Dividing the history of the earth into eras and periods. Geological history of the earth

The geological history of the Earth is the sequence of events in the development of the Earth as a planet. Among these events are the formation of rocks, the emergence and destruction of landforms, the advance and retreat of the sea, glaciation, the appearance and disappearance of species of living beings. It is studied through rock layers; divided into segments according to the geochronological scale.

The Earth formed about 4.5 billion years ago by accretion from a protoplanetary disk, a disk-shaped mass of gas and dust left over from the formation of the Sun that gave rise to the Solar System. The planet was initially hot thanks to residual heat and frequent asteroid impacts. But eventually its outer layer cooled and turned into the earth's crust. A little later, as a result of a tangential collision with a celestial body the size of Mars and a mass of about 10% of the Earth's, the Moon was formed. As a result, most of the substance of the impacted object and part of the substance of the earth's mantle were thrown into low-Earth orbit. From these fragments, a proto-moon assembled and began to orbit with a radius of about 60,000 km. As a result of the impact, the Earth received a sharp increase in rotation speed (one revolution in 5 hours) and a noticeable tilt of the rotation axis. Degassing and volcanic activity created the first atmosphere on Earth. The condensation of water vapor, as well as ice from comets colliding with the Earth, formed oceans.

Over hundreds of millions of years, the surface of the planet was constantly changing, continents formed and broke apart. They migrated across the surface, sometimes joining together to form supercontinents. About 750 million years ago, the supercontinent Rodinia, the first known, began to break up. Later, 600-540 million years ago, the continents formed Pannotia, and about 250 million years ago - Pangea, which broke up about 180 million years ago.

The modern ice age began about 40 million years ago. The cold intensified at the end of the Pliocene. The polar regions began to undergo repeated cycles of glaciation and melting with a period of 40-100 thousand years. The last ice age of the current ice age ended about 10,000 years ago.

Precambrian

The Precambrian comprises about 90% of geological time. It lasted from the formation of the planet (about 4.6 billion years ago) until the beginning of the Cambrian period (541 million years ago). Includes three eons: Katarchean, Archean and Proterozoic.

Catarchaean Eon

Katarchean - the geological eon preceding the Archean, a time from which sedimentary rocks are unknown. After the Archean episode of melting of the upper mantle and its overheating with the emergence of a magma ocean in the geosphere, the entire pristine surface of the Earth, together with its primary and initially dense lithosphere, very quickly sank into the melts of the upper mantle. This explains the absence of Catarchaea in the geological record.

Katarchean spans the first half a billion years of our planet's existence. Its upper boundary is drawn at 4.0 billion years ago.

In popular literature, there is a widespread idea of ​​violent volcanic and hydrothermal activity on the Earth's surface, which does not correspond to reality.

At that time, there were only landscapes of an inhospitable, harsh and cold desert with a black sky (due to a very rarefied atmosphere), a weakly warming Sun (its luminosity was 25-30% lower than the modern one) and a many times larger disk of the Moon (at that time it was at border of the Roche limit, that is, at a distance of about 17 thousand km from the Earth), on which “seas” did not yet exist.

The relief resembled the meteorite-strewn surface of the Moon, but was smoothed due to strong and almost continuous tidal earthquakes and was composed only of monotonously dark gray primary matter, covered on top with a thick layer of regolith. There were no volcanoes spewing streams of lava, fountains of gases and water vapor onto the surface of the young Earth in those days, just as there was no hydrosphere or dense atmosphere. The same small amounts of gases and water vapor that were released during the fall of planetesimals and fragments of the Proto-Moon were absorbed by the porous regolith.

The day at the beginning of the catarchean lasted 6 hours and was approximately equal to the period of revolution of the Moon, but the latter increased very quickly.

Archean eon

The Archean eon is one of the four main eons in the history of the Earth. Lasted from 4.0 to 2.5 billion years ago. At this time, there was still no oxygen atmosphere on Earth, but the first anaerobic bacteria appeared, which formed many of the existing deposits of minerals: sulfur, graphite, iron and nickel.

The term “Archaean” was proposed in 1872 by the American geologist J. Dana.

The Archean is divided into four eras (from latest to earliest):

Neoarchaean

Mesoarchean

Paleoarchaean

Eoarchaean

Eoarchaean era

Eoarchean - geological era, part of the Archean. Covers time from 4.0 to 3.6 billion years ago. It is located between the Katarchean eon and the Paleoarchean era. It is possible that prokaryotes appeared already at the end of this era. In addition, the most ancient geological rocks belong to the Eoarchean - the Isua formation in Greenland.

Paleoarchean era

Paleoarchean - geological era, part of the Archean. Covers time from 3.6 to 3.2 billion years ago. Dating is purely chronological, not based on stratigraphy. The earliest known form of life belongs to this era (well-preserved remains of bacteria over 3.46 billion years old, Western Australia).

Mesoarchean era

Mesoarchean - geological era, part of the Archean. Covers time from 3.2 to 2.8 billion years ago. Dating is purely chronological, not based on stratigraphy. Fossils found in Australia show that stromatolites were already living on Earth during the Mesoarchean.

Neoarchaean era

Neoarchean - geological era, part of the Archean. Covers time from 2.8 to 2.5 billion years ago. The period is determined only chronometrically (without involving stratigraphic data). Refers to the White Sea cycle, during which the formation of the present continental crust took place. Oxygen photosynthesis first appeared in this era, and became the cause of the oxygen catastrophe that occurred later (in the Paleoproterozoic) due to the toxic release of oxygen into the atmosphere.

Proterozoic eon

The Proterozoic Eon is a geological eon that lasted from 2500 to 542.0 ± 1.0 million years ago. Replaces Archaea. The longest eon in Earth's history.

Paleoproterozoic era

Paleoproterozoic is a geological era, part of the Proterozoic, lasting from 2.5 to 1.6 billion years ago. At this time, the first stabilization of the continents begins. Cyanobacteria, a type of bacteria that uses the biochemical process of photosynthesis to produce energy and oxygen, also evolved during this time.

The most important event of the early Paleoproterozoic was the oxygen catastrophe: a significant increase in the oxygen content in the atmosphere. Before this, almost all life forms were anaerobes, meaning their metabolism depended on forms of cellular respiration that did not require oxygen. Oxygen in large quantities is destructive to most anaerobic bacteria, so at this time most of the living organisms on Earth disappeared. The remaining life forms were either immune to the effects of oxygen or lived in an environment devoid of it.

The Paleoproterozoic is divided into four periods (from earliest to latest):

Siderius

Orosirium

Staterius

Siderian period

Siderian is a geological period, part of the Paleoproterozoic. Covers time from 2.5 to 2.3 billion years ago. Dating is purely chronological, not based on stratigraphy.

The beginning of this period marks the peak of occurrence of banded ferruginous quartzites. Iron-bearing rocks formed under conditions where anaerobic algae produced waste oxygen, which mixed with iron to form magnetite (Fe3O4, iron oxide). This process cleared iron from the oceans. Eventually, when the oceans stopped absorbing oxygen, the process led to the formation of the oxygen-rich atmosphere we have today.

The Huronian glaciation began in the Siderian 2.4 billion years ago and ended at the end of the Rhyasian, 2.1 billion years ago.

Riasi period

Riasia is the second geological period of the Paleoproterozoic era. Lasted from 2300 to 2050 million years BC. e. Dating is purely chronological, not based on stratigraphy.

The Bushveld complex and other similar intrusions are formed.

At the end of the Riassian period (by 2100 million years BC) the Huronian glaciation ends.

Prerequisites for the appearance of a nucleus in organisms appear.

Orosirian period

Orosirium is the third geological period of the Paleoproterozoic era, lasting 2050-1800 million years ago (chronometric dating not based on stratigraphy).

The second half of the period was marked by intense mountain building on almost all continents. It is likely that during the Orosirium, the Earth's atmosphere became oxidizing (oxygen-rich) due to the photosynthetic activity of cyanobacteria.

In Orosiria, the Earth experienced two of the largest known asteroid impacts. At the beginning of the period, 2023 million years ago, a collision with a large asteroid led to the formation of the Vredefort astrobleme. Towards the end of the period, a new blow resulted in the formation of the Sudbury copper-nickel ore basin.

Staterian period

Stateria is the final geological period of the Paleoproterozoic era. Lasted 1800-1600 million years ago (chronometric dating not based on stratigraphy).

During the stateria, nuclear living organisms formed.

The period is characterized by the emergence of new platforms and the final cratonization of fold belts. The supercontinent of Columbia is formed.

Mesoproterozoic era

Mesoproterozoic is a geological era, part of the Proterozoic. Lasted from 1.6 to 1.0 billion years ago.

The Mesoproterozoic is divided into three periods:

Kalimium

Ectasy

Calimian period

The Calimian period is the first period of the Mesoproterozoic era. Lasted 1600-1400 million years ago (chronometric dating not based on stratigraphy).

The period is characterized by the expansion of existing sedimentary covers and the emergence of new continental plates as a result of the deposition of sediments on new cratons.

The supercontinent Columbia broke up about 1,500 million years ago during the Kalimium.

Ectasian period

The Ectasian Period is the second geological period of the Mesoproterozoic era, lasting 1400-1200 million years ago (chronometric dating not based on stratigraphy).

The period received its name due to the ongoing sedimentation and expansion of sedimentary covers.

Fossil red algae, the oldest known multicellular organism, have been discovered in rocks from Canada's Somerset Island dating back 1,200 million years.

Stenian period- the final geological period of the Mesoproterozoic era, lasting 1200-1000 million years ago (chronometric dating not based on stratigraphy).

The name comes from the narrow polymetamorphic belts that formed during this period.

The supercontinent Rodinia formed in Stenia.

The earliest fossil remains of eukaryotes that reproduced sexually belong to this period.

Neoproterozoic era

Neoproterozoic is a geochronological era (the last era of the Proterozoic), which began 1000 million years ago and ended 542 million years ago.

At this time, the ancient supercontinent Rodinia broke up into at least 8 fragments, and therefore the ancient superocean Mirovia ceased to exist. During the cryogeny, the largest glaciation of the Earth occurred - ice reached the equator (Snowball Earth).

The Late Neoproterozoic (Ediacaran) includes the oldest fossil remains of large living organisms, since it was at this time that living organisms began to develop some kind of hard shell or skeleton. Most of the Neoproterozoic fauna cannot be considered the ancestors of modern animals, and establishing their place on the evolutionary tree is very problematic.

The Neoproterozoic is divided into three periods:

Cryogenium

Ediacaran

Thonian period

Thonium is the first geochronological period of the Neoproterozoic. Began 1 billion years BC. e. and ended 850 million years BC. e. During this period, the collapse of the supercontinent Rodinia began.

Cryogenian period

Cryogeny is the second geochronological period of the Neoproterozoic. It began 850 million years ago (purely chronometric dating) and ended about 635 million years ago (stratigraphic dating). According to the “Snowball Earth” hypothesis, the most severe glaciation of the Earth, right up to the equator, occurred at this time.

Ediacaran period

The Ediacaran is the last geological period of the Neoproterozoic, Proterozoic and entire Precambrian, immediately before the Cambrian. Lasted from approximately 635 to 541 million years BC. e. The name of the period is derived from the name of the Ediacaran Uplands in South Australia. The name was officially approved by the International Union of Geological Sciences in March 2004 and announced in May of the same year. Before the official international name was approved, the term “Vendian period” or “Vendian” was used in Russian-language literature. This term was also used in foreign literature (English: Vendian period).

The earth was inhabited by soft-bodied creatures - vendobionts - the first known and widespread multicellular animals.

In the sediments of this period there are much fewer remains of living organisms than in newer rocks, because there were no organisms with a skeleton yet. But quite a lot of prints of non-skeletal creatures have been preserved.

Phanerozoic eon

The Phanerozoic eon is a geological eon that began about 541 million years ago and continues into our time, the time of “manifest” life. This eon began with the Cambrian period, when there was a sharp increase in the number of biological species and organisms with mineral skeletons appeared. The previous part of the geological history of the Earth is called cryptosis, that is, the time of “hidden” life, since very few traces of its manifestation are found.

The Phanerozoic eon is divided into three geological eras (from oldest to youngest):

Paleozoic

Mesozoic

Cenozoic

The Vendian period of the Proterozoic is also sometimes referred to as the Phanerozoic.

The most significant events:

. The "Cambrian explosion" which occurred about 540 million years ago.

The five largest extinctions in Earth's history.

Palaeozoic

Paleozoic era, Paleozoic - the geological era of ancient life on planet Earth. The most ancient era in the Phanerozoic eon, follows the Neoproterozoic era and is replaced by the Mesozoic. The Paleozoic began 541 million years ago and lasted about 290 million years. Consists of the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. The Paleozoic group was first identified in 1837 by the English geologist Adam Sedgwick. At the beginning of the era, the southern continents were united into a single supercontinent Gondwana, and by the end other continents joined it and the supercontinent Pangea was formed. The era began with the Cambrian explosion of taxonomic diversity of living organisms and ended with the Permian mass extinction.

Cambrian period

The Cambrian is the first period of the Paleozoic, as well as the entire Phanerozoic. It began 541 million years ago, ended 485 million years ago, and lasted approximately 56 million years. The Cambrian system was first identified in 1835 by the English. researcher A. Sedgwick and received its name from the Roman name for Wales - Cambria. He identified 3 divisions of the Cambrian. The International Commission on Stratigraphy proposed to introduce a 4th department in 2008.

Ordovician period

The Ordovician period (Ordovician) is the second period of the Paleozoic era. Follows the Cambrian and is replaced by the Silurian period. It began 485 million years ago and lasted 42 million years.

Silurian

The Silurian period is the third geological period of the Paleozoic. It came after the Ordovician and was replaced by the Devonian. It began 443 million years ago and lasted 24 million years. The lower limit of the Silurian is determined by a major extinction event, which resulted in the disappearance of about 60% of marine species, the so-called Ordovician-Silurian extinction. During the time of Charles Lyell (mid-19th century), the Silurian was considered the most ancient geological period.

Devonian

Devonian is the fourth geological period of the Paleozoic. Lasted from 419 to 359 million years ago. Duration - 60 million years. This period is rich in biotic events. Life developed rapidly and developed new ecological niches.

Devonshire, or Devon, is a county in southwestern England, in whose territory geological rocks of this period are common. Although the bedrock that marks the beginning of the Devonian period is quite distinct, its exact dating is ambiguous. The modern figure for the beginning of the Devonian is 419.2 ± 3.2, and for the end - 358.9 ± 0.4 million years ago.

Carboniferous period

The Carboniferous period, abbreviated Carboniferous (C) is a geological period in the Upper Paleozoic 358.9 ± 0.4 - 298.9 ± 0.15 million years ago. Named because of the strong coal formation at this time.

For the first time, the outlines of the greatest supercontinent in the history of the Earth - Pangea - appear. Pangea was formed by the collision of Laurasia (North America and Europe) with the ancient southern supercontinent Gondwana. Shortly before the collision, Gondwana rotated clockwise, so that its eastern part (India, Australia, Antarctica) moved to the south, and its western part (South America and Africa) ended up in the north. As a result of the rotation, a new ocean, Tethys, appeared in the east, and the old one, the Rhea Ocean, closed in the west. At the same time, the ocean between the Baltic and Siberia became smaller and smaller; soon these continents also collided.

Permian period

Permian is a geological period, the last period of the Paleozoic. It began 298.9 ± 0.15 million years ago and ended 252.17 ± 0.06 million years ago, that is, it lasted 47 million years. It is underlain by the Carboniferous system of the Paleozoic and overlain by the Triassic system of the Mesozoic.

Mesozoic era

The Mesozoic is a period of time in the geological history of the Earth from 252 million to 66 million years ago, the second of three eras of the Phanerozoic. It was first isolated in 1841 by British geologist John Phillips.

The Mesozoic is an era of tectonic, climatic and evolutionary activity. The formation of the main contours of modern continents and mountain building on the periphery of the Pacific, Atlantic and Indian oceans is taking place; the division of land facilitated speciation and other important evolutionary events. The climate was warm throughout the entire time period, which also played an important role in the evolution and formation of new animal species. By the end of the era, the bulk of the species diversity of life approached its modern state.

Triassic

Triassic period - geological period, the first stage of the Mesozoic; follows the Permian period, precedes the Jurassic. Lasted about 51 million years - from 252 to 201 million years ago. Introduced by F. Alberti in 1834, named for the presence of three layers in the continental Triassic sediments of Western Europe: variegated sandstone, shell limestone and keuper.

Jurassic period

The Jurassic period is the middle period of the Mesozoic. It began 201.3 ± 0.2 million years ago and lasted approximately 56 million years.

For the first time, deposits of this period were described in the Jura (mountains in Switzerland and France), hence the name of the period. The deposits of that time are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates, formed in a wide variety of conditions.

Cretaceous period

The Cretaceous period, or Cretaceous, is the last geological period of the Mesozoic era. Lasted about 79 million years - from 145 to 66 million years ago.

Cenozoic era

The Cenozoic (Cenozoic era) is an era in the geological history of the Earth spanning 66 million years, from the great extinction of species at the end of the Cretaceous period to the present. The Cenozoic period is divided into Paleogene, Neogene and Quaternary periods (Anthropocene). The first two were previously called the Tertiary period.

Paleogene period

Paleogene, Paleogene period - geological period, the first period of the Cenozoic. Began 66.0 million years ago, ended 23.03 million years ago. Lasted 43 million years.

The Paleogene is divided into three eras: the Paleocene with a duration of 10 million years, the Eocene with a duration of 22.1 million years and the Oligocene with a duration of 10.9 million years, which in turn are divided into several centuries.

Paleocene era

Paleocene is the first geological epoch of the Paleogene period. Covers the period from 66.0 to 56.0 million years ago. It is followed by the Eocene.

The Paleocene is divided into three centuries (tiers):

Danish stage (66.0-61.6 million years);

Zealandian Stage (61.6-59.2 million years);

Thanetian stage (59.2-56.0 million years).

At the Paleocene-Eocene boundary, the Late Paleocene thermal maximum occurred.

Eocene epoch

The Eocene is the geological epoch of the Paleogene period, lasting from 56.0 to 33.9 million years ago. Follows the Paleocene and is replaced by the Oligocene.

The name “Eocene” is of Greek origin and was proposed by the Scottish geologist Charles Lyell.

The main event of the Eocene was the appearance of the first "modern" mammals.

The Eocene era is characterized by the development of tropical vegetation. Eocene deposits gave rise to oil, gas, and brown coal deposits.

During this era, significant transgressions of the seas occurred.

Oligocene Epoch

The Oligocene is the last epoch of the Paleogene period, beginning 33.9 million years ago and ending 23.03 million years ago. The Oligocene follows the Eocene and is replaced by the Miocene, which opened the Neogene period.

During the Oligocene, the climate cooled. Mammals developed widely, including early elephants and mesohippus, the ancestors of the modern horse. During this era, more ancient species of mammals became extinct.

Neogene period

Neogene is a geological period, the second period of the Cenozoic. Began 23.03 million years ago, ended only 2.588 million years ago. Thus, it lasted 20.4 million years.

Miocene era

The Miocene is an epoch of the Neogene period that began 23.03 million years ago and ended 5.333 million years ago. The Miocene follows the Oligocene and is replaced by the Pliocene.

The author of the term is the Scottish scientist Charles Lyell, who proposed dividing the Tertiary period into four geological eras (including the Miocene) in the first volume of his book “Fundamentals of Geology” (1830) (his friend W. Viewell also helped him in inventing the term). Whewell) Lyell explains his name by the fact that a minority (18%) of the fossils (which he then studied) from this era can be correlated with modern (new) species.

Pliocene Epoch

The Pliocene is an epoch of the Neogene period that began 5.333 million years ago and ended 2.588 million years ago. The Pliocene epoch replaced the Miocene and gave way to the Pleistocene.

The author of the term is the Scottish scientist Charles Lyell, who proposed dividing the Tertiary period into four geological epochs (including the ancient and modern Pliocene) in the first volume of his book “Principles of Geology” (1830) (he was also helped in the invention of the term by his friend, the Rev. W. Viewell ( Rev. W. Whewell) Lyell explains his name by the fact that the bulk of the fossils (which he then studied) from this era can be correlated with modern (new) species.

It is divided into the following centuries (tiers):

Piacenza (3,600-2,588 million years ago)

Zanklesky (5.333-3.600 million years ago)

This is the shortest geological period, but it was in it that most modern landforms were formed and many significant (from a human point of view) events in the history of the Earth took place, the most important of which were the Ice Age and the appearance of man. The duration of the Quaternary period is so short that conventional methods of relative and isotopic age determination have proven to be insufficiently accurate and sensitive. In such a short time interval, radiocarbon dating and other methods based on the decay of short-lived isotopes are used primarily. The specificity of the Quaternary period in comparison with other geological periods gave rise to a special branch of geology - the Quaternary

The Quaternary period is divided into Pleistocene and Holocene.

Pleistocene era

The Pleistocene is an era of the Quaternary period that began 2.588 million years ago and ended 11.7 thousand years ago.

The Pleistocene epoch replaced the Pliocene and was replaced by the Holocene.

The originator of the term is Scottish geologist and archaeologist Charles Lyell, who proposed dividing the Tertiary period into four geological epochs (including the "Ancient" and "Modern Pliocene") in the first volume of his book "Principles of Geology" (1830). In 1839, he proposed using the term "Pleistocene" for the "new Pliocene".

Eurasia and North America in the Pleistocene had a diverse fauna that included mammoths, woolly rhinoceroses, cave lions, bison, yaks, giant deer, wild horses, camels, bears (both extant and extinct), giant cheetahs, hyenas, ostriches, numerous antelopes. During the late Pleistocene, most of the existing megafauna became extinct. In Australia, marsupial lions and diprotodons - the largest (rhino-sized) marsupials that ever existed on Earth - have disappeared. It is believed that the extinction was caused by primitive hunters at the end of the last ice age, or the extinction occurred as a result of climate change, or a combination of these factors.

Currently, work is underway in Russia and the United States to restore Pleistocene megafauna.

Holocene era

The Holocene is an era of the Quaternary period that lasts for the last 11,700 years until modern times. The boundary between the Holocene and Pleistocene was established at 11,700 ± 99 years ago relative to 2000.

In February 2012, the US National Academy of Sciences published a report confirming the impact of a meteorite in Mexico 13 thousand years ago, causing the abrupt end of the Last Glacial Maximum in the Younger Dryas and mass extinction of fauna.

Paleontologists do not distinguish separate stages of fauna development in the Holocene.

The movement of continents over the past 10,000 years has been insignificant - no more than a kilometer. At the same time, sea level has risen by approximately 135 (+-20) meters from the current level of the world's oceans as a result of melting glaciers. In addition, many areas were pressed down by glaciers, and rose in the late Pleistocene and Holocene by about 180 meters.

Rising sea levels and the temporary pressing down of the land have caused the seas to temporarily encroach into areas that are now far removed from them. Holocene marine fossils are found in areas of Vermont, Quebec, Ontario and Michigan.

In the beginning there was nothing. In the endless space there was only a giant cloud of dust and gases. It can be assumed that from time to time spaceships carrying representatives of the universal mind rushed through this substance at great speed. The humanoids looked boredly out the windows and did not even remotely realize that in a few billion years intelligence and life would arise in these places.

The gas and dust cloud transformed over time into the Solar System. And after the star appeared, the planets appeared. One of them was our native Earth. This happened 4.5 billion years ago. It is from those distant times that the age of the blue planet is counted, thanks to which we exist in this world.

Stages of Earth's development

The entire history of the Earth is divided into two huge stages.. The first stage is characterized by the absence of complex living organisms. There were only single-celled bacteria that settled on our planet about 3.5 billion years ago. The second stage began approximately 540 million years ago. This is the time when living multicellular organisms spread across the Earth. This refers to both plants and animals. Moreover, both seas and land became their habitat. The second period continues to this day, and its crown is man.

Such huge time stages are called eons. Each eon has its own eonothema. The latter represents a certain stage of the geological development of the planet, which is radically different from other stages in the lithosphere, hydrosphere, atmosphere, and biosphere. That is, each eonoteme is strictly specific and not similar to others.

There are 4 eons in total. Each of them, in turn, is divided into eras of the Earth, and those are divided into periods. From this it is clear that there is a strict gradation of large time intervals, and the geological development of the planet is taken as the basis.

Katarhey

The oldest eon is called Katarchean. It began 4.6 billion years ago and ended 4 billion years ago. Thus, its duration was 600 million years. Time is very ancient, so it was not divided into eras or periods. At the time of the Katarchaean there was neither the earth's crust nor the core. The planet was a cold cosmic body. The temperature in its depths corresponded to the melting point of the substance. From above, the surface was covered with regolith, like the lunar surface in our time. The relief was almost flat due to constant powerful earthquakes. Naturally, there was no atmosphere or oxygen.

Archaea

The second eon is called Archean. It began 4 billion years ago and ended 2.5 billion years ago. Thus, it lasted 1.5 billion years. It is divided into 4 eras: Eoarchean, Paleoarchean, Mesoarchean and Neoarchean.

Eoarchaean(4-3.6 billion years) lasted 400 million years. This is the period of formation of the earth's crust. A huge number of meteorites fell on the planet. This is the so-called Late Heavy Bombardment. It was at that time that the formation of the hydrosphere began. Water appeared on Earth. Comets could have brought it in large quantities. But the oceans were still far away. There were separate reservoirs, and the temperature in them reached 90° Celsius. The atmosphere was characterized by a high content of carbon dioxide and a low content of nitrogen. There was no oxygen. At the end of the era, the first supercontinent of Vaalbara began to form.

Paleoarchaean(3.6-3.2 billion years) lasted 400 million years. During this era, the formation of the solid core of the Earth was completed. A strong magnetic field appeared. His tension was half the current one. Consequently, the surface of the planet received protection from the solar wind. This period also saw primitive forms of life in the form of bacteria. Their remains, which are 3.46 billion years old, were discovered in Australia. Accordingly, the oxygen content in the atmosphere began to increase, due to the activity of living organisms. The formation of Vaalbar continued.

Mesoarchean(3.2-2.8 billion years) lasted 400 million years. The most remarkable thing about it was the existence of cyanobacteria. They are capable of photosynthesis and produce oxygen. The formation of the supercontinent has completed. By the end of the era it had split. There was also a huge asteroid impact. The crater from it still exists in Greenland.

Neoarchaean(2.8-2.5 billion years) lasted 300 million years. This is the time of formation of the real earth's crust - tectogenesis. Bacteria continued to develop. Traces of their life were found in stromatolites, whose age is estimated at 2.7 billion years. These lime deposits were formed by huge colonies of bacteria. They were found in Australia and South Africa. Photosynthesis continued to improve.

With the end of the Archean era, the Earth's era continued in the Proterozoic eon. This is a period of 2.5 billion years - 540 million years ago. It is the longest of all the eons on the planet.

Proterozoic

The Proterozoic is divided into 3 eras. The first one is called Paleoproterozoic(2.5-1.6 billion years). It lasted 900 million years. This huge time interval is divided into 4 periods: siderian (2.5-2.3 billion years), rhyasium (2.3-2.05 billion years), orosirium (2.05-1.8 billion years) , stateria (1.8-1.6 billion years).

Siderius notable in the first place oxygen catastrophe. It happened 2.4 billion years ago. Characterized by a dramatic change in the Earth's atmosphere. Free oxygen appeared in it in huge quantities. Before this, the atmosphere was dominated by carbon dioxide, hydrogen sulfide, methane and ammonia. But as a result of photosynthesis and the extinction of volcanic activity at the bottom of the oceans, oxygen filled the entire atmosphere.

Oxygen photosynthesis is characteristic of cyanobacteria, which proliferated on Earth 2.7 billion years ago. Before this, archaebacteria dominated. They did not produce oxygen during photosynthesis. In addition, oxygen was initially consumed in the oxidation of rocks. It accumulated in large quantities only in biocenoses or bacterial mats.

Eventually, a moment came when the surface of the planet became oxidized. And the cyanobacteria continued to release oxygen. And it began to accumulate in the atmosphere. The process accelerated due to the fact that the oceans also stopped absorbing this gas.

As a result, anaerobic organisms died, and they were replaced by aerobic ones, that is, those in which energy synthesis was carried out through free molecular oxygen. The planet was shrouded in the ozone layer and the greenhouse effect decreased. Accordingly, the boundaries of the biosphere expanded, and sedimentary and metamorphic rocks turned out to be completely oxidized.

All these metamorphoses led to Huronian glaciation, which lasted 300 million years. It began in Sideria, and ended at the end of Rhiasia 2 billion years ago. The next period of orosiria is notable for its intense mountain building processes. At this time, 2 huge asteroids fell on the planet. The crater from one is called Vredefort and is located in South Africa. Its diameter reaches 300 km. Second crater Sudbury located in Canada. Its diameter is 250 km.

Last staterian period notable for the formation of the supercontinent Columbia. It includes almost all the continental blocks of the planet. There was a supercontinent 1.8-1.5 billion years ago. At the same time, cells were formed that contained nuclei. That is, eukaryotic cells. This was a very important stage of evolution.

The second era of the Proterozoic is called Mesoproterozoic(1.6-1 billion years). Its duration was 600 million years. It is divided into 3 periods: potassium (1.6-1.4 billion years), exatium (1.4-1.2 billion years), sthenia (1.2-1 billion years).

During the time of Kalimium, the supercontinent Colombia broke up. And during the Exatian era, red multicellular algae appeared. This is indicated by a fossil find on the Canadian island of Somerset. Its age is 1.2 billion years. A new supercontinent, Rodinia, formed in Stenium. It arose 1.1 billion years ago and disintegrated 750 million years ago. Thus, by the end of the Mesoproterozoic there was 1 supercontinent and 1 ocean on Earth, called Mirovia.

The last era of the Proterozoic is called Neoproterozoic(1 billion-540 million years). It includes 3 periods: Thonian (1 billion-850 million years), Cryogenian (850-635 million years), Ediacaran (635-540 million years).

During the Thonian era, the supercontinent Rodinia began to disintegrate. This process ended in cryogeny, and the supercontinent Pannotia began to form from 8 separate pieces of land formed. Cryogeny is also characterized by complete glaciation of the planet (Snowball Earth). The ice reached the equator, and after it retreated, the process of evolution of multicellular organisms sharply accelerated. The last period of the Neoproterozoic Ediacaran is notable for the appearance of soft-bodied creatures. These multicellular animals are called Vendobionts. They were branching tubular structures. This ecosystem is considered the oldest.

Life on Earth originated in the ocean

Phanerozoic

Approximately 540 million years ago, the time of the 4th and last eon began - the Phanerozoic. There are 3 very important eras of the Earth. The first one is called Paleozoic(540-252 million years). It lasted 288 million years. Divided into 6 periods: Cambrian (540-480 million years), Ordovician (485-443 million years), Silurian (443-419 million years), Devonian (419-350 million years), Carboniferous (359-299 million years) and Permian (299-252 million years).

Cambrian considered to be the lifespan of trilobites. These are marine animals similar to crustaceans. Along with them, jellyfish, sponges and worms lived in the seas. Such an abundance of living beings is called Cambrian explosion. That is, there was nothing like this before and suddenly it suddenly appeared. Most likely, it was in the Cambrian that mineral skeletons began to emerge. Previously, the living world had soft bodies. Naturally, they were not preserved. Therefore, complex multicellular organisms of more ancient eras cannot be detected.

The Paleozoic is notable for the rapid expansion of organisms with hard skeletons. From vertebrates, fish, reptiles and amphibians appeared. The plant world was initially dominated by algae. During Silurian plants began to colonize the land. At first Devonian The swampy shores are overgrown with primitive flora. These were psilophytes and pteridophytes. Plants reproduced by spores carried by the wind. Plant shoots developed on tuberous or creeping rhizomes.

Plants began to colonize land during the Silurian period

Scorpions and spiders appeared. The dragonfly Meganeura was a real giant. Its wingspan reached 75 cm. Acanthodes are considered the oldest bony fish. They lived during the Silurian period. Their bodies were covered with dense diamond-shaped scales. IN carbon, which is also called the Carboniferous period, a wide variety of vegetation rapidly developed on the shores of lagoons and in countless swamps. It was its remains that served as the basis for the formation of coal.

This time is also characterized by the beginning of the formation of the supercontinent Pangea. It was fully formed during the Permian period. And it broke up 200 million years ago into 2 continents. These are the northern continent of Laurasia and the southern continent of Gondwana. Subsequently, Laurasia split, and Eurasia and North America were formed. And from Gondwana arose South America, Africa, Australia and Antarctica.

On Permian there were frequent climate changes. Dry times alternated with wet ones. At this time, lush vegetation appeared on the banks. Typical plants were cordaites, calamites, tree and seed ferns. Mesosaur lizards appeared in the water. Their length reached 70 cm. But by the end of the Permian period, early reptiles died out and gave way to more developed vertebrates. Thus, in the Paleozoic, life firmly and densely settled on the blue planet.

The following eras of the Earth are of particular interest to scientists. 252 million years ago came Mesozoic. It lasted 186 million years and ended 66 million years ago. Consisted of 3 periods: Triassic (252-201 million years), Jurassic (201-145 million years), Cretaceous (145-66 million years).

The boundary between the Permian and Triassic periods is characterized by mass extinction of animals. 96% of marine species and 70% of terrestrial vertebrates died. The biosphere was dealt a very strong blow, and it took a very long time to recover. And it all ended with the appearance of dinosaurs, pterosaurs and ichthyosaurs. These sea and land animals were of enormous size.

But the main tectonic event of those years was the collapse of Pangea. A single supercontinent, as already mentioned, was divided into 2 continents, and then broke up into the continents that we know now. The Indian subcontinent also broke away. It subsequently connected with the Asian plate, but the collision was so violent that the Himalayas emerged.

This is what nature was like in the early Cretaceous period

The Mesozoic is notable for being considered the warmest period of the Phanerozoic eon.. This is the time of global warming. It began in the Triassic and ended at the end of the Cretaceous. For 180 million years, even in the Arctic there were no stable pack glaciers. Heat spread evenly across the planet. At the equator, the average annual temperature was 25-30° Celsius. The circumpolar regions were characterized by a moderately cool climate. In the first half of the Mesozoic, the climate was dry, while the second half was characterized by humid climate. It was at this time that the equatorial climate zone was formed.

In the animal world, mammals arose from the subclass of reptiles. This was due to the improvement of the nervous system and brain. The limbs moved from the sides under the body, and the reproductive organs became more advanced. They ensured the development of the embryo in the mother's body, followed by feeding it with milk. Hair appeared, blood circulation and metabolism improved. The first mammals appeared in the Triassic, but they could not compete with dinosaurs. Therefore, for more than 100 million years they occupied a dominant position in the ecosystem.

The last era is considered Cenozoic(beginning 66 million years ago). This is the current geological period. That is, we all live in the Cenozoic. It is divided into 3 periods: Paleogene (66-23 million years), Neogene (23-2.6 million years) and the modern Anthropocene or Quaternary period, which began 2.6 million years ago.

There are 2 main events observed in the Cenozoic. The mass extinction of dinosaurs 65 million years ago and the general cooling of the planet. The death of the animals is associated with the fall of a huge asteroid with a high content of iridium. The diameter of the cosmic body reached 10 km. As a result, a crater was formed Chicxulub with a diameter of 180 km. It is located on the Yucatan Peninsula in Central America.

Surface of the Earth 65 million years ago

After the fall, there was an explosion of enormous force. Dust rose into the atmosphere and blocked the planet from the sun's rays. The average temperature dropped by 15°. The dust hung in the air for a whole year, which led to a sharp cooling. And since the Earth was inhabited by large heat-loving animals, they became extinct. Only small representatives of the fauna remained. It was they who became the ancestors of the modern animal world. This theory is based on iridium. The age of its layer in geological deposits corresponds exactly to 65 million years.

During the Cenozoic, the continents diverged. Each of them formed its own unique flora and fauna. The diversity of marine, flying and terrestrial animals has increased significantly compared to the Paleozoic. They became much more advanced, and mammals took a dominant position on the planet. Higher angiosperms appeared in the plant world. This is the presence of a flower and an ovule. Cereal crops also appeared.

The most important thing in the last era is anthropogen or quaternary period, which began 2.6 million years ago. It consists of 2 eras: the Pleistocene (2.6 million years - 11.7 thousand years) and the Holocene (11.7 thousand years - our time). During the Pleistocene era Mammoths, cave lions and bears, marsupial lions, saber-toothed cats and many other species of animals that became extinct at the end of the era lived on Earth. 300 thousand years ago, man appeared on the blue planet. It is believed that the first Cro-Magnons chose the eastern regions of Africa. At the same time, Neanderthals lived on the Iberian Peninsula.

Notable for the Pleistocene and Ice Ages. For as long as 2 million years, very cold and warm periods of time alternated on Earth. Over the past 800 thousand years, there have been 8 ice ages with an average duration of 40 thousand years. During cold times, glaciers advanced on the continents, and retreated during interglacial periods. At the same time, the level of the World Ocean rose. About 12 thousand years ago, already in the Holocene, the next ice age ended. The climate became warm and humid. Thanks to this, humanity spread throughout the planet.

The Holocene is an interglacial. It has been going on for 12 thousand years. Over the past 7 thousand years, human civilization has developed. The world has changed in many ways. Flora and fauna have undergone significant transformations thanks to human activity. Nowadays, many animal species are on the verge of extinction. Man has long considered himself the ruler of the world, but the era of the Earth has not gone away. Time continues its steady course, and the blue planet conscientiously revolves around the Sun. In a word, life goes on, but the future will show what will happen next.

The article was written by Vitaly Shipunov

Bones of dinosaurs and amazing extinct animals have been found in different eras of 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. Thanks to the release of a large amount 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, the state of the earth’s crust, and underground activity.

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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Archean era. The beginning of this ancient era is considered not the moment of the formation of the Earth, but the time after the formation of the solid earth's crust, when mountains and rocks already existed and the processes of erosion and sedimentation began to take effect. The duration of this era is approximately 2 billion years, i.e. it corresponds to all other eras combined. The Archean era appears to have been characterized by catastrophic and widespread volcanic activity, as well as deep uplifts that culminated in the formation of mountains. The high temperature, pressure and mass movements that accompanied these movements apparently destroyed most of the fossils, but some data about life of those times still remained. In Archeozoic rocks, graphite or pure carbon is found everywhere in scattered form, which probably represents the altered remains of animals and plants. If we accept that the amount of graphite in these rocks reflects the amount of living matter (and this, apparently, is the case), then in the Archean there was probably a lot of this living matter, since there is more carbon in rocks of this age than in coal seams of the Appalachian Basin.

Proterozoic era. The second era, lasting about 1 billion years, was characterized by the deposition of large amounts of sediment and at least one significant glaciation, during which ice sheets extended to latitudes less than 20° from the equator. A very small number of fossils have been found in Proterozoic rocks, which, however, indicate not only the existence of life in this era, but also that evolutionary development had advanced far towards the end of the Proterozoic. Sponge spicules, remains of jellyfish, fungi, algae, brachiopods, arthropods, etc. were found in Proterozoic deposits.

Palaeozoic. Between the deposits of the Upper Proterozoic and the initial layers of the third, Paleozoic era, there is a significant break caused by mountain-building movements. Over 370 million years of the Paleozoic era, representatives of all types and classes of animals appeared, with the exception of birds and mammals. Because different types of animals existed only for certain periods of time, their fossil remains allow geologists to compare sediments of the same age that occur in different places.

• Cambrian period [show] .

  Cambrian period- the most ancient department of the Paleozoic era; is represented by rocks replete with fossils, so that the appearance of the Earth at this time can be reconstructed quite accurately. The forms that lived during this period were so diverse and complex that they must have descended from ancestors that existed at least in the Proterozoic, and possibly in the Archean.

  All modern types of animals, with the exception of chordates, already existed and all plants and animals lived in the sea (the continents, apparently, were lifeless deserts until the late Ordovician or Silurian, when plants moved to land). There were primitive, shrimp-like crustaceans and arachnid-like forms; some of their descendants have survived, almost unchanged, to this day (horseshoe crabs). The seabed was covered with solitary sponges, corals, stalked echinoderms, gastropods and bivalves, primitive cephalopods, brachiopods and trilobites.

  Brachiopods, sessile animals that have bivalve shells and feed on plankton, flourished in the Cambrian and in all other systems of the Paleozoic.

  Trilobites are primitive arthropods with an elongated flat body covered on the dorsal side with a hard shell. Two grooves stretch along the shell, dividing the body into three parts, or lobes. Each body segment, with the exception of the very last, bears a pair of two-branched limbs; one of them was used for walking or swimming and had a gill on it. Most trilobites were 5-7.5 cm in length, but some reached 60 cm.

  In the Cambrian, both unicellular and multicellular algae existed. One of the best preserved collections of Cambrian fossils was collected in the mountains of British Columbia. It includes worms, crustaceans and a transitional form between worms and arthropods, similar to the living Peripatus.

  After the Cambrian, evolution was characterized mainly not by the emergence of completely new types of structure, but by the branching of existing lines of development and the replacement of the original primitive forms with more highly organized ones. Probably, the already existing forms reached such a degree of adaptation to environmental conditions that they acquired a significant advantage over any new, unadapted types.

• Ordovician period [show] .

  During the Cambrian period, the continents began to gradually submerge in water, and in the Ordovician period this subsidence reached its maximum, so that much of the present landmass was covered by shallow seas. These seas were inhabited by huge cephalopods - animals similar to squid and nautilus - with a straight shell from 4.5 to 6 m long and 30 cm in diameter.

  The Ordovician seas were apparently very warm, since corals, which live only in warm waters, spread at this time as far as Lake Ontario and Greenland.

  The first remains of vertebrates were found in Ordovician deposits. These small animals, called scutes, were bottom-dwelling forms, lacking jaws and paired fins (Fig. 1.). Their shell consisted of heavy bony plates on the head and thick scales on the body and tail. Otherwise they were similar to modern lampreys. They apparently lived in fresh water, and their shell served as protection from giant predatory aquatic scorpions called eurypterids, which also lived in fresh water.

• Silurian [show] .

  The Silurian period saw two events of great biological significance: the development of land plants and the appearance of air-breathing animals.

  The first land plants were apparently more similar to ferns than to mosses; Ferns were also the dominant plants in the subsequent Devonian and lower Carboniferous periods.

  The first air-breathing land animals were arachnids, somewhat reminiscent of modern scorpions.

  Continents that had been low-lying in Cambrian and Ordovician times rose, especially in Scotland and northeastern North America, and the climate became much cooler.

• Devonian [show] .

  

  

  

  During the Devonian, the first armored fish gave rise to many different fish, so that this period is often called the “time of the fish.”

  Jaws and paired fins first evolved in armored sharks (Placodermi), which were small, shell-covered freshwater forms. These animals were characterized by a variable number of paired fins. Some had two pairs of fins, corresponding to the fore and hind limbs of higher animals, while others had up to five pairs of additional fins between these two pairs.

  During the Devonian, true sharks appeared in fresh waters, which showed a tendency to move to the ocean and lose their bulky bony shell.

  The ancestors of bony fishes also arose in Devonian freshwater streams; by the middle of this period, they developed a division into three main types: lungfish, lobe-finned and ray-finned. All these fish had lungs and a shell of bony scales. Only a very few lungfishes have survived to this day, and the ray-finned fishes, having undergone a period of slow evolution throughout the remainder of the Paleozoic era and the beginning of the Mesozoic, later, in the Mesozoic, experienced significant divergence and gave rise to modern bony fishes (Teleostei).

  Lobe-finned fish, which were the ancestors of land vertebrates, almost became extinct by the end of the Paleozoic and, as previously believed, completely disappeared at the end of the Mesozoic. However, in 1939 and 1952. Live representatives of lobe-fins, about 1.5 m long, were caught off the east coast of South Africa.

  The upper Devonian was marked by the appearance of the first land vertebrates - amphibians called stegocephalians (meaning "covered-headed"). These animals, whose skulls were covered with a bony shell, are in many respects similar to lobe-finned fish, differing from them mainly in the presence of limbs rather than fins.

  The Devonian is the first period characterized by true forests. During this period, ferns, club mosses, pteridophytes and primitive gymnosperms - the so-called "seed ferns" - flourished. It is believed that insects and millipedes arose in late Devonian times.

• Carboniferous period [show] .

  At this time, large swamp forests were widespread, the remains of which gave rise to the main coal deposits of the world. The continents were covered with low-lying swamps, overgrown with pteridophytes, common ferns, seed ferns and broad-leaved evergreens.

  

  

  The first reptiles, called whole-skulled and similar to the amphibians that preceded them, appeared in the second half of the Carboniferous period, reached their peak in the Permian - the last period of the Paleozoic - and died out at the beginning of the Mesozoic era. It is not clear whether the most primitive reptile known to us, Seymouria (named after the city in Texas near which its fossil remains were found), was an amphibian ready to turn into a reptile, or a reptile that had just crossed the border separating it from amphibians .

  One of the main differences between amphibians and reptiles is the structure of the eggs they lay. Amphibians lay their eggs, covered with a gelatinous shell, in water, and reptiles lay their eggs, covered with a durable shell, on the ground. Since the eggs of Seymouria have not been preserved, we may never be able to decide to what class this animal should be placed.

  Seymouria was a large, slow-moving, lizard-like form. Its short, stump-like legs extended away from its body in a horizontal direction, like a salamander's, instead of being tightly packed and going straight down, forming column-like supports for the body.

  During the Carboniferous period, two important groups of winged insects appeared - the ancestors of cockroaches, which reached 10 cm in length, and the ancestors of dragonflies, some of which had a wingspan of 75 cm.

• Permian period [show] .

  

  

  The last period of the Paleozoic was characterized by major changes in climate and topography. Continents rose all over the globe, so that the shallow seas that covered the area from Nebraska to Texas dried up, leaving behind a saline desert. At the end of the Permian, widespread folding occurred, known as the Hercynian orogeny, during which a large mountain range rose from Nova Scotia to Alabama. This range was originally higher than the modern Rocky Mountains. At the same time, other mountain ranges were forming in Europe.

  Huge ice sheets spreading from the Antarctic covered most of the southern hemisphere, extending in Africa and Brazil almost to the equator.

  North America was one of the few areas not subject to glaciation at this time, but even here the climate became significantly colder and drier than it had been during most of the Paleozoic era. Many Paleozoic organisms apparently could not adapt to climate change and became extinct during the Hercynian orogeny. Due to the cooling of water and the reduction of space suitable for life as a result of the drying out of shallow seas, even many marine forms became extinct.

  From primitive whole-skulled animals, during the Late Carboniferous and Early Permian times, that group of reptiles developed, from which mammals are believed to have descended in a direct line. These were pelycosaurs - predatory reptiles with a more slender and lizard-like body than those of whole skulls.

  In the Late Permian time, another group of reptiles, the therapsids, developed, probably from pelycosaurs, and had several more characteristics of mammals. One of the representatives of this group, Cynognathus (the “dog-jawed” reptile), was a slender, light animal about 1.5 m long, with a skull intermediate in character between that of a reptile and a mammal. Its teeth, instead of being conical and uniform, as is typical of reptiles, were differentiated into incisors, canines and molars. Since we have no information about the soft parts of the animal, whether it was covered with scales or hair, whether it was warm-blooded or cold-blooded, and whether it suckled its young, we call it a reptile. However, if we had more complete data, it might be considered a very early mammal. Therapsids, widespread in the late Permian, were replaced by many other reptiles at the beginning of the Mesozoic.

Mesozoic era (time of reptiles). The Mesozoic era, which began approximately 230 million years ago and lasted about 167 million years, is divided into three periods:

1. Triassic
2. Jurassic
3. chalky

During the Triassic and Jurassic periods, most of the continental areas were raised above sea level. In the Triassic the climate was dry, but warmer than in the Permian, and in the Jurassic it was warmer and more humid than in the Triassic. The trees of Arizona's famous Stone Forest have been around since the Triassic period.

During the Cretaceous period, the Gulf of Mexico expanded and flooded Texas and New Mexico, and in general the sea gradually advanced onto the continents. In addition, extensive swamps have developed in an area stretching from Colorado to British Columbia. At the end of the Cretaceous period, the interior of the North American continent experienced further subsidence, so that the waters of the Gulf of Mexico basin connected with the waters of the Arctic basin and divided this continent into two parts. The Cretaceous period ended with a large uplift called the Alpine orogeny, during which the Rocky Mountains, Alps, Himalayas and Andes were created and which caused active volcanic activity in western North America.

Evolution of reptiles . The emergence, differentiation and finally extinction of a great variety of reptiles belonging to six main branches is the most characteristic feature of the Mesozoic era [show] .

The most primitive branch includes, in addition to the ancient whole-skulls, turtles that arose in the Permian. Turtles have developed the most complex shell (among terrestrial animals); it consists of plates of epidermal origin fused with the underlying ribs and sternum. With this protective adaptation, both sea and land turtles have survived from pre-dinosaur times, with few structural changes. The legs of turtles, extending from the body in a horizontal direction, which complicates and slows down movement, and their skulls, which do not have holes behind the eye sockets, were inherited from ancient whole-skulls without changes.

The second group of reptiles, which comes with relatively few changes from the ancestral whole-skulled ones, are lizards, the most numerous among living reptiles, as well as snakes. Lizards for the most part have retained a primitive type of movement using horizontally diverging legs, although many of them can run quickly. In most cases they are small, but the Indian monitor reaches 3.6 m in length, and some fossil forms are 7.5 m in length. Mosasaurs of the Cretaceous period were sea lizards that reached 12 m in length; they had a long tail, used for swimming.

During the Cretaceous period, snakes evolved from lizard ancestors. The significant difference between snakes and lizards is not the loss of legs (some lizards also lack legs), but certain changes in the structure of the skull and jaws that allow snakes to open their mouths wide enough to swallow animals larger than themselves.

A representative of an ancient branch that somehow managed to survive to this day in New Zealand is the hatteria (Shpenodon punctatum). It shares several features with its cotylosaurian ancestors; one such sign is the presence of a third eye at the top of the skull.

The main group of Mesozoic reptiles were archosaurs, the only living representatives of which are alligators and crocodiles. At some early point in their evolution, archosaurs, then reaching 1.5 m in length, adapted to walking on two legs. Their front legs shortened, while their hind legs lengthened, became stronger, and greatly changed their shape. These animals rested and walked on all four legs, but in critical circumstances they reared and ran on their two hind legs, using their rather long tail as a balance.

Early archosaurs evolved into many different specialized forms, with some continuing to walk on two legs and others returning to walking on all fours. These descendants include phytosaurs - aquatic, alligator-like reptiles common in the Triassic; crocodiles, which formed in the Jurassic and replaced phytosaurs as aquatic forms, and finally pterosaurs, or flying reptiles, which included animals the size of a robin, as well as the largest animal ever to fly, Pteranodon, with a wingspan of 8 m.

There were two types of flying reptiles; some had a long tail equipped with a steering blade at the end, others had a short tail. Representatives of both types apparently fed on fish and probably flew long distances over water in search of food. Their legs were not adapted for standing, and therefore it is assumed that, like bats, they rested in a suspended state, clinging to some support.

Of all the branches of reptiles, the most famous are dinosaurs, which translated means “terrible lizards.” They were divided into two main types: ornithischians and saurians.

Saurischia (lizard-hipped) first appeared in the Triassic and continued to exist until the Cretaceous. Early lizards were fast, predatory, bipedal, rooster-sized forms that likely preyed on lizards and the primitive mammals that had already emerged. During the Jurassic and Cretaceous periods, this group showed a tendency to increase in size, reaching its highest expression in the giant Cretaceous predator Tyrannosaurus. Other Saurischia, which appeared in Late Triassic times, switched to a plant diet, again began to walk on four legs, and during the Jurassic and Cretaceous gave rise to a number of giant forms that led an amphibious lifestyle. These largest four-legged animals that ever lived include brontosaurus, up to 20 m long, diplodocus, which reached a length of over 25 m, and brachiosaurus, the largest of all, whose weight is estimated at 50 tons.

Another group of dinosaurs, the Ornitischia (ornithischians), were herbivores probably from the very beginning of their evolution. Although some walked on their hind legs, most walked on all four legs. Instead of missing front teeth, they developed a strong horny sheath, similar to a bird's beak, which in some forms was wide and flat, like a duck's (hence the name "duck-billed" dinosaurs). This type is characterized by webbed feet. Other species developed large armor plates that protected them from predatory lizards. The ankylosaur, which is called a “tank reptile,” had a wide, flat body covered with bony plates and large spines protruding from its sides.

Finally, some Cretaceous ornithischians developed bony plates around the head and neck. One of them, Triceratops, had two horns over the eyes and a third over the nasal area - all up to almost 1 m long.

Two other groups of Mesozoic reptiles that differed both from each other and from dinosaurs were the marine plesiosaurs and ichthyosaurs. The first were characterized by an extremely long neck, accounting for more than half the length of the animal. Their body was wide, flat, resembling the body of a turtle, and their tail was short. Plesiosaurs swam with flipper-like limbs. They often reached 13-14 m in length.

Ichthyosaurs (fish lizards) were similar in appearance to fish or whales, with a short neck, a large dorsal fin, and a shark-like tail. They swam using rapid movements of their tails, using their limbs only as controls. It is believed that ichthyosaur cubs were born alive, hatching from an egg in the mother’s body, since adult individuals were too specialized and could not go onto land to lay eggs, and reptile eggs drown in water. The discovery of baby skeletons inside the abdominal cavity of adult fossils supports this theory.

At the end of the Cretaceous, many reptiles became extinct. They obviously could not adapt to the significant changes in environmental conditions caused by the Alpine orogeny. As the climate became colder and drier, many plants that served as food for herbivorous reptiles disappeared. Some herbivorous reptiles were too cumbersome to move on land when the swamps dried up. The smaller, warm-blooded mammals that had already appeared had an advantage in the competition for food, and many of them even fed on reptile eggs. The extinction of many reptiles was probably the result of the combined influence of a number of factors or of a single factor.

Other directions of evolution in the Mesozoic . Although reptiles were the dominant animals in the Mesozoic, many other important organisms also evolved during this time. [show] .

During the Mesozoic, the number and diversity of gastropods and bivalves increased. Sea urchins have reached the highest point of their development.

Mammals arose in the Triassic, and bony fish and birds appeared in the Jurassic.

Most modern insect orders appeared in the early Mesozoic.

During Early Triassic time, the most common plants were seed ferns, cycads and conifers, but by the Cretaceous period many other forms resembling modern species appeared - fig trees, magnolias, palms, maples and oaks.

From Jurassic times, magnificent prints of the most ancient species of birds have been preserved, on which even the outlines of feathers are visible. This creature, called Archeopteryx, was about the size of a crow and had rather weak wings, armed with jaw teeth and a long, reptilian tail covered with feathers.

Fossils of two other birds were found in the Cretaceous deposits - Hesperornis and Ichthyornis. The first is an aquatic diving bird that has lost the ability to fly, and the second is a strong flying bird with reptilian teeth, about the size of a dove.

Modern toothless birds formed at the beginning of the next era.

Cenozoic era (time of mammals). The Cenozoic era can equally rightly be called the time of birds, the time of insects or the time of flowering plants, since the development of all these organisms is no less characteristic of it than the development of mammals. It covers the period from the Alpine mountain formation (about 63 million years ago) to the present day and is divided into two periods - the Tertiary, which lasted about 62 million years, and the Quaternary, which includes the last 1-1.5 million years.

• Tertiary period. This period is divided into five eras: Paleocene, Eocene, Oligocene, Miocene and Pliocene. The rocky mountains, formed at the beginning of the Tertiary period, were already heavily eroded by the Oligocene time, as a result of which the North American continent acquired a gently undulating topography.

  During the Miocene, another series of uplifts created the Sierra Nevada and new ranges in the Rocky Mountains, which created deserts in the west. The climate in the Oligocene was milder than today, so palms spread as far north as Wyoming.

  The uplift, which began in the Miocene, continued into the Pliocene and, combined with the glaciations of Pleistocene time, led to the extinction of many pre-existing mammals and other animals. The final uplift of the Colorado Plateau, which created the Grand Canyon, was almost completed in the short time of the Pleistocene and modern eras.

  The oldest fossil remains of true mammals date back to the Late Triassic, and in Jurassic times there were already four orders of mammals, all of them the size of a rat or a small dog.

  The oldest mammals (monotremes) were oviparous animals, and their only representatives that have survived to this day are the platypus and the spiny echidna living in Australia. Both of these forms have fur and nurse their young with milk, but they also lay eggs, like turtles. The ancestral oviparous mammals must, of course, have been distinct from the specialized platypus and echidna, but the fossil record of these ancient forms is incomplete. Today's living monotremes could survive for so long only because they lived in Australia, where until recently there were no placental mammals, so they had no one to compete with.

  In the Jurassic and Cretaceous, most mammals were already highly enough organized to produce live young, although in the most primitive of them - marsupials - the young are born underdeveloped and must remain for several months in a pouch on the mother's stomach, where the nipples are located. Australian marsupials, like monotremes, did not encounter competition from more adapted placental mammals, while on other continents this competition led to the extinction of marsupials and monotremes; Therefore, in Australia, marsupials, as a result of divergent development, gave rise to many different forms, externally resembling some placentals. There are marsupial mice, shrews, cats, moles, bears and one species of wolf, as well as a number of forms that have no placental parallels, such as kangaroos, wombats and wallabies.

  During the Pleistocene, Australia was home to giant kangaroos and rhino-sized wombats. Opossums are more similar to the primitive ancestral marsupials than any of these more specialized forms; they are the only marsupials found outside of Australia and South America.

  Modern highly organized placental mammals, which include humans, characterized by the birth of live young capable of independent existence, descended from insectivorous arboreal ancestors. Fossils of this ancestral form, found in Cretaceous deposits, show that it was a very small animal, like the living shrew. Some of these ancestral mammals retained an arboreal lifestyle and, through a series of intermediate forms, gave rise to primates - monkeys and humans. Others lived on or underground, and during the Paleocene, from them all other mammals living today evolved.

  Primitive Paleocene mammals had conical reptilian teeth, five-fingered limbs, and a small brain. In addition, they were plantigrade, not digitigrade.

  During the Tertiary period, the evolution of herbaceous plants that served as food and forests that sheltered animals was the most important factor influencing changes in the body structure of mammals. Along with the tendency to increase in size, the development of all mammals showed a bias towards an increase in the relative size of the brain and changes in the teeth and legs. When new, more adapted forms appeared, primitive mammals became extinct.

  Although fossils of both marsupials and placentals were found in the Cretaceous deposits, the discovery of highly developed mammals in the early Tertiary deposits was quite unexpected. Whether they really arose at this time or existed before in mountainous areas and were simply not preserved in the form of fossils is not known.

  In the Paleocene and Eocene, the first predators called creodonts evolved from primitive insectivorous placentals. In the Eocene and Oligocene they were replaced by more modern forms, which over time gave rise to living predators such as cats, dogs, bears, weasels, as well as pinnipeds of the sea - seals and walruses.

  

  One of the most famous fossil predators is the saber-toothed tiger, which only recently became extinct during the Pleistocene. It had extremely long and sharp upper fangs, and the lower jaw could swing down and to the side, so that the fangs pierced the victim like sabers.

  Large herbivorous mammals, most of which have hooves, are sometimes grouped into one group called ungulates. However, they are not a single natural group, but consist of several independent branches, so that the cow and the horse, despite the presence of hooves in both, are no more related to each other than each of them is to the tiger. The molars of ungulates are flattened and enlarged, which makes it easier to grind leaves and grass. Their legs became long and adapted to the fast running needed to escape predators.

  The oldest ungulates, called Condylarthra, appeared in the Paleocene. They had a long body and a long tail, flat grinding molars and short legs ending in five toes with a hoof on each. A group similar to primitive predators, the creodonts, were primitive ungulates called Uintatherians. In the Paleocene and Eocene, some of them reached the size of an elephant, while others had three large horns extending from the top of the head.

  The fossil record of several evolutionary lineages of ungulates - horses, camels and elephants - is so complete that it is possible to trace the entire development of these animals from small, primitive five-toed forms. The main direction of evolution in ungulates was towards an increase in overall body size and a decrease in the number of fingers. Ungulates early split into two groups, one of which is characterized by an even number of digits and includes cows, sheep, camels, deer, giraffe, pigs and hippos. Another group is characterized by an odd number of toes and includes horses, zebras, tapirs and rhinoceroses.

  The development of elephants and their recently extinct relatives - mammoths and mastodons - can be traced back centuries to an Eocene ancestor that was the size of a pig and had no trunk. This primitive form, called Moeritherium, was close to the trunk, from which also branched such dissimilar forms as the hyrax (a small marmot-like animal found in Africa and Asia) and the sea cow.

  Whales and dolphins are descended from Eocene cetacean forms called zeiglodonts, and these latter in turn are believed to have descended from creodonts.

  The evolution of bats can be traced back to winged animals that lived in the Eocene and were descendants of primitive insectivores.

  The evolution of some other mammals - rodents, rabbits and edentates (anteaters, sloths and armadillos) - is less known.

• Quaternary period (time of man). The Quaternary period, which covers the last 1-1.5 million years, is usually divided into two eras - Pleistocene and modern. The latter began approximately 11,000 years ago, with the retreat of the last glacier. The Pleistocene was characterized by four ice ages, separated by intervals when glaciers retreated. At the time of maximum expansion, ice sheets occupied almost 10 million square meters in North America. km, extending south all the way to the Ohio and Missouri rivers. The Great Lakes, which were plowed by moving glaciers, radically changed their shape many times and from time to time connected with the Mississippi. It has been estimated that in the past, when the Mississippi collected water from lakes as far as Duluth in the west and Buffalo in the east, its flow was more than 60 times greater than it is today. During the Pleistocene glaciations, such an amount of water was removed from the sea and converted into ice that the sea level dropped by 60-90 m. This caused the formation of land connections that served as settlement routes for many terrestrial organisms, between Siberia and Alaska in the Bering Strait region and between England and the European mainland.

  Plants and animals of the Pleistocene era were similar to modern ones. It is sometimes difficult to distinguish Pleistocene deposits from Pliocene ones, since the organisms they contain are similar to each other and to modern forms. During the Pleistocene, after the emergence of primitive humans, many mammals became extinct, including the saber-toothed tiger, mammoth, and giant ground sloth. The Pleistocene also saw the extinction of many plant species, especially forest ones, and the appearance of numerous herbaceous forms.

  The fossil record leaves no doubt that living species are descended from pre-existing other species. This chronicle is not equally clear for all lines of evolution. The plant tissues are in most cases too soft to yield good fossil remains, and the intermediate forms which serve as links between the different types of animals were apparently skeletal forms of which no trace remains. For many evolutionary lines, in particular for vertebrates, the successive stages of development are well known. There are gaps in other lines that future paleontologists will have to fill.

The 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

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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