their greatest development. There were giant species that reached a length of up to thirty meters. There were also very large and tall trees, and there was minimal vegetation on the ground. Ferns predominated among low-growing plants.

At the beginning of this era there was a single continent, but then it split into six parts, which over time took on its modern appearance.

Two million years before the extinction of the dinosaurs, the most formidable predator appeared - the Tyrannosaurus. And these reptiles became extinct after the earth collided with a comet. As a result, approximately 65% ​​of all life on the planet died.

This era ended approximately sixty-five million years ago.

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

One of the important tasks of modern natural science in the field of Earth sciences is to restore 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 the 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 - the era of middle 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

			Age (beginning),
Phanerozoic	Cenozoic	Quaternary
		Neogene
		Paleogene
	Mesozoic
		Triassic
	Paleozoic	Permian
		Coal
		Devonian
		Silurian
		Ordovician
		Cambrian
cryptozoic	Proterozoic	Vendian
		Riphean
		Karelian
	Archean
	Catarhean

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 again welded together 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 constituted a single massif - 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 of the Earth 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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