And the universe. For example, the hypotheses of Kant - Laplace, O.Yu. Schmidt, Georges Buffon, Fred Hoyle and others. But most scientists tend to believe that the Earth is about 5 billion years old.

The unified international geochronological scale gives an idea of ​​the events of the geological past in their chronological sequence. Its main divisions are the eras: Archean, Proterozoic, Paleozoic, Mesozoic. Cenozoic. The oldest interval of geological time (Archaean and Proterozoic) is also called the Precambrian. It covers a large period - almost 90% of the whole (the absolute age of the planet, according to modern concepts, is taken to be 4.7 billion years).

Within the eras, smaller time intervals are distinguished - periods (for example, the Paleogene, Neogene and Quaternary in the Cenozoic era).

In the Archean era (from the Greek - original, ancient), crystalline rocks (granites, gneisses, schists) were formed. In this era, powerful mountain-building processes took place. The study of this era allowed geologists to assume the presence of the seas and living organisms in them.

The Proterozoic era (the era of early life) is characterized by rock deposits in which the remains of living organisms are found. During this era, the most stable areas, platforms, formed on the surface of the Earth. Platforms - these ancient cores - became the centers of formation.

The Paleozoic era (the era of ancient life) is distinguished by several stages of powerful mountain building,. In this era, the Scandinavian mountains, the Urals, Tien Shan, Altai, Appalachians arose. At this time, animal organisms with a solid skeleton appeared. Vertebrates first appeared: fish, amphibians, reptiles. Ground vegetation appeared in the Middle Paleozoic. Tree ferns, club mosses, and others served as material for the formation of coal deposits.

The Mesozoic era (the era of middle life) is also characterized by intense folding. Mountains formed in areas adjacent to. Reptiles dominated among animals (dinosaurs, proterosaurs, etc.), birds and mammals first appeared. The vegetation consisted of ferns, conifers, angiosperms appeared at the end of the era.

In the Cenozoic era (the era of new life), the modern distribution of continents and oceans takes shape, and intense mountain-building movements take place. Mountain ranges are formed on the shores of the Pacific Ocean, in the south of Europe and Asia (, the Himalayas, the Cordillera Coast Ranges, etc.). At the beginning of the Cenozoic era, the climate was much warmer than today. However, the increase in land area due to the rise of the continents led to a cooling. Extensive ice sheets appeared in the north and. This led to significant changes in the flora and fauna. Many animals have died out. Plants and animals appeared close to modern ones. At the end of this era, man appeared and began to intensively populate the land.

The first three billion years of the development of the Earth led to the formation of land. According to the ideas of scientists, at first there was one continent on Earth, which subsequently split into two, and then another division occurred, and as a result, five continents have formed by today.

The last billion years of the Earth's history is associated with the formation of folded regions. At the same time, several tectonic cycles (epochs) are distinguished in the geological history of the last billion years: Baikal (end of the Proterozoic), Caledonian (early Paleozoic), Hercynian (late Paleozoic), Mesozoic (Mesozoic), Cenozoic or Alpine cycle (from 100 million years to present tense).
As a result of all the above processes, the Earth acquired a modern structure.

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

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

• The Archean and Proterozoic eonotemes, covering almost 80% of the time of the Earth's existence, are distinguished in the Cryptozoic, since the skeletal fauna is completely absent in the Precambrian formations and the paleontological method is not applicable to their division. Therefore, the division of Precambrian formations is based primarily on general geological and radiometric data.
• The Phanerozoic eon covers only 570 million years, and the division of the corresponding eonoteme of deposits is based on a wide variety of numerous skeletal fauna. The Phanerozoic eonoteme is subdivided into three groups: Paleozoic, Mesozoic and Cenozoic, corresponding to major stages in the natural geological history of the Earth, the boundaries of which are marked by rather abrupt changes in the organic world.

The names of eonotems and groups come from Greek words:

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

The word "cryptos" means hidden, and "phanerozoic" means explicit, transparent, since the skeletal fauna appeared.
The word "zoi" comes from "zoikos" - life. Therefore, "Cenozoic era" means the era of new life, and so on.

Groups are subdivided into systems, the deposits of which were formed during one period and are characterized only by families or genera of organisms characteristic of them, and if these are plants, then by genera and species. Systems have been identified in different regions and at different times since 1822. At present, 12 systems are distinguished, the names of most of which come from the places where they were first described. For example, the Jurassic system - from the Jura Mountains in Switzerland, the Permian - from the Perm province in Russia, the Cretaceous - according to the most characteristic rocks - white writing chalk, etc. The Quaternary system is often called Anthropogenic, since it is in this age interval that a person appears.

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

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

Tab. 1. Geological table

Era	Period	Epoch	Duration, Ma	Time from the beginning of the period to the present day, million years	Geological conditions	Vegetable world	Animal world
Cenozoic (time of mammals)	Quaternary	Modern	0,011	0,011	End of the last ice age. The climate is warm	The decline of woody forms, the flowering of herbaceous	Age of Man
		Pleistocene	1	1	repeated glaciations. four ice ages	Extinction of many plant species	Extinction of large mammals. The origin of human society
	Tertiary	Pliocene	12	13	The uplift of mountains in the west of North America continues. Volcanic activity	Decay of forests. Spread of meadows. flowering plants; development of monocots	The emergence of man from the great apes. Types of elephants, horses, camels, similar to modern
		Miocene	13	25	The Sierras and the Cascade Mountains formed. Volcanic activity in the northwestern United States. The climate is cool		The culminating period in the evolution of mammals. The first great apes
		Oligocene	11	30	The continents are low. The climate is warm	Maximum distribution of forests. Strengthening the development of monocotyledonous flowering plants	Archaic mammals are dying out. The beginning of the development of anthropoids; ancestors of most extant genera of mammals
		Eocene	22	58	The mountains are blurred. There are no inland seas. The climate is warm		Diverse and specialized placental mammals. Ungulates and carnivores flourish
		Paleocene	5	63			Distribution of archaic mammals
Alpine orogeny (minor destruction of fossils)
Mesozoic (time of reptiles)	Chalk		72	135	At the end of the period, the Andes, the Alps, the Himalayas, the Rocky Mountains are formed. Prior to this, inland seas and swamps. Deposition of writing chalk, shale	The first monocots. The first oak and maple forests. Decline of gymnosperms	Dinosaurs reach the highest development and die out. Toothed birds are dying out. Appearance of the first modern birds. Archaic mammals are common
	Yura		46	181	The continents are quite elevated. Shallow seas cover parts of Europe and the western United States	The value of dicots increases. Cycadophytes and conifers are common	The first toothed birds. Dinosaurs are large and specialized. Insectivorous marsupials
	Triassic		49	230	Continents are elevated above sea level. Intensive development of arid climate conditions. Widespread continental deposits	The dominance of the gymnosperms, already beginning to decline. Extinction of seed ferns	The first dinosaurs, pterosaurs and egg-laying mammals. Extinction of primitive amphibians
Hercynian orogeny (some destruction of fossils)
Paleozoic (era of ancient life)	Permian		50	280	Continents are raised. Appalachian mountains formed. Dryness is getting worse. Glaciation in the southern hemisphere	Decline of club mosses and ferns	Many ancient animals are dying out. Animal reptiles and insects develop
	Upper and Middle Carboniferous		40	320	The continents are initially low-lying. Vast swamps in which coal was formed	Large forests of seed ferns and gymnosperms	The first reptiles. Insects are common. Distribution of ancient amphibians
	Lower Carboniferous		25	345	The climate is initially warm and humid, later, due to the rise of the land, it becomes cooler.	Club mosses and fern-like plants dominate. Gymnosperms are spreading more and more	Sea lilies reach their highest development. Distribution of ancient sharks
	Devonian		60	405	Inland seas are small. Land elevation; development of an arid climate. Glaciation	First forests. Land plants are well developed. First gymnosperms	The first amphibians. Abundance of lungfish and sharks
	Silurus		20	425	Vast inland seas. Low-lying areas are getting drier as the land rises	The first reliable traces of land plants. Algae dominate	Marine arachnids dominate. The first (wingless) insects. Increased development of fish
	Ordovician		75	500	Significant land sink. The climate is warm, even in the Arctic	Probably the first land plants appear. Abundance of seaweed	The first fish are probably freshwater. Abundance of corals and trilobites. Various clams
	Cambrian		100	600	The continents are low, the climate is temperate. The most ancient rocks with abundant fossils	Seaweed	Trilobites and lechenopods dominate. The origin of most modern animal phyla
Second great orogeny (significant destruction of fossils)
Proterozoic			1000	1600	Intensive process of sedimentation. Later - volcanic activity. Erosion over large areas. Multiple glaciations	Primitive aquatic plants - algae, fungi	Various marine protozoa. By the end of the era - mollusks, worms and other marine invertebrates
First great mountain building (significant destruction of fossils)
archaeus			2000	3600	Significant volcanic activity. Weak sedimentation process. Erosion on large areas	Fossils are absent. Indirect evidence of the existence of living organisms in the form of deposits of organic matter in rocks

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

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

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

The gas and dust cloud eventually transformed into the solar system. And after the luminary appeared, the planets appeared. One of them was our native Earth. It 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 the Earth's development

The entire history of the Earth is divided into two huge time periods. 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 about 540 million years ago. This is the time when living multicellular organisms settled on 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 steps are called eons. Each eon has its own eonoteme. The latter represents a certain stage in the geological development of the planet, which is fundamentally 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 aeons in total. Each of them, in turn, is divided into eras of the Earth, and those are divided into periods. This shows that there is a rigid gradation of large time intervals, and the geological development of the planet is taken as the basis.

catarchean

The most ancient eon is called Katarchaeus. 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 Katarchean, there was neither the earth's crust nor the core. The planet was a cold cosmic body. The temperature in its bowels 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 and oxygen.

archaeus

The second aeon is called Archaea. 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.

Eoarchean(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. In large quantities, comets could bring it. 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 Vaalbar began to form.

paleoarchaean(3.6-3.2 billion years) lasted 400 million years. In this era, the formation of the solid core of the Earth was completed. There was a strong magnetic field. His tension was half the current. Consequently, the surface of the planet received protection from the solar wind. This period also includes primitive life forms in the form of bacteria. Their remains, which are 3.46 billion years old, have been found 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. Most notable was the existence of cyanobacteria. They are capable of photosynthesis and release oxygen. The formation of a supercontinent has been completed. By the end of the era, it had split. There was also a fall of a huge asteroid. A crater from it still exists on the territory of Greenland.

neoarchean(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 grow. Traces of their life are found in stromatolites, whose age is estimated at 2.7 billion years. These lime deposits were formed by huge colonies of bacteria. They are found in Australia and South Africa. Photosynthesis continued to improve.

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

Proterozoic

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

siderius remarkable in the first place oxygen catastrophe. It happened 2.4 billion years ago. It is characterized by a radical change in the Earth's atmosphere. It contained a large amount of free oxygen. Prior to 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 bred on Earth 2.7 billion years ago. Prior to this, archaebacteria dominated. They do not produce oxygen during photosynthesis. In addition, at first oxygen was spent on the oxidation of rocks. In large quantities, it accumulated only in biocenoses or bacterial mats.

In the end, the moment came when the surface of the planet was oxidized. And the cyanobacteria continued to release oxygen. And it began to accumulate in the atmosphere. The process has 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 enveloped 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 Huron glaciation, which lasted 300 million years. It began in the siderium, and ended at the end of the riasian 2 billion years ago. The next Orosirium period notable for intensive 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 is located in Canada. Its diameter is 250 km.

Last statheric period notable for the formation of the supercontinent Columbia. It included 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 in 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), stenium (1.2-1 billion years).

At the time of the kalimium, the supercontinent Columbia collapsed. And during the time of exatia, 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 the walls. It arose 1.1 billion years ago, and broke up 750 million years ago. Thus, by the end of the Mesoproterozoic, there was 1 supercontinent and 1 ocean on Earth, which was called Mirovia.

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

During the time of Toni, the disintegration of the supercontinent Rodinia began. This process ended in cryogeny, and the Pannotia supercontinent 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 they receded, 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, the Phanerozoic, began. There are 3 very important eras of the Earth here. The first is called Paleozoic(540-252 million years). It lasted 288 million years. It is 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 Ma) and Permian (299-252 Ma).

Cambrian considered the lifetime of trilobites. These are marine animals that look like crustaceans. Together with them, jellyfish, sponges and worms lived in the seas. This 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. They, of course, did not survive. Therefore, complex multicellular organisms of more ancient eras cannot be detected.

The Paleozoic is notable for the rapid spread of organisms with hard skeletons. From vertebrates, fish, reptiles and amphibians appeared. In the plant world, algae predominated at first. During Silurian plants began to colonize the land. At the beginning Devonian swampy shores are overgrown with primitive representatives of the 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 develop land in the Silurian period

There were scorpions, spiders. The real giant was the Meganevra dragonfly. 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. AT carbon, which is also called the Carboniferous period, the most diverse vegetation flourished on the shores of the 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 in 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 South America, Africa, Australia and Antarctica arose from Gondwana.

On the Permian there were frequent climate changes. Dry times gave way to wet ones. At this time, lush vegetation appeared on the banks. Typical plants were cordaites, calamites, tree and seed ferns. Mesosaurus 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 reliably and densely settled on the blue planet.

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

The border between the Permian and the Triassic period is characterized by the mass extinction of animals. 96% of marine species and 70% of terrestrial vertebrates died. A very strong blow was dealt to the biosphere, 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 - the collapse of Pangea. A single supercontinent, as already mentioned, was divided into 2 continents, and then broke up into those continents that we know now. The Indian subcontinent also broke away. Subsequently, it connected with the Asian plate, but the collision was so violent that the Himalayas were created.

Such nature was 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 throughout the planet. At the equator, the average annual temperature corresponded to 25-30 ° Celsius. The polar 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. It was at this time that the equatorial climatic zone was formed.

In the animal world, mammals arose from a subclass of reptiles. This was due to the improvement of the nervous system and brain. The limbs moved from the sides under the body, the reproductive organs became more perfect. They ensured the development of the embryo in the mother's body, followed by feeding it with milk. A woolen cover 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 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: the Paleogene (66-23 million years), the Neogene (23-2.6 million years) and the modern anthropogen or Quaternary period, which began 2.6 million years ago.

There are 2 major events in the Cenozoic. The mass extinction of dinosaurs 65 million years ago and the general cooling on the planet. The death of 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. This resulted in the formation of a crater. Chicxulub with a diameter of 180 km. It is located on the Yucatan Peninsula in Central America.

Earth's surface 65 million years ago

After the fall, there was an explosion of great force. Dust rose into the atmosphere and covered the planet from the sun's rays. The average temperature dropped by 15°. 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 died out. 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 land animals has increased significantly in comparison with the Paleozoic. They have become much more advanced, and mammals have taken the dominant position on the planet. In the plant world, higher angiosperms appeared. This is the presence of a flower and an ovule. There were also cereal crops.

The most important thing in the last era is anthropogen or Quaternary, which began 2.6 million years ago. It consists of 2 epochs: 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 animal species that became extinct at the end of the era lived on Earth. 300 thousand years ago, a man appeared on the blue planet. It is believed that the first Cro-Magnons chose for themselves the eastern regions of Africa. At the same time, Neanderthals lived on the Iberian Peninsula.

Notable for the Pleistocene and Ice Ages. For a whole 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. In cold times, glaciers advanced on the continents, and receded in interglacials. At the same time, the level of the World Ocean was rising. About 12 thousand years ago, already in the Holocene, another ice age ended. The climate became warm and humid. Thanks to this, humanity has settled all over the planet.

The Holocene is an interglacial. It has been going on for 12 thousand years. Human civilization has been developing for the last 7 thousand years. The world has changed in many ways. Significant transformations, thanks to the activities of people, have undergone flora and fauna. Today, many animal species are on the verge of extinction. Man has long considered himself the ruler of the world, but the eras of the Earth have not disappeared. Time continues its steady course, and the blue planet conscientiously revolves around the Sun. In a word, life goes on, but what will happen next - the future will show.

The article was written by Vitaly Shipunov

The Archean era is considered a real record holder in terms of duration, because its duration is about 1 billion years! What is interesting about the longest era, and what processes took place on Earth during this period?

Brief description of the era

Which era was the longest, and what is its contribution to the history of the planet? Scientists have long dubbed the Precambrian period the longest in the history of the Earth. It began with the formation of the planet, which happened about 4.54 billion years ago and continued until the Cambrian period. In total, three eras are distinguished in this huge era: Catarchean, Archean and Proterozoic, but the Archean and Proterozoic are considered unambiguous champions.

In total, the Archaean era lasted about a billion years, and during this time the surface of the planet Earth changed completely. Initially, a dense, solid atmosphere stood above the planet, the surface of the earth was hot to the limit. However, due to continuous rains that have been coming for years and decades, the surface has begun to cool. During the same period, large depressions began to fill with liquid, from which oceans, seas and large rivers later formed.

Of course, during this period there was not and could not be any life. While the planet was undergoing rebirth, numerous chemical processes took place in the ocean and sea depths. Salts, acids and alkalis mixed, ionizing water and creating favorable conditions for the future origin of life on the planet.

First signs of life

The longest era in the history of the Earth was, according to many scientists, the period of the birth of the first life. There was no talk of any reasonableness then, and the archaeological data obtained are not enough to set a specific time frame regarding the origin of the first microorganisms. However, the presence of graphite in the rocks of that period indicates its organic origin. Also, scientists managed to find calcareous formations, which most likely had a biogenic origin.

The end of the Archean period is also marked by another important event - the appearance of the first algae. Eukaryotes are green algae with a formed nucleus. Due to the presence of a nucleus in such organisms, the level of transmission of genetic information has increased. All DNA cells were concentrated in the nuclei of eukaryotes, and it was these plants that laid the foundation for life on the planet.

The first signs of life on the planet were found in simple rocks that are 3.5 billion years old. Of course, these were elementary simple organisms with a short lifespan and the most linear genetic code, but for everything on Earth this was progress. It is clear that it was the biological processes that took place in the Archean period that laid the foundation for the origin of life.

For a long time, the planet Earth adapted its surface and atmosphere for future intelligent life. Scientists know very little about the Archean era, but its colossal duration, coupled with the biological importance for all life on Earth, can hardly be overestimated.

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 the restoration of the history of its development. According to modern cosmogonic concepts, the Earth was formed from the gas and dust matter scattered in the protosolar system. One of the most probable variants of the origin of the Earth is as follows. Initially, the Sun and a flattened rotating circumsolar nebula were formed from an interstellar gas and dust cloud under the influence of, for example, the explosion of a nearby supernova. Next, the evolution of the Sun and the near-solar nebula took place with the transfer of the moment of 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 to planets. After that, a similar process was repeated around the planets, which led to the formation of satellites. This process is believed to have taken about 100 million years.

It is assumed that further, as a result of the differentiation of the Earth's substance under the influence of its gravitational field and radioactive heating, different in chemical composition, state of aggregation and physical properties of the shell - the Earth's geosphere - arose and developed. The heavier material formed a core, probably composed of iron mixed with nickel and sulfur. Somewhat lighter elements remained in the mantle. According to one of the hypotheses, 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 sufficient 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 and dust nebula and stuck together under the influence of mutual attraction. As the planet grew, it warmed up due to the collision of these particles, which reached several hundred kilometers, like modern asteroids, and the release of heat not only by naturally radioactive elements now known to us in the crust, but also by more than 10 radioactive isotopes Al, Be, which have since died out. 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 about 3.8 billion years, the Earth and other terrestrial planets, as well as the Moon, were subjected to increased bombardment by small and large meteorites. The result of this bombardment and an earlier collision of planetesimals could be the release of volatiles and the beginning of the formation of a secondary atmosphere, since the primary one, which consisted of gases captured during the formation of the Earth, most likely quickly dissipated into outer space. A little later, the hydrosphere began to form. The atmosphere and hydrosphere formed in this way were replenished in the process of degassing of the mantle during volcanic activity.

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

This crust, containing in its composition already granites and gneisses, however, 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. This crust, metamorphosed everywhere under conditions of high temperatures and pressures, contains rocks whose textural features indicate accumulation in the aquatic environment, i.e. in this distant epoch the hydrosphere already existed. The appearance of the first crust, similar to the modern one, required the supply of large amounts 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 its constituent rocks, was widespread on the area of ​​modern continents. In our country, for example, it is known on the Kola Peninsula and in Siberia, in particular in the basin of the river. Aldan.

Principles of periodization of the geological history of the Earth

Further events in geologic time are often determined according to relative geochronology, categories "old", "younger". For example, some era is older than some other. Separate segments of geological history are called (in decreasing order of their 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. Stenoy established the law of stratification 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 the formation of layers, and hence the geological events associated with them.

The main method in relative geochronology is the biostratigraphic, or paleontological, method of establishing the relative age and sequence of the 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 one can find the remains of animal or plant organisms. J.B. Lamarck and C. Darwin established that animals and plant organisms in 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 development of the Earth, they were replaced by others, more perfect ones. Thus, according to the remains of earlier living more primitive ancestors found in some layer, one can judge the relatively older age of this layer.

Another method of geochronological separation of rocks, especially important for the separation of igneous formations of the ocean floor, is based on the property of the 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 "inherent" magnetization is retained, and the change in polarity is imprinted in a change in the orientation of the remanent magnetization of the rocks. Currently, a scale for the change of such epochs has been established.

Absolute geochronology - the doctrine 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 the analysis of the ratio of radioactive substances and their decay products in rocks formed in different eras.

The oldest rocks are currently established in West Greenland (3.8 billion years). The oldest age (4.1 - 4.2 Ga) was obtained from zircons from Western Australia, but the zircon here occurs in a redeposited state in Mesozoic sandstones. Taking into account the concept of the simultaneity of the formation of all the 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 assumed to be 4.6 billion years.

In 1881, at the II International Geological Congress in Bologna (Italy), the main divisions of the 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 - the era of new life. In 1887, the Proterozoic, the era of primary life, was singled out from the Archean era. Later the scale was improved. One of the variants of the modern geochronological scale is presented in Table. 8.1. The Archean era is divided into two parts: early (older than 3500 Ma) 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 subdivided into the Paleozoic, Mesozoic and Cenozoic eras and consists of 12 periods.

Table 8.1. Geological scale

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

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

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

ATapxee The still rather thin and plastic crust, under the influence of extension, 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 prevailing greenschist low-temperature metamorphism of basalt breeds). Along with basalts, among the lavas of the lower, most thick part of the section of these belts, there are high-magnesian lavas, indicating a very high degree of partial melting of the mantle substance, which indicates a high heat flow, much higher than the modern one. The development of greenstone belts consisted in a change in the type of volcanism towards an increase in the content of silicon dioxide (SiO 2 ) in it, in compressional deformations and metamorphism of sedimentary-volcanogenic fulfillment, and, finally, in the accumulation of clastic sediments, indicating the formation of a mountainous relief.

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 stage, led to the formation of a mature continental crust over most of the area of ​​modern continents. However, this crust turned out to be insufficiently stable: at the beginning of the Proterozoic era, it experienced crushing. At this time, a planetary network of faults and cracks arose, filled with dikes (plate-like geological bodies). One of them, the Great Dike in Zimbabwe, is over 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) of folded systems that re-soldered the 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 (by the turn of 1.7 billion years ago), a 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 was a single massif - the supercontinent Megagea (large land), which on the other side of the globe was opposed by the ocean - the predecessor of the modern Pacific Ocean - Megathalassa (large 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 the beginning of the 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, a radical change in the composition of the atmosphere began: under the influence of plant life, free oxygen appeared in it, while the Catharchean 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) Megagea 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 divided the continents of North America, Eastern Europe, East Asia and the largest fragment of Megagea - the southern supercontinent Gondwana. The central parts of these belts developed on the oceanic crust newly formed during rifting, i.e. the belts were 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 water-glacial sediments).

Paleozoic stage The evolution of the earth's crust was characterized by the intensive development of mobile belts - intercontinental and marginal continental (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-shear deformations, granites were introduced into them and on this basis folded mountain systems were formed. This process proceeded unevenly. 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, Takov (from the Takov mountains in the east of the USA) - at the end of the Ordovician, Caledonian ( from the ancient Roman name of Scotland) - at the end of the Silurian, Acadian (Acadia - the ancient name of the northeastern states of the USA) - in the middle of the Devonian, Sudeten - at the end of the Early Carboniferous, Saal (from the Saale River in Germany) - in the middle of the early Permian. The first three tectonic epochs of the Paleozoic are often combined into the Caledonian era of tectogenesis, the last three into the Hercynian or Varisian. In each of the listed tectonic epochs, certain parts of the mobile belts turned into folded mountain structures, and after destruction (denudation) they were part of the foundation of young platforms. But some of them partially experienced activation in subsequent epochs 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, and the latter (after the completion of the development of the Ural-Okhotsk belt) - with the Siberian, Siberian - with the Chinese-Korean. As a result, the supercontinent Laurasia was formed, and the dying off of the western part of the Mediterranean belt led to its unification with the southern supercontinent - Gondwana - into one continental block - Pangea. The eastern part of the Mediterranean belt at the end of the Paleozoic - the beginning of the Mesozoic 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 relief of the Earth, the development of life continued. The first animals appeared as early as the late Proterozoic, and at the very dawn of the Phanerozoic, almost all types of invertebrates existed, but they still lacked the shells or shells that have been known since the Cambrian. In the Silurian (or already in the Ordovician), vegetation began to land on land, and at the end of the Devonian there were forests that 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 isolation of modern continents. At the beginning of the stage, in the Triassic, Pangea still existed, but already in the early Jurassic, 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 merged with the Pacific Ocean (Fig. 8.6); this ocean also included the Central Atlantic. From here, at the end of the Jurassic, the process of moving apart the continents spread to the north, creating the North Atlantic during the Cretaceous period and the early Paleogene, 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 up from the south. This meant the beginning of the disintegration of Gondwana, which existed as a whole throughout the Paleozoic. At the end of the Cretaceous, the North Atlantic joined the South, 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 current one. However, there were no modern mountain systems yet.

From the Late Paleogene (40 million years ago), intensive mountain building began, culminating in the last 5 million years. This stage of the formation of young fold-cover mountain structures, the formation of revived arch-block mountains is distinguished as neotectonic. In fact, the neotectonic stage is a sub-stage of the Mesozoic-Cenozoic stage of the Earth's development, since it was at this stage that the main features of the modern Earth relief 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 began to predominate in the Cenozoic, and man 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 Anthropogene, the high latitudes of both hemispheres were covered by a powerful continental glaciation, the 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 - the beginning of the Permian; both were common within Gondwana.

QUESTIONS FOR SELF-CHECKING

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 the basis of what is the conclusion about its structure made?

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 are 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 take place within it? What is weather and climate?

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

What is the essence of lithospheric 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 current ideas about the origin of the Earth? How was its early formation as a planet?

On the basis of what is the 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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