Geological periods in chronological order. Geological history of the Earth. Geological time, eras and periods in the history of planet earth

Bones of dinosaurs and amazing extinct animals have been found in different eras human history. In the absence of science, legends about giants or dragons were formed from the bones found. Only modern people with the development of science were able to study the main stages of the development of life on Earth using paleontological finds.

Earth Education

Our planet was formed about 4.5 billion years ago from star dust and solid particles. As gravity increased, the Earth began to attract debris and rocks from space, which fell to the surface, gradually warming the planet. Over time, the top layer became denser and began to cool. The hot mantle maintains heat until now, preventing the Earth from turning into a block of ice.

For a long time the planet was in a lifeless state. The atmosphere was filled with various gases and did not contain oxygen. Due to the release of large amounts of steam from the bowels of the Earth and gravity, dense clouds began to form. Intense rains contributed to the emergence of the World Ocean, in which life originated.

Rice. 1. Formation of the Earth.

Oxygen appeared in the atmosphere with the appearance of the first photosynthetic plants.

Stages of development

Life on Earth is associated with geological eons and eras. An eon is a large segment of geological history that unites several eras. In turn, eras are divided into periods. Each era is characterized by individual development of the animal and plant world, which often depended on climate, condition earth's crust, underground activities.

Rice. 2. Eras of the geological history of the Earth.

A more detailed description of the eons is presented in the table of the main stages of the development of life on Earth.

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Eon	Era	Period	Characteristic
Katarhey			It began about 4.5 billion years ago and ended 4 billion years ago. Sedimentary rocks are unknown. The surface of the planet is lifeless and dotted with craters
			Lasted from 4 to 2.5 billion years ago. At the end of the Eoarchean, the first unicellular organisms appeared - anaerobic bacteria. Formation of carbonate deposits and minerals. Formation of continents. Oxygen is formed in the Neoarchaean thanks to cyanobacteria
	Paleoarchaean
	Mesoarchean
	Neoarchaean
Proterozoic	Paleoproterozoic		The period is from 2.5 to 1.6 billion years ago. More advanced cyanobacteria release large amounts of oxygen, which leads to an oxygen catastrophe. Oxygen becomes destructive for anaerobic organisms. The first aerobic eukaryotes arise in stateria
		Orosirium
		Staterius
	Mesoproterozoic		Lasted 1.6-1 billion years ago. Sedimentary rocks are formed. In ectasia, the first multicellular organisms appear - red algae. In sthenia, eukaryotes arise that reproduce sexually
	Neoproterozoic		It began 1 billion years ago and ended 542 million years ago. Severe glaciation of the earth's crust. The first multicellular soft-bodied animals—vendobionts—appear in the Ediacaran region.
		Cryogenium
		Ediacaran
Phanerozoic	Paleozoic		Lasted from 541 to 290 million years ago. At the beginning of the era, species diversity of living organisms appears. An extinction event occurred between the Ordovician and Silurian, as a result of which more than 60% of living beings disappeared, but already in the Devonian, life began to develop new ecological niches. Horsetails, ferns, gymnosperms, a large number of lobe-finned fish, the first vertebrate land animals, insects, spiders, and ammonites appeared. At the end of the Devonian, extinction also occurs. In the Carboniferous, reptiles, amphibians, mollusks, bryozoans, arthropods, and cartilaginous fish appear. During the Permian period, beetles, lacewing insects, and predatory animals appeared
			It began 252 million years ago and ended 66 million years ago. At the junction of the Permian and Triassic, the largest mass extinction occurs, as a result of which 90% of marine inhabitants and 70% of terrestrial ones disappear. In the Jurassic period, the first flowering plants appeared, displacing gymnosperms. Reptiles and insects occupy a dominant position. During the Cretaceous period there was a cooling and the extinction of most plants. This leads to the death of herbivores and then predatory reptiles. The first birds and mammals take their place
	Cenozoic	Paleogene	It began 66 million years ago and continues to this day. Variety of birds, plants, insects. Whales, sea urchins, cephalopods, elephants, and horses appear. In the Anthropocene - the current period - about 2 million years ago the first people (Homo) arose

According to modern ideas, has an age of 4.5 - 5 billion years. In the history of its occurrence, planetary and geological stages are distinguished.

Geological stage- sequence of events in the development of the Earth as planets since the formation of the earth's crust. During it, relief forms arose and were destroyed, the land submerged under water (the advance of the sea), the retreat of the sea, glaciations, the appearance and disappearance of various types animals and plants, etc.

Scientists, trying to reconstruct the history of the planet, study rock layers. They divide all deposits into 5 groups, distinguishing the following eras: Archean (ancient), Proterozoic (early), Paleozoic (ancient), Mesozoic (middle) and Cenozoic (new). The border between eras passes through the largest evolutionary events. The last three eras are divided into periods because in these deposits the remains of animals and plant remains were better preserved and in greater quantity.

Each era is characterized by events that had a decisive influence on modern life. relief.

Archean era was distinguished by violent volcanic activity, as a result of which igneous granite-containing rocks appeared on the surface of the Earth - the basis of future continents. At that time, the Earth was inhabited only by microorganisms that could live without oxygen. It is believed that the sediments of that era cover individual areas of land with an almost continuous shield; they contain a lot of iron, gold, silver, platinum and ores of other metals.

IN Proterozoic era Volcanic activity was also high, and mountains of the so-called Baikal fold were formed. They have practically not been preserved and now represent only isolated small uplifts on the plains. During this period, the planet was inhabited by blue-green algae and protozoan microorganisms, and the first multicellular organisms arose. Proterozoic rock layers are rich in minerals: iron ores and ores of non-ferrous metals, mica.

At first Paleozoic era formed mountains Caledonian folding, which led to the reduction of sea basins and the emergence of large areas of land. Only isolated ridges of the Urals, Arabia, Southeast China and Central Europe have been preserved in the form of mountains. All these mountains are low, “worn out”. In the second half of the Paleozoic, the mountains of the Hercynian fold were formed. This era of mountain building was more powerful; vast mountain ranges arose in Western Siberia and the Urals, Mongolia and Manchuria, most of Central Europe, the eastern coast of North America and Australia. Now they are represented by low blocky mountains. In the Paleozoic era, the Earth was inhabited by fish, amphibians and reptiles, and algae predominated among the vegetation. The main deposits of oil and coal arose during this period.

Mesozoic era began with a period of relative calm of the internal forces of the Earth, the gradual destruction of previously created mountain systems and the immersion of flattened plain areas, for example, most of Western Siberia, under water. In the second half of the era, mountains of Mesozoic folding were formed. At this time, vast mountainous countries appeared, which even now have the appearance of mountains. These are the Cordillera, the mountains of Eastern Siberia, certain parts of Tibet and Indochina. The ground was covered with lush vegetation, which gradually died and rotted. In the hot and humid climate, swamps and peat bogs were actively formed. This was the age of the dinosaurs. Giant predatory and herbivorous animals have spread throughout almost the entire planet. The first mammals appeared at this time.

Cenozoic era continues to this day. Its beginning was marked by an increase in the activity of the Earth's internal forces, which led to a general rise of the surface. During the era of Alpine folding, young folded mountains arose within the Alpine-Himalayan belt and the continent of Eurasia acquired its modern shape. In addition, there was a rejuvenation of the ancient mountain ranges of the Urals, Appalachians, Tien Shan, and Altai. The climate on the planet changed sharply, and a period of powerful ice sheets began. Ice sheets advancing from the north changed the topography of the continents of the Northern Hemisphere, forming hilly plains with big amount lakes

The entire geological history of the Earth can be traced on a geochronological scale - a table of geological time, showing the sequence and subordination of the main stages of geology, the history of the Earth and the development of life on it (see Table 4 on pp. 46-49). The geochronological table should be read from bottom to top.

Questions and tasks to prepare for the exam

1. Explain why polar days and nights are observed on Earth.
2. What would conditions be like on Earth if its axis of rotation were not inclined to the orbital plane?
3. The change of seasons on Earth is determined by two main reasons: the first is the rotation of the Earth around the Sun; name the second one.
4. How many times a year and when is the Sun at its zenith above the equator? Over the Northern Tropic? Over the South Tropic?
5. In what direction do constant winds and sea currents moving in the meridional direction deviate in the Northern Hemisphere?
6. When is the shortest night in the Northern Hemisphere?
7. What are the characteristics of the days of spring and autumn equinox on the ground? When do they occur in the Northern and Southern Hemispheres?
8. When are the summer and winter solstices in the Northern and Southern Hemispheres?
9. In what light zones is the territory of our country located?
10. List the geological periods of the Cenozoic era, starting with the most ancient.

Table 4

Geochronological scale

Eras (duration - in million years)	Periods (duration in million years)	The most important events in the history of the Earth	Characteristic minerals formed at this time
1	2	3	4
Cenozoic 70 million years	Quaternary 2 Ma (Q)	General rise of land. Repeated glaciations, especially in the Northern Hemisphere. The emergence of man	Peat, placer deposits of gold, diamonds, precious stones
	Neogene 25 Ma (N)	The emergence of young mountains in areas of Alpine folding. Rejuvenation of mountains in areas of all ancient folds. Dominance of flowering plants	Brown coals, oil, amber
	Paleogene 41 Ma (P)	Destruction of the mountains of Mesozoic folding. Widespread development of flowering plants, birds and mammals	Phosphorites, brown coals, bauxites

Mesozoic 165 million years	Cretaceous 70 Ma (K)	The emergence of young mountains in areas of Mesozoic folding. Extinction of giant reptiles (dinosaurs). Development of birds and mammals	Oil, oil shale, chalk, coal, phosphorites
	Jurassic 50 Ma (J)	Formation of modern oceans. Hot and humid climate over most of the land. The rise of giant reptiles (dinosaurs). Dominance of gymnosperms	Hard coals, oil, phosphorites
	Triassic 40 Ma (T)	The greatest retreat of the sea and rise of land in the entire history of the Earth. Destruction of the mountains of the Caledonian and Hercynian folds. Vast deserts. First mammals	Rock salts
1	2	3	4
Paleozoic 330 million years	Permian 45 Ma (P)	The emergence of young folded mountains in the areas of the Hercynian fold. Dry climate over most of the land. The emergence of gymnosperms	Rock and potassium salts, gypsum
	Carboniferous 65 Ma (C)	Hot and humid climate over most of the land. Widespread marshy lowlands in coastal areas. Forests of tree ferns. The first reptiles, the rise of amphibians	Coal, oil
	Devonian 55 Ma (r)	Hot climate over most of the land. The first deserts. The appearance of amphibians. Numerous fish	Salts, oil
	Silurian 35 Ma (S)	The emergence of young folded mountains in the areas of the Caledonian folding. First land plants(moss mosses and ferns)

	Ordovician 60 Ma (O)	Reducing the area of ​​sea basins. Appearance of the first terrestrial invertebrates
	Cambrian 70 Ma	The emergence of young mountains in the areas of the Baikal fold. Flooding of vast areas by seas. The flourishing of marine invertebrates	Rock salt, gypsum, phosphorites
Proterozoic era 600 million years		The beginning of the Baikal folding. Powerful volcanism. Development of bacteria and blue-green algae	Iron ores, mica, graphite
Archean era 900 million years		Formation of the continental crust. Intense volcanic activity. The time of primitive single-celled bacteria	Ore

Maksakovsky V.P., Petrova N.N., Physical and economic geography of the world. - M.: Iris-press, 2010. - 368 pp.: ill.

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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 outline. 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 the dominance of reptiles 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 oldest sandstones on Earth are those from Western Australia, the age of zircons in which reaches 4.2 billion years. There are publications about an older absolute age of 5.6 billion years or more, but such figures are not accepted by official science. The age of quartzites from Greenland and Northern Canada is determined at 4 billion years, granites of Australia and South Africa up to 3.8 billion years.

The beginning of the Paleozoic is determined at 570 million years, the Mesozoic - at 240 million years, the Cenozoic - at 67 million years

Archean era. The most ancient rocks exposed on the surface of continents were formed in the Archean era. Recognition of these rocks is difficult because their outcrops are dispersed and in most cases are covered by thick strata of younger rocks. Where these rocks are exposed, they are so metamorphosed that their original character often cannot be restored. During numerous long stages of denudation, thick strata of these rocks were destroyed, and those that survived contain very few fossil organisms and therefore their correlation is difficult or even impossible. It is interesting to note that the oldest known Archean rocks are probably highly metamorphosed sedimentary rocks, and the older rocks overlain by them were melted and destroyed by numerous igneous intrusions. Therefore, traces of the primary earth's crust have not yet been discovered.

There are two large areas of outcrops of Archean rocks in North America. The first of these, the Canadian Shield, is located in central Canada on both sides of Hudson Bay. Although in some places the Archean rocks are overlain by younger ones, in most of the territory of the Canadian Shield they make up the surface. The oldest rocks known in this area are marbles, slate and crystalline schists, interbedded with lavas. Initially, limestone and shales were deposited here, subsequently sealed by lavas. Then these rocks were exposed to powerful tectonic movements, which were accompanied by large granite intrusions. Ultimately, the sedimentary rocks underwent severe metamorphism. After a long period of denudation, these highly metamorphosed rocks were brought to the surface in places, but the general background is granites.

Outcrops of Archean rocks are also found in the Rocky Mountains, where they form the crests of many ridges and individual peaks, such as Pikes Peak. Younger rocks there have been destroyed by denudation.

In Europe, Archean rocks are exposed in the Baltic Shield within Norway, Sweden, Finland and Russia. They are represented by granites and highly metamorphosed sedimentary rocks. Similar outcrops of Archean rocks are found in the south and southeast of Siberia, China, western Australia, Africa and northeast South America. The oldest traces of the vital activity of bacteria and colonies of unicellular blue-green algae Collenia were discovered in Archean rocks of southern Africa (Zimbabwe) and Ontario (Canada).

Proterozoic era. At the beginning of the Proterozoic, after a long period of denudation, the land was largely destroyed, certain parts of the continents were submerged and were flooded by shallow seas, and some low-lying basins began to be filled with continental sediments. In North America, the most significant exposures of Proterozoic rocks are found in four areas. The first of them is confined to the southern part of the Canadian Shield, where thick layers of shales and sandstones of the considered age are exposed around Lake. Upper and northeast of the lake. Huron. These rocks are of both marine and continental origin. Their distribution indicates that the position of shallow seas changed significantly throughout the Proterozoic. In many places, marine and continental sediments are interbedded with thick lava strata. At the end of sedimentation, tectonic movements of the earth's crust occurred, Proterozoic rocks underwent folding and large mountain systems were formed. In the foothills east of the Appalachians there are numerous outcrops of Proterozoic rocks. They were originally deposited as layers of limestone and shale, and then during orogenesis (mountain building) they metamorphosed into marble, slate and crystalline schist. In the Grand Canyon region, a thick sequence of Proterozoic sandstones, shales and limestones unconformably overlie Archean rocks. In the northern Rocky Mountains, a sequence of Proterozoic limestones with a thickness of ca. 4600 m. Although the Proterozoic formations in these areas were affected by tectonic movements and were folded and broken by faults, these movements were not intense enough and could not lead to metamorphism of the rocks. Therefore, the original sedimentary textures were preserved there.

In Europe, significant outcrops of Proterozoic rocks are found within the Baltic Shield. They are represented by highly metamorphosed marbles and slates. In northwestern Scotland, a thick sequence of Proterozoic sandstones overlies Archean granites and crystalline schists. Extensive outcrops of Proterozoic rocks are found in western China, in central Australia, southern Africa and central South America. In Australia, these rocks are represented by a thick sequence of unmetamorphosed sandstones and shales, and in eastern Brazil and southern Venezuela - highly metamorphosed slate and crystalline shales.

Fossil blue-green algae Collenia very widespread on all continents in unmetamorphosed limestones of Proterozoic age, where a few fragments of shells of primitive mollusks were also found. However, the remains of animals are very rare, and this indicates that most organisms had a primitive structure and did not yet have hard shells, which are preserved in the fossil state. Although traces of ice ages are recorded for the early stages of Earth's history, extensive glaciation, which had an almost global distribution, is noted only at the very end of the Proterozoic.

Palaeozoic. After the land experienced a long period of denudation at the end of the Proterozoic, some of its territories experienced subsidence and were flooded by shallow seas. As a result of denudation of elevated areas, sedimentary material was carried by water flows into geosynclines, where strata of Paleozoic sedimentary rocks more than 12 km thick accumulated. In North America, at the beginning of the Paleozoic era, two large geosynclines formed. One of them, called the Appalachian, stretches from the North Atlantic Ocean through southeastern Canada and further south to the Gulf of Mexico along the axis of the modern Appalachians. Another geosyncline connected the Arctic Ocean to the Pacific Ocean, passing slightly east of Alaska to the south through eastern British Columbia and western Alberta, then through eastern Nevada, western Utah and southern California. Thus North America was divided into three parts. In certain periods of the Paleozoic, its central regions were partially flooded and both geosynclines were connected by shallow seas. In other periods, as a result of isostatic uplifts of land or fluctuations in the level of the World Ocean, marine regressions occurred, and then terrigenous material washed away from adjacent elevated areas was deposited in geosynclines.

In the Paleozoic, similar conditions existed on other continents. In Europe, huge seas periodically flooded the British Isles, the territories of Norway, Germany, France, Belgium and Spain, as well as a vast area of ​​the East European Plain from the Baltic Sea to Ural mountains. Large outcrops of Paleozoic rocks are also found in Siberia, China and northern India. They are indigenous to most areas of eastern Australia, northern Africa, and northern and central South America.

The Paleozoic era is divided into six periods of unequal duration, alternating with short-term stages of isostatic uplifts or marine regressions, during which sedimentation did not occur within the continents (Fig. 9, 10).

Cambrian period - most early period Paleozoic era, named after the Latin name of Wales (Cumbria), where rocks of this age were first studied. In North America, in the Cambrian, both geosynclines were flooded, and in the second half of the Cambrian, the central part of the continent occupied such a low position that both troughs were connected by a shallow sea and layers of sandstones, shales and limestones accumulated there. A major marine transgression was taking place in Europe and Asia. These parts of the world were largely flooded. The exceptions were three large isolated land masses (the Baltic Shield, the Arabian Peninsula and southern India) and a number of small isolated land areas in southern Europe and southern Asia. Smaller marine transgressions occurred in Australia and central South America. The Cambrian was characterized by rather calm tectonic conditions.

The deposits of this period preserved the first numerous fossils indicating the development of life on Earth. Although no terrestrial plants or animals were recorded, the shallow epicontinental seas and submerged geosynclines were rich in numerous invertebrate animals and aquatic plants. The most unusual and interesting animals of that time were trilobites (Fig. 11), a class of extinct primitive arthropods, which were widespread in the Cambrian seas. Their calcareous-chitinous shells have been found in rocks of this age on all continents. In addition, there were many types of brachiopods (brachiopods), molluscs, and other invertebrates. Thus, all major forms of invertebrate organisms (with the exception of corals, bryozoans and pelecypods) were present in the Cambrian seas.

At the end of the Cambrian period, most of the land experienced uplift and short-term marine regression occurred.

Ordovician period - the second period of the Paleozoic era (named after the Celtic Ordovician tribe that inhabited the territory of Wales). During this period, the continents again experienced subsidence, as a result of which geosynclines and low-lying basins turned into shallow seas. At the end of the Ordovician ca. 70% of North America was flooded by the sea, in which thick layers of limestone and shales were deposited. The sea also covered large areas of Europe and Asia, partly Australia and the central regions of South America.

All Cambrian invertebrates continued to evolve into the Ordovician. In addition, corals, pelecypods (bivalves), bryozoans and the first vertebrates appeared. In Colorado, in Ordovician sandstones, fragments of the most primitive vertebrates were discovered - jawless (ostracoderms), which lacked real jaws and paired limbs, and the front part of the body was covered with bony plates that formed a protective shell.

Based on paleomagnetic studies of rocks, it has been established that throughout most of the Paleozoic, North America was located in the equatorial zone. Fossil organisms and widespread limestones from this time indicate the dominance of warm, shallow seas in the Ordovician. Australia was located near the South Pole, and northwestern Africa was located in the region of the pole itself, which is confirmed by signs of widespread glaciation imprinted in the Ordovician rocks of Africa.

At the end of the Ordovician period, as a result of tectonic movements, continental uplift and marine regression occurred. In some places, the native Cambrian and Ordovician rocks experienced a process of folding, which was accompanied by the growth of mountains. This ancient stage of orogenesis is called the Caledonian folding.

Silurian. For the first time, rocks of this period were also studied in Wales (the name of the period comes from the Celtic tribe of Silures who inhabited this region).

After the tectonic uplifts that marked the end of the Ordovician period, a denudation stage began, and then at the beginning of the Silurian the continents again experienced subsidence, and the seas flooded the low-lying areas. In North America, in the Early Silurian the area of ​​seas decreased significantly, but in the Middle Silurian they occupied almost 60% of its territory. A thick sequence of marine limestones of the Niagara formation was formed, which received its name from the Niagara Falls, the threshold of which it forms. In the Late Silurian, the areas of the seas were greatly reduced. Thick salt-bearing strata accumulated in a strip stretching from modern Michigan to central New York.

In Europe and Asia, the Silurian seas were widespread and occupied almost the same territories as the Cambrian seas. The same isolated massifs as in the Cambrian, as well as significant areas of northern China and Eastern Siberia, remained unflooded. In Europe, thick limestone strata accumulated along the periphery of the southern tip of the Baltic Shield (they are currently partially submerged Baltic Sea). Small seas were common in eastern Australia, northern Africa and central South America.

In the Silurian rocks, in general, the same basic representatives of the organic world were found as in the Ordovician. Land plants had not yet appeared in the Silurian. Among invertebrates, corals have become much more abundant, as a result of whose vital activity massive structures have formed in many areas. Coral reefs. Trilobites, so characteristic of Cambrian and Ordovician rocks, are losing their dominant significance: they are becoming smaller both in quantity and in species. At the end of the Silurian, many large aquatic arthropods called eurypterids, or crustaceans, appeared.

The Silurian period in North America ended without major tectonic movements. However, in Western Europe at this time the Caledonian belt formed. This mountain range extended across Norway, Scotland and Ireland. Orogenesis also occurred in northern Siberia, as a result of which its territory was raised so high that it was never flooded again.

Devonian named after the county of Devon in England, where rocks of this age were first studied. After the denudation break, certain areas of the continents again experienced subsidence and were flooded by shallow seas. In northern England and partly in Scotland, young Caledonides prevented the penetration of the sea. However, their destruction led to the accumulation of thick strata of terrigenous sandstones in the valleys of foothill rivers. This formation of ancient red sandstones is known for its well-preserved fossil fish. Southern England at this time was covered by a sea in which thick layers of limestone were deposited. Large areas in northern Europe were then flooded by seas in which layers of clayey shales and limestones accumulated. When the Rhine cut into these strata in the area of ​​the Eifel massif, picturesque cliffs were formed that rise along the banks of the valley.

The Devonian seas covered many areas of the European part of Russia, southern Siberia and southern China. A vast sea basin flooded central and western Australia. This area has not been covered by the sea since the Cambrian period. In South America, marine transgression extended to some central and western areas. In addition, there was a narrow sublatitudinal trough in the Amazon. Devonian breeds are very widespread in North America. During most of this period, two major geosynclinal basins existed. In the Middle Devonian, marine transgression spread to the territory of the modern river valley. Mississippi, where a multi-layered strata of limestone has accumulated.

In the Upper Devonian, thick horizons of shale and sandstone formed in the eastern regions of North America. These clastic sequences correspond to a stage of mountain building that began at the end of the Middle Devonian and continued until the end of this period. The mountains extended along the eastern flank of the Appalachian geosyncline (from the modern southeastern United States to southeastern Canada). This region was greatly uplifted, its northern part underwent folding, and then extensive granite intrusions occurred there. These granites are used to make up the White Mountains in New Hampshire, Stone Mountain in Georgia, and a number of other mountain structures. Upper Devonian, so-called The Acadian mountains were reworked by denudation processes. As a result, a layered sequence of sandstones has accumulated to the west of the Appalachian geosyncline, the thickness of which in some places exceeds 1500 m. They are widely represented in the region of the Catskill Mountains, hence the name Catskill sandstones. At the same time, mountain building appeared on a smaller scale in some areas of Western Europe. Orogenesis and tectonic uplift of the earth's surface caused marine regression at the end of the Devonian period.

During the Devonian, some important events occurred in the evolution of life on Earth. The first undisputed discoveries of land plants were made in many areas of the globe. For example, in the vicinity of Gilboa (New York), many species of ferns, including giant trees, were found.

Among the invertebrates, sponges, corals, bryozoans, brachiopods and mollusks were widespread (Fig. 12). There were several types of trilobites, although their numbers and species diversity were significantly reduced compared to the Silurian. The Devonian is often called the “age of fish” due to the magnificent flowering of this class of vertebrates. Although primitive jawless animals still existed, more advanced forms began to predominate. Shark-like fish reached a length of 6 m. At this time, lungfishes appeared, in which the swim bladder was transformed into primitive lungs, which allowed them to exist for some time on land, as well as lobe-finned and ray-finned fish. In the Upper Devonian, the first traces of land animals were discovered - large salamander-like amphibians called stegocephalians. Their skeletal features show that they evolved from lungfishes by further improving their lungs and modifying their fins into limbs.

Carboniferous period. After some break, the continents again experienced subsidence and their low-lying areas turned into shallow seas. Thus began the Carboniferous period, which got its name from the widespread occurrence of coal deposits in both Europe and North America. In America, its early stage, characterized by marine conditions, was previously called Mississippian due to the thick layer of limestone that formed within the modern valley of the river. Mississippian, and is now attributed to the lower Carboniferous period.

In Europe, throughout the Carboniferous period, the territories of England, Belgium and northern France were mostly flooded by the sea, in which thick limestone horizons were formed. Some areas of southern Europe and southern Asia were also flooded, where thick layers of shales and sandstones were deposited. Some of these horizons are continental in origin and contain many fossil remains of terrestrial plants and also host coal-bearing strata. Since Lower Carboniferous formations are poorly represented in Africa, Australia and South America, it can be assumed that these territories were located predominantly in subaerial conditions. In addition, there is evidence of widespread continental glaciation there.

In North America, the Appalachian geosyncline was limited from the north by the Acadian Mountains, and from the south, from the Gulf of Mexico, it was penetrated by the Mississippi Sea, which also flooded the Mississippi Valley. Small sea basins occupied some areas in the west of the continent. In the Mississippi Valley region, a multilayered sequence of limestone and shale accumulated. One of these horizons, the so-called Indian limestone, or spergenite, is a good building material. It was used in the construction of many government buildings in Washington.

At the end of the Carboniferous period, mountain building became widespread in Europe. Chains of mountains stretched from southern Ireland through southern England and northern France into southern Germany. This stage of orogenesis is called Hercynian or Variscian. In North America, local uplifts occurred at the end of the Mississippian period. These tectonic movements were accompanied by marine regression, the development of which was also facilitated by glaciations of the southern continents.

In general, the organic world of the Lower Carboniferous (or Mississippian) time was the same as in the Devonian. However, in addition to a greater variety of types of tree ferns, the flora was replenished with tree mosses and calamites (tree-like arthropods of the horsetail class). Invertebrates were mainly represented by the same forms as in the Devonian. During Mississippian times, sea lilies, bottom-dwelling animals similar in shape to a flower, became more common. Among the fossil vertebrates, shark-like fish and stegocephalians are numerous.

At the beginning of the Late Carboniferous (Pennsylvanian in North America), conditions on the continents began to change rapidly. As follows from the significantly wider distribution of continental sediments, the seas occupied smaller spaces. Northwestern Europe spent most of this time in subaerial conditions. The vast epicontinental Ural Sea extended widely across northern and central Russia, and a major geosyncline extended across southern Europe and southern Asia (the modern Alps, Caucasus, and Himalayas lie along its axis). This trough, called the Tethys geosyncline, or sea, existed over a number of subsequent geological periods.

Lowlands stretched across England, Belgium and Germany. Here, as a result of small oscillatory movements of the earth's crust, an alternation of marine and continental environments occurred. As the sea receded, low-lying swampy landscapes with forests of tree ferns, tree mosses and calamites formed. As the seas advanced, sediments covered the forests, compacting woody remains, which turned into peat and then coal. In Late Carboniferous times, cover glaciation spread across the continents of the Southern Hemisphere. In South America, as a result of marine transgression penetrating from the west, most of the territory of modern Bolivia and Peru was flooded.

In early Pennsylvanian time in North America, the Appalachian geosyncline closed, lost contact with the World Ocean, and terrigenous sandstones accumulated in the eastern and central regions of the United States. During the middle and end of this period, the interior of North America (as well as Western Europe) was dominated by lowlands. Here, shallow seas periodically gave way to swamps that accumulated thick peat deposits that later transformed into large coal basins that stretch from Pennsylvania to eastern Kansas. Parts of western North America were flooded by sea during much of this period. Layers of limestone, shale and sandstone were deposited there.

The widespread occurrence of subaerial environments greatly contributed to the evolution of terrestrial plants and animals. Gigantic forests of tree ferns and club mosses covered the vast swampy lowlands. These forests abounded in insects and arachnids. One of the insect species, the largest in geological history, was similar to the modern dragonfly, but had a wingspan of approx. 75 cm. Stegocephalians reached significantly greater species diversity. Some exceeded 3 m in length. In North America alone, more than 90 species of these giant amphibians, which were similar to salamanders, were discovered in swamp sediments of the Pennsylvanian period. The remains of ancient reptiles were found in these same rocks. However, due to the fragmentary nature of the finds, it is difficult to get a complete picture of the morphology of these animals. These primitive forms were probably similar to alligators.

Permian period. Changes in natural conditions that began in the Late Carboniferous were even more pronounced in the Permian period, which ended the Paleozoic era. Its name comes from the Perm region in Russia. At the beginning of this period, the sea occupied the Ural geosyncline - a trough that followed the strike of the modern Ural Mountains. A shallow sea periodically covered some areas of England, northern France and southern Germany, where layered strata of marine and continental sediments accumulated - sandstones, limestones, shales and rock salt. The Tethys Sea existed for most of the period, and a thick sequence of limestones formed in the area of ​​northern India and the modern Himalayas. Thick Permian deposits are present in eastern and central Australia and on the islands of South and Southeast Asia. They are widespread in Brazil, Bolivia and Argentina, as well as in southern Africa.

Many Permian formations in northern India, Australia, Africa and South America are of continental origin. They are represented by compacted glacial deposits, as well as widespread fluvio-glacial sands. In Central and Southern Africa, these rocks begin a thick sequence of continental sediments known as the Karoo Series.

In North America, the Permian seas occupied a smaller area compared to previous Paleozoic periods. The main transgression spread from the western Gulf of Mexico north through Mexico and into the south-central United States. The center of this epicontinental sea was located within the modern state of New Mexico, where a thick sequence of Capitanian limestones formed. Thanks to the activity of groundwater, these limestones acquired a honeycomb structure, especially pronounced in the famous Carlsbad Caverns (New Mexico, USA). Farther east, coastal red shale facies were deposited in Kansas and Oklahoma. At the end of the Permian, when the area occupied by the sea was significantly reduced, thick salt-bearing and gypsum-bearing strata were formed.

At the end of the Paleozoic era, partly in the Carboniferous and partly in the Permian, orogenesis began in many areas. Thick sedimentary rocks of the Appalachian geosyncline were folded and broken by faults. As a result, the Appalachian Mountains were formed. This stage of mountain building in Europe and Asia is called Hercynian or Variscian, and in North America - Appalachian.

The flora of the Permian period was the same as in the second half of the Carboniferous. However, the plants were smaller and not as numerous. This indicates that the Permian climate became colder and drier. The invertebrate animals of the Permian were inherited from the previous period. A great leap occurred in the evolution of vertebrates (Fig. 13). On all continents, continental sediments of Permian age contain numerous remains of reptiles, reaching a length of 3 m. All of these ancestors of Mesozoic dinosaurs were distinguished by a primitive structure and looked like lizards or alligators, but sometimes had unusual features, for example, a high sail-shaped fin extending from the neck to the tail along the back, in Dimetrodon. Stegocephalians were still numerous.

At the end of the Permian period, mountain building, which manifested itself in many areas of the globe against the background of the general uplift of continents, led to such significant changes in the environment that many characteristic representatives of the Paleozoic fauna began to die out. The Permian period was the final stage of the existence of many invertebrates, especially trilobites.

Mesozoic era, divided into three periods, it differed from the Paleozoic in the predominance of continental settings over marine ones, as well as the composition of flora and fauna. Land plants, many groups of invertebrates, and especially vertebrates have adapted to new environments and undergone significant changes.

Triassic opens the Mesozoic era. Its name comes from the Greek. trias (trinity) in connection with the clear three-membered structure of the sediment strata of this period in northern Germany. Red sandstones lie at the base of the sequence, limestones in the middle, and red sandstones and shales at the top. During the Triassic, large areas of Europe and Asia were occupied by lakes and shallow seas. The epicontinental sea covered Western Europe, and its coastline can be traced to England. The above-mentioned stratotype sediments accumulated in this sea basin. The sandstones occurring in the lower and upper parts of the sequence are partly of continental origin. Another Triassic sea basin penetrated into the territory of northern Russia and spread south along the Ural trough. The huge Tethys Sea then covered approximately the same territory as in the Late Carboniferous and Permian times. In this sea, a thick layer of dolomitic limestone has accumulated, which composes the Dolomites of northern Italy. On South central Africa Most of the upper strata of the Karoo continental series are Triassic in age. These horizons are known for the abundance of fossil remains of reptiles. At the end of the Triassic, covers of silts and sands of continental origin formed on the territory of Colombia, Venezuela and Argentina. The reptiles found in these layers show striking similarities to the fauna of the Karoo series of southern Africa.

In North America, Triassic rocks are not as widespread as in Europe and Asia. The products of the destruction of the Appalachians - red continental sands and clays - accumulated in depressions located east of these mountains and experienced subsidence. These deposits, interbedded with lava horizons and sheet intrusions, are faulted and dip to the east. In the Newark Basin in New Jersey and the Connecticut River Valley, they correspond to bedrock of the Newark series. Shallow seas occupied some western areas of North America, where limestones and shales accumulated. Continental sandstones and Triassic shales emerge along the sides of the Grand Canyon (Arizona).

The organic world in the Triassic period was significantly different than in the Permian period. This time is characterized by an abundance of large coniferous trees, the remains of which are often found in Triassic continental deposits. The shales of the Chinle Formation in northern Arizona are loaded with fossilized tree trunks. Weathering of the shale has exposed them and now forms a stone forest. Cycads (or cycadophytes), plants with thin or barrel-shaped trunks and dissected leaves hanging from the top, like those of palm trees, have become widespread. Some cycad species also exist in modern tropical areas. Of the invertebrates, the most common were mollusks, among which ammonites predominated (Fig. 14), which had a vague resemblance to modern nautiluses (or boats) and a multi-chambered shell. There were many species of bivalves. Significant progress has occurred in the evolution of vertebrates. Although stegocephalians were still quite common, reptiles began to predominate, among which many unusual groups appeared (for example, phytosaurs, whose body shape was like that of modern crocodiles, and whose jaws were narrow and long with sharp conical teeth). In the Triassic, true dinosaurs first appeared, evolutionarily more advanced than their primitive ancestors. Their limbs were directed downward, rather than outward (like crocodiles), which allowed them to move like mammals and support their bodies above the ground. Dinosaurs walked on their hind legs, maintaining balance with the help of a long tail (like a kangaroo), and were distinguished by their small stature - from 30 cm to 2.5 m. Some reptiles adapted to life in the marine environment, for example, ichthyosaurs, whose body resembled a shark, and the limbs were transformed into something between flippers and fins, and plesiosaurs, whose torso became flattened, the neck elongated, and the limbs turned into flippers. Both of these groups of animals became more numerous in later stages of the Mesozoic era.

Jurassic period got its name from the Jura Mountains (in northwestern Switzerland), composed of multilayered strata of limestone, shales and sandstones. One of the largest marine transgressions in Western Europe occurred in the Jurassic. A huge epicontinental sea extended over most of England, France, Germany and penetrated into some western regions of European Russia. In Germany there are numerous outcrops of Upper Jurassic lagoonal fine-grained limestones in which unusual fossils have been discovered. In Bavaria, in the famous town of Solenhofen, remains of winged reptiles were found and both known species the first birds.

The Tethys Sea extended from the Atlantic through the southern part of the Iberian Peninsula along Mediterranean Sea and through South and Southeast Asia it reached the Pacific Ocean. Most of northern Asia during this period was located above sea level, although epicontinental seas penetrated into Siberia from the north. Continental sediments of Jurassic age are known in southern Siberia and northern China.

Small epicontinental seas occupied limited areas along the coast of western Australia. In the interior of Australia there are outcrops of Jurassic continental sediments. Most of Africa during the Jurassic period was located above sea level. The exception was its northern outskirts, which were flooded by the Tethys Sea. In South America, an elongated narrow sea filled a geosyncline located approximately on the site of the modern Andes.

In North America, the Jurassic seas occupied very limited areas in the west of the continent. Thick strata of continental sandstones and capping shales accumulated in the Colorado Plateau region, especially north and east of the Grand Canyon. Sandstones were formed from sands that made up the desert dune landscapes of the basins. As a result of weathering processes, sandstones acquired unusual shapes(such as the picturesque peaks in Zion National Park or the Rainbow Bridge National Monument, which is an arch towering 94 m above the canyon floor with a span of 85 m; these attractions are located in Utah). The Morrison Shale deposits are famous for the discovery of 69 species of dinosaur fossils. Fine sediments in this area probably accumulated in swampy lowland conditions.

The flora of the Jurassic period was in general terms similar to that existing in the Triassic. The flora was dominated by cycad and coniferous tree species. For the first time, ginkgos appeared - gymnosperms, broad-leaved woody plants with leaves that fall in autumn (probably a link between gymnosperms and angiosperms). The only species of this family, Ginkgo biloba, has survived to this day and is considered the most ancient representative of the trees, truly a living fossil.

The Jurassic invertebrate fauna is very similar to the Triassic. However, reef-building corals became more numerous, and sea urchins and mollusks became widespread. Many bivalves related to modern oysters appeared. Ammonites were still numerous.

Vertebrates were represented mainly by reptiles, since stegocephalians became extinct at the end of the Triassic. Dinosaurs have reached the culmination of their development. Herbivorous forms such as Apatosaurus and Diplodocus began to move on four limbs; many had long necks and tails. These animals acquired gigantic sizes (up to 27 m in length), and some weighed up to 40 tons. Some representatives of smaller herbivorous dinosaurs, such as stegosaurs, developed a protective shell consisting of plates and spines. Carnivorous dinosaurs, in particular allosaurs, developed large heads with powerful jaws and sharp teeth; they reached a length of 11 m and moved on two limbs. Other groups of reptiles were also very numerous. Plesiosaurs and ichthyosaurs lived in the Jurassic seas. For the first time, flying reptiles appeared - pterosaurs, which developed membranous wings, like bats, and their mass decreased due to tubular bones.

The appearance of birds in the Jurassic - important stage in the development of the animal world. Two bird skeletons and feather imprints were discovered in the lagoonal limestones of Solenhofen. However, these primitive birds still had many features in common with reptiles, including sharp, conical teeth and long tails.

The Jurassic period ended with intense folding, which resulted in the formation of the Sierra Nevada Mountains in the western United States, which extended further north into modern western Canada. Subsequently, the southern part of this folded belt again experienced uplift, which predetermined the structure of modern mountains. On other continents, manifestations of orogenesis in the Jurassic were insignificant.

Cretaceous period. At this time, thick layered strata of soft, weakly compacted white limestone—chalk—accumulated, from which the period took its name. For the first time, such layers were studied in outcrops along the shores of the Pas-de-Calais Strait near Dover (Great Britain) and Calais (France). In other parts of the world, sediments of this age are also called Cretaceous, although other types of rocks are also found there.

During the Cretaceous period, marine transgressions covered large parts of Europe and Asia. In central Europe, the seas filled two sublatitudinal geosynclinal troughs. One of them was located within southeastern England, northern Germany, Poland and western regions of Russia and in the extreme east reached the submeridional Ural trough. Another geosyncline, Tethys, maintained its previous strike in southern Europe and northern Africa and connected to the southern tip of the Ural trough. Further, the Tethys Sea continued in South Asia and east of the Indian Shield it connected with the Indian Ocean. With the exception of the northern and eastern margins, the territory of Asia was not flooded by the sea throughout the entire Cretaceous period, so continental deposits of this time are widespread there. Thick layers of Cretaceous limestone are present in many areas of Western Europe. In the northern regions of Africa, where the Tethys Sea entered, large strata of sandstones accumulated. The sands of the Sahara Desert were formed mainly due to the products of their destruction. Australia was covered by Cretaceous epicontinental seas. In South America, during most of the Cretaceous period, the Andean trough was flooded by the sea. To the east, terrigenous silts and sands with numerous remains of dinosaurs were deposited over a large area of ​​Brazil.

In North America, marginal seas occupied the coastal plains of the Atlantic Ocean and the Gulf of Mexico, where sands, clays and cretaceous limestones accumulated. Another marginal sea was located on the western coast of the mainland within California and reached the southern foot of the revived Sierra Nevada mountains. However, the most recent major marine transgression occurred in western central North America. At this time, a vast geosynclinal trough of the Rocky Mountains formed, and a huge sea spread from the Gulf of Mexico through the modern Great Plains and Rocky Mountains north (west of the Canadian Shield) all the way to the Arctic Ocean. During this transgression, a thick layered sequence of sandstones, limestones and shales was deposited.

At the end of the Cretaceous period, intense orogeny occurred in South and North America and East Asia. In South America, sedimentary rocks accumulated in the Andean geosyncline over several periods were compacted and folded, leading to the formation of the Andes. Similarly, in North America, the Rocky Mountains formed at the site of a geosyncline. Volcanic activity has increased in many areas of the world. Lava flows covered the entire southern part of the Hindustan Peninsula (thus forming the vast Deccan Plateau), and small outpourings of lava took place in Arabia and East Africa. All continents experienced significant uplifts, and regression of all geosynclinal, epicontinental and marginal seas occurred.

The Cretaceous period was marked by several major events in the development of the organic world. The first flowering plants appeared. Their fossil remains are represented by leaves and wood of species, many of which still grow today (for example, willow, oak, maple and elm). The Cretaceous invertebrate fauna is generally similar to the Jurassic. Among vertebrates, the species diversity of reptiles reached a culmination. There were three main groups of dinosaurs. Carnivores with well-developed massive hind limbs were represented by tyrannosaurs, which reached 14 m in length and 5 m in height. A group of bipedal herbivorous dinosaurs (or trachodonts) with wide flattened jaws, reminiscent of a duck's beak, developed. Numerous skeletons of these animals are found in the Cretaceous continental deposits of North America. The third group includes horned dinosaurs with a developed bony shield that protected the head and neck. A typical representative of this group is Triceratops with a short nasal and two long supraorbital horns.

Plesiosaurs and ichthyosaurs lived in the Cretaceous seas, and sea lizards called mosasaurs with an elongated body and relatively small flipper-like limbs appeared. Pterosaurs (flying lizards) lost their teeth and moved better in air space than their Jurassic ancestors. One species of pterosaur, Pteranodon, had a wingspan of up to 8 m.

There are two known species of birds of the Cretaceous period that retained some morphological features of reptiles, for example, conical teeth located in the alveoli. One of them, hesperornis (a diving bird), has adapted to life in the sea.

Although transitional forms more similar to reptiles than to mammals have been known since the Triassic and Jurassic, numerous remains of true mammals were first discovered in continental Upper Cretaceous sediments. The primitive mammals of the Cretaceous period were small in size and somewhat reminiscent of modern shrews.

Widespread mountain building processes on Earth and tectonic uplifts of continents at the end of the Cretaceous period led to such significant changes in nature and climate that many plants and animals became extinct. Among the invertebrates, the ammonites that dominated the Mesozoic seas disappeared, and among the vertebrates, all dinosaurs, ichthyosaurs, plesiosaurs, mosasaurs and pterosaurs disappeared.

Cenozoic era, covering the last 65 million years, is divided into Tertiary (in Russia it is customary to distinguish two periods - Paleogene and Neogene) and Quaternary periods. Although the last one was different short duration(age estimates of its lower boundary range from 1 to 2.8 million years), it played a great role in the history of the Earth, since repeated continental glaciations and the appearance of humans are associated with it.

Tertiary period. At this time, many areas of Europe, Asia and North Africa were covered by shallow epicontinental and deep geosynclinal seas. At the beginning of this period (in the Neogene), the sea occupied southeastern England, northwestern France and Belgium, and a thick layer of sands and clays accumulated there. The Tethys Sea still existed, stretching from the Atlantic to the Indian Ocean. Its waters flooded the Iberian and Apennine peninsulas, the northern regions of Africa, southwest Asia and the north of Hindustan. Thick limestone horizons were deposited in this basin. Much of northern Egypt is composed of nummulitic limestones, which were used as building material in the construction of the pyramids.

At this time almost all Southeast Asia was occupied by marine basins and a small epicontinental sea extended to the southeast of Australia. Tertiary marine basins covered the northern and southern ends of South America, and the epicontinental sea penetrated into eastern Colombia, northern Venezuela, and southern Patagonia. Thick strata of continental sands and silts accumulated in the Amazon basin.

The marginal seas were located on the site of the modern Coastal Plains adjacent to the Atlantic Ocean and the Gulf of Mexico, as well as along the western coast of North America. Thick strata of continental sedimentary rocks, formed as a result of denudation of the revived Rocky Mountains, accumulated on the Great Plains and in the intermountain basins.

In many areas of the globe, active orogenesis occurred in the middle of the Tertiary period. The Alps, Carpathians and Caucasus formed in Europe. In North America, during the final stages of the Tertiary period, the Coast Ranges (within the modern states of California and Oregon) and the Cascade Mountains (within Oregon and Washington) were formed.

The Tertiary period was marked by significant progress in the development of the organic world. Modern plants arose back in the Cretaceous period. Most tertiary invertebrates were directly inherited from Cretaceous forms. Modern bony fish have become more numerous, and the number and species diversity of amphibians and reptiles have decreased. There was a leap in the development of mammals. From primitive forms similar to shrews and first appearing in the Cretaceous period, many forms originate, dating back to the beginning of the Tertiary period. The most ancient fossil remains of horses and elephants were found in the Lower Tertiary rocks. Carnivores and even-toed ungulates appeared.

The species diversity of animals increased greatly, but many of them became extinct by the end of the Tertiary period, while others (like some Mesozoic reptiles) returned to a marine lifestyle, such as cetaceans and porpoises, whose fins are transformed limbs. Bats were able to fly thanks to a membrane connecting their long fingers. Dinosaurs, which went extinct at the end of the Mesozoic, gave way to mammals, which became the dominant class of animals on land at the beginning of the Tertiary period.

Quaternary period divided into Eopleistocene, Pleistocene and Holocene. The latter began just 10,000 years ago. The modern relief and landscapes of the Earth were mainly formed in the Quaternary period.

Mountain building, which occurred at the end of the Tertiary period, predetermined a significant rise of continents and regression of the seas. The Quaternary period was marked by a significant cooling of the climate and the widespread development of glaciation in Antarctica, Greenland, Europe and North America. In Europe, the center of glaciation was the Baltic Shield, from where the ice sheet extended to southern England, central Germany and central regions Of Eastern Europe. In Siberia, cover glaciation was smaller, mainly limited to foothill areas. In North America, ice sheets covered a vast area, including most of Canada and the northern regions of the United States down to southern Illinois. IN Southern Hemisphere The Quaternary ice sheet is characteristic not only of Antarctica, but also of Patagonia. In addition, mountain glaciation was widespread on all continents.

In the Pleistocene, there are four main stages of intensified glaciation, alternating with interglacial periods, during which natural conditions were close to modern or even warmer. The last ice cover in Europe and North America reached largest sizes 18-20 thousand years ago and finally melted at the beginning of the Holocene.

During the Quaternary period, many tertiary forms of animals became extinct and new ones appeared, adapted to colder conditions. Of particular note are the mammoth and woolly rhinoceros, which inhabited the northern regions in the Pleistocene. In the more southern regions of the Northern Hemisphere, mastodons, saber-toothed tigers, etc. were found. When the ice sheets melted, representatives of the Pleistocene fauna died out and modern animals took their place. Primitive people, in particular Neanderthals, probably existed already during the last interglacial, but modern humans are homo sapiens (Homo sapiens) - appeared only in the last glacial epoch of the Pleistocene, and in the Holocene it spread throughout the globe.

Geological chronology, or geochronology, is based on elucidating the geological history of the best-studied regions, such as Central and Eastern Europe. Based on broad generalizations, comparison of the geological history of various regions of the Earth, patterns of evolution of the organic world, at the end of the last century, at the first International Geological Congresses, the International Geochronological Scale was developed and adopted, reflecting the sequence of divisions of time during which certain complexes of sediments were formed, and the evolution of the organic world . Thus, the international geochronological scale is a natural periodization of the history of the Earth.

Among the geochronological divisions there are: eon, era, period, epoch, century, time. Each geochronological division corresponds to a complex of sediments, identified in accordance with changes in the organic world and called stratigraphic: eonothem, group, system, department, stage, zone. Therefore, a group is a stratigraphic unit, and the corresponding time geochronological unit is an era. Therefore, there are two scales: geochronological and stratigraphic. The first is used when talking about relative time in the history of the Earth, and the second when dealing with sediments, since some geological events occurred in every place on the globe at any time. Another thing is that the accumulation of precipitation was not widespread.

• The Archean and Proterozoic eonothems, covering almost 80% of the Earth's existence, are classified as cryptozoic, since Precambrian formations completely lack skeletal fauna and the paleontological method is not applicable to their dissection. Therefore, the division of Precambrian formations is based primarily on general geological and radiometric data.
• The Phanerozoic eon covers only 570 million years and the division of the corresponding eonothem of sediments is based on a wide variety of numerous skeletal fauna. The Phanerozoic eonothem is divided into three groups: Paleozoic, Mesozoic and Cenozoic, corresponding to major stages of the natural geological history of the Earth, the boundaries of which are marked by rather sharp changes in the organic world.

The names of eonotemes and groups come from Greek words:

• "archeos" - the most ancient, the most ancient;
• "proteros" - primary;
• "paleos" - ancient;
• "mesos" - average;
• "kainos" - new.

The word "cryptos" means hidden, and "phanerozoic" means obvious, transparent, since the skeletal fauna appeared.
The word "zoy" comes from "zoikos" - life. Therefore, the “Cenozoic era” means the era of new life, etc.

Groups are divided into systems, the deposits of which were formed during one period and are characterized only by their own families or genera of organisms, and if these are plants, then by genera and species. Systems have been identified in different regions and at different times since 1822. Currently, 12 systems are recognized, most of whose names come from the places where they were first described. For example, the Jurassic system - from the Jurassic Mountains in Switzerland, the Permian - from the Perm province in Russia, the Cretaceous - from the most characteristic rocks - white writing chalk, etc. The Quaternary system is often called the anthropogenic system, since it is in this age interval that humans appear.

Systems are divided into two or three divisions, which correspond to the early, middle, and late eras. The departments, in turn, are divided into tiers, which are characterized by the presence of certain genera and types of fossil fauna. And finally, the stages are divided into zones, which are the most fractional part of the international stratigraphic scale, to which time corresponds on the geochronological scale. The names of the tiers are usually given by the geographical names of the areas where this tier was identified; for example, Aldanian, Bashkir, Maastrichtian stages, etc. At the same time, the zone is designated according to the most characteristic appearance fossil fauna. The zone, as a rule, covers only a certain part of the region and is developed over a smaller area than the deposits of the stage.

All divisions of the stratigraphic scale correspond to the geological sections in which these divisions were first identified. Therefore, such sections are standard, typical and are called stratotypes, which contain only their own complex of organic remains, which determines the stratigraphic volume of a given stratotype. Determining the relative age of any layers consists of comparing the discovered complex of organic remains in the studied layers with the complex of fossils in the stratotype of the corresponding division of the international geochronological scale, i.e. the age of sediments is determined relative to the stratotype. That is why the paleontological method, despite its inherent shortcomings, remains the most important method for determining the geological age of rocks. Determining the relative age of, for example, Devonian deposits only indicates that these deposits are younger than the Silurian, but older than the Carboniferous. However, it is impossible to establish the duration of the formation of Devonian deposits and give a conclusion about when (in absolute chronology) the accumulation of these deposits occurred. Only methods of absolute geochronology can answer this question.

Tab. 1. Geochronological table

Era	Period	era	Duration, million years	Time from the beginning of the period to the present day, million years	Geological conditions	Vegetable world	Animal world
Cenozoic (time of mammals)	Quaternary	Modern	0,011	0,011	The end of the last ice age. The climate is warm	Decline of woody forms, flourishing of herbaceous forms	Age of Man
		Pleistocene	1	1	Repeated glaciations. Four Ice Ages	Extinction of many plant species	Extinction of large mammals. The Birth of Human Society
	Tertiary	Pliocene	12	13	Mountains continue to rise in western North America. Volcanic activity	Forest decline. Distribution of grasslands. Flowering plants; development of monocots	The emergence of man from apes. Species of elephants, horses, camels, similar to modern ones
		Miocene	13	25	The Sierras and Cascade Mountains were formed. Volcanic activity in the northwestern United States. The climate is cool		The culminating period in the evolution of mammals. The first apes
		Oligocene	11	30	The continents are low. The climate is warm	Maximum distribution of forests. Enhancing the development of monocot flowering plants	Archaic mammals are dying out. The beginning of the development of anthropoids; ancestors of most living mammal genera
		Eocene	22	58	The mountains are washed away. There are no inland seas. The climate is warm		Diverse and specialized placental mammals. Ungulates and predators reach their peak
		Paleocene	5	63			Distribution of archaic mammals
Alpine orogeny (minor fossil destruction)
Mesozoic (time of reptiles)	Chalk		72	135	At the end of the period, the Andes, Alps, Himalayas, and Rocky Mountains are formed. Before this, inland seas and swamps. Deposition of writing chalk, clay shales	The first monocots. The first oak and maple forests. Decline of gymnosperms	Dinosaurs reach highest development and die out. Toothed birds are becoming extinct. The appearance of the first modern birds. Archaic mammals are common
	Yura		46	181	The continents are quite elevated. Shallow seas cover some of Europe and the western United States	The importance of dicotyledons is increasing. Cycadophytes and conifers are common	The first toothed birds. Dinosaurs are large and specialized. Insectivorous marsupials
	Triassic		49	230	Continents are elevated above sea level. Intensive development of arid climate conditions. Widespread continental sediments	The dominance of gymnosperms, already beginning to decline. Extinction of seed ferns	The first dinosaurs, pterosaurs and egg-laying mammals. Extinction of primitive amphibians
Hercynian orogeny (some fossil destruction)
Paleozoic (era of ancient life)	Permian		50	280	The continents are uplifted. The Appalachian Mountains were formed. Dryness is increasing. Glaciation in the Southern Hemisphere	Decline of club mosses and ferns	Many ancient animals are becoming extinct. Animal-like reptiles and insects develop
	Upper and mid carbon		40	320	Continents are low-lying at first. Vast swamps where coal formed	Large forests of seed ferns and gymnosperms	The first reptiles. Insects are common. Distribution of ancient amphibians
	Lower Carboniferous		25	345	The climate is initially warm and humid, later, due to the rise of land, it becomes cooler	Moss mosses and fern-like plants dominate. Gymnosperms are becoming more widespread	Sea lilies reach their highest development. Distribution of ancient sharks
	Devonian		60	405	Inland seas are small. Raising land; development of an arid climate. Glaciation	The first forests. Land plants are well developed. First gymnosperms	The first amphibians. Abundance of lungfish and sharks
	Silur		20	425	Vast inland seas. Low-lying areas become increasingly arid as land rises	The first reliable traces of land plants. Algae dominates	Marine arachnids dominate. The first (wingless) insects. Fish development is enhanced
	Ordovician		75	500	Significant immersion of land. The climate is warm, even in the Arctic	The first land plants probably appear. Abundance of seaweed	The first fish were probably freshwater. Abundance of corals and trilobites. Various shellfish
	Cambrian		100	600	The continents are low-lying and the climate is temperate. The most ancient rocks with abundant fossils	Seaweed	Trilobites and non-cured ones dominate. Origins of most modern animal types
Second great orogeny (significant destruction of fossils)
Proterozoic			1000	1600	Intensive process of sedimentation. Later - volcanic activity. Erosion over large areas. Multiple glaciations	Primitive aquatic plants - algae, mushrooms	Various marine protozoa. By the end of the era - molluscs, worms and other marine invertebrates
First great orogeny (significant destruction of fossils)
Archaea			2000	3600	Significant volcanic activity. Weak sedimentation process. Erosion on large areas	No fossils. Indirect indications of the existence of living organisms in the form of deposits of organic matter in rocks

The problem of determining the absolute age of rocks and the duration of the Earth’s existence has long occupied the minds of geologists, and attempts to solve it have been made many times, using various phenomena and processes. Early ideas about the absolute age of the Earth were curious. A contemporary of M.V. Lomonosov, the French naturalist Buffon, determined the age of our planet at only 74,800 years. Other scientists gave different figures, not exceeding 400-500 million years. It should be noted here that all these attempts were doomed to failure in advance, since they were based on the constancy of the rates of processes that, as is known, changed in the geological history of the Earth. And only in the first half of the 20th century. appeared real opportunity truly measure the absolute age of rocks, geological processes, and the Earth as a planet.

Table 2. Isotopes used to determine absolute age
Parent isotope	Final product	Half-life, billion years
147 Sm	143Nd+He	106
238U	206 Pb+ 8 He	4,46
235 U	208 Pb+ 7 He	0,70
232 Th	208 Pb+ 6 He	14,00
87 Rb	87 Sr+β	48,80
40K	40 Ar+ 40 Ca	1,30
14 C	14N	5730 years