Modern geological period geography. Geological history of the earth

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Essay

Geochronological table of the Earth

Completed by: Mikhail Konyshev

Introduction

Geochronological scale- a geological time scale of the history of the Earth, used in geology and paleontology, a kind of calendar for periods of time of hundreds of thousands and millions of years.

According to modern generally accepted ideas, the age of the Earth is estimated at 4.5–4.6 billion years. There are no rocks or minerals found on the Earth's surface that could have witnessed the formation of the planet. The maximum age of the Earth is limited by the age of the earliest solid formations in the Solar System - refractory inclusions rich in calcium and aluminum (CAI) from carbonaceous chondrites. The age of CAI from the Allende meteorite, according to the results of modern studies by the U-Pb isotope method, is 4568.5 ± 0.5 million years. This is the best estimate of the age of the Solar System to date. The time of formation of the Earth as a planet may be millions and even many tens of millions of years later than this date.

Subsequent time in the history of the Earth was divided into various time intervals according to the most important events that then occurred.

The boundary between the Phanerozoic eras passes through the largest evolutionary events - global extinctions. The Paleozoic is separated from the Mesozoic by the largest extinction event in Earth history, the Permo-Triassic extinction event. The Mesozoic is separated from the Cenozoic by the Cretaceous-Paleogene extinction event.

History of the creation of the scale

In the second half of the 19th century, at the II-VIII sessions of the International Geological Congress (IGC) in 1881-1900. the hierarchy and nomenclature of most modern geochronological units were adopted. Subsequently, the International Geochronological (Stratigraphic) Scale was constantly refined.

Specific names were given to periods based on various characteristics. Geographical names were most often used. Thus, the name of the Cambrian period comes from the Latin. Cambria - the name of Wales when it was part of the Roman Empire, Devonian - from the county of Devonshire in England, Permian - from the city of Perm, Jurassic - from the Yuram Mountains in Europe. The Vendian (Vmends is the German name for the Slavic people of the Lusatian Sorbs), Ordovician and Silurian (Celtic tribes of the Ordomvics and Silumrians) periods are named in honor of the ancient tribes. Names related to the composition of the rocks were used less frequently. The Carboniferous period is named because of the large number of coal seams, and the Cretaceous period is named because of the widespread occurrence of writing chalk.

Principle of scale construction

geochronological scale earth geology

The geochronological scale was created to determine the relative geological age of rocks. Absolute age, measured in years, is of secondary importance to geologists.

The existence of the Earth is divided into two main intervals (eons): Phanerozoic and Precambrian (Cryptotic) according to the appearance of fossil remains in sedimentary rocks. Cryptozoic is a time of hidden life; only soft-bodied organisms existed in it, leaving no traces in sedimentary rocks. The Phanerozoic began with the appearance on the border of the Ediacaran (Vendian) and Cambrian of many species of mollusks and other organisms, allowing paleontology to subdivide the strata based on finds of fossil flora and fauna.

Another major division of the geochronological scale has its origin in the very first attempts to divide the history of the earth into major time intervals. Then the whole history was divided into four periods: primary, which is equivalent to the Precambrian, secondary - the Paleozoic and Mesozoic, tertiary - the entire Cenozoic without the last Quaternary period. The Quaternary period occupies a special position. This is the shortest period, but many events took place in it, the traces of which are better preserved than others.

Geochronological scale scale diagrams

Three chronograms are presented, reflecting different stages of the history of the earth on different scales.

1. The top diagram covers the entire history of the earth;

2. The second is the Phanerozoic, a time of mass emergence of various forms of life;

3. Bottom - Cenozoic, the period of time after the extinction of the dinosaurs.

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GEOLOGICAL CHRONOLOGY

A very important characteristic of rocks is their age. As was shown above, many properties of rocks, including engineering-geological ones, depend on it. In addition, based on the study, first of all, of the age of rocks, historical geology recreates the patterns of development and formation of the earth's crust. An important section of historical geology is geochronology - the science of the sequence of geological events in time, their duration and subordination, which it establishes by determining the age of rocks based on the use of various methods and geological disciplines. The relative and absolute ages of rocks are distinguished.

When assessing relative age, older and younger rocks are distinguished by highlighting the time of an event in the history of the Earth in relation to the time of another geological event. Relative age is easier to determine for sedimentary rocks when their occurrence is undisturbed (close to horizontal), as well as for volcanic and, less commonly, metamorphic rocks interbedded with them.

The stratigraphic (stratum - layer) method is based on the study of the sequence of occurrence and relationship of layers of sedimentary deposits, based on the principle of superposition: each overlying layer is younger than the lower one.

It is used for strata with undisturbed horizontal occurrence of layers (Fig. 22). This method should be used carefully when the layers are folded; their roofs and bases must first be determined. The layer is young 3 , and layers 1 And 2 - more ancient.

Lithologo — The petrographic method is based on studying the composition and structure of rocks in adjacent well sections and identifying rocks of the same age - correlation of sections . Sedimentary, volcanic and metamorphic rocks of the same facies and age, for example, clays or limestones, basalts or marble, will have similar textural features and composition.

Geochronological scale of the history of life on Earth

Older rocks, as a rule, are more altered and compacted, while younger ones are slightly altered and porous. It is more difficult to use this method for thin continental deposits, the lithological composition of which changes rapidly along strike.

The most important method for determining relative age is paleontological ( biostratigraphic ) method , based on the identification of layers containing various complexes of fossil remains of extinct organisms. The method is based on the principle of evolution : life on Earth develops from simple to complex and does not repeat itself in its development. Science that establishes the pattern of development of life on Earth by studying the remains of fossil animals and plant organisms - fossils ( fossils) contained in sedimentary rocks is called paleontology. The time of formation of a particular rock corresponds to the time of death of organisms whose remains were buried under layers above the accumulated sediments. The paleontological method makes it possible to determine the age of sedimentary rocks in relation to each other, regardless of the nature of the occurrence of layers, and to compare the age of rocks occurring in areas of the earth's crust distant from each other. Each segment of geological time corresponds to a certain composition of life forms or leading organisms (Fig. 23–29). Leading fossil organisms ( forms ) lived for a short period of geological time over vast areas, usually in reservoirs, seas and oceans. Since the second half of the twentieth century. began to actively use the micropaleontological method, including spore — pollen, for studying organisms invisible to the eye. Based on the paleontological method, diagrams of the evolutionary development of the organic world have been drawn up.

Thus, based on the listed methods for determining the relative age of rocks by the end of the 19th century. A geochronological table was compiled, including subdivisions of two scales: stratigraphic and corresponding geochronological.

Stratigraphic division (unit) is a set of rocks that make up a certain unity according to a set of characteristics (features of material composition, organic remains, etc.), which makes it possible to distinguish it in the section and trace its area. Each stratigraphic unit reflects the uniqueness of the natural geological stage of the development of the Earth (or a separate area), expresses a certain geological age and is comparable to a geochronological unit.

Geochronological (geohistorical) scale is a hierarchical system of geochronological (temporal) divisions, equivalent to units of the general stratigraphic scale. Their ratio and division are shown in table. 15.

isolated in the UK, Perm - in Russia, etc. (Table 16).

Absolute age is the duration of existence (life) of a breed, expressed in years - in time intervals equal to the modern astronomical year (in astronomical units). It is based on measuring the content of radioactive isotopes in minerals: 238U, 232Th, 40K, 87Rb, 14C, etc., their decay products and knowledge of the experimentally determined decay rate. The latter is characterized by a half-life – the time during which half of the atoms of a given unstable isotope decay. The half-life varies greatly among different isotopes (Table 17) and determines the possibilities of its use.

Methods for determining absolute age got their name from radioactive decay products, namely: lead (uranium-lead), argon (potassium-argon), strontium (rubidium-strontium), etc. The potassium-argon method is most often used, since the isotope contains 40K in many minerals (mica, amphiboles, feldspars, clay minerals), decays to form 40Ar and has a half-life of 1.25 billion years. Calculations made using this method are often verified using the strontium method. In the minerals listed above, potassium is isomorphically replaced by 87Rb, which, upon decay, turns into the isotope 87Sr. Using 14C, the age of the youngest Quaternary rocks is determined. Knowing how much lead is formed from 1 g of uranium per year, determining their combined content in a given mineral, you can find the absolute age of the mineral and the rock in which it is located.

The use of these methods is complicated by the fact that rocks undergo various events during their “life”: magmatism, metamorphism, and weathering, during which minerals “open up,” change and lose some of the isotopes and decay products they contain.

Therefore, the term “absolute” age used is convenient for use, but is not absolutely accurate for the age of rocks. It would be more correct to use the term “isotopic” age. A systematic correlation is made between the divisions of the relative geochronological table and the absolute age of rocks, which is still being refined and given in tables.

Geologists, civil engineers, and other professionals can obtain information about the age of rocks by studying geological maps or related geological reports. On maps, the age of rocks is shown by letter and color, which are adopted for the corresponding division of the geochronological table. By comparing the relative age of specific rocks shown by letter and color and the absolute age of the unified geochronological table, we can assume the absolute age of the rocks being studied. Civil engineers must have an understanding of the age of rocks and its designation, and also use them when reading geological documentation (maps and sections) compiled when designing buildings and structures.

The Quaternary period is of particular interest (Table 18). Sediments of the Quaternary system cover the entire earth's surface with a continuous cover; their strata contain the remains of ancient man and his household items. In these strata, various deposits (facies) alternate and replace each other in area: eluvial, alluvial , moraine and fluvioglacial, lacustrine — swamp. Deposits of placer gold and other valuable metals are confined to alluvium. Many rocks of the Quaternary system are raw materials for the production of building materials. A large place is occupied by deposits of the cultural layer , resulting from human activity. They are characterized by significant looseness and great heterogeneity. Its presence can complicate the construction of buildings and structures.

Geochronological table- this is one way of representing the stages of development of planet Earth, in particular life on it. The table records eras, which are divided into periods, their age and duration are indicated, and the main aromorphoses of flora and fauna are described.

Often in geochronological tables, earlier, i.e., older, eras are recorded at the bottom, and later, i.e., younger, eras are recorded at the top. Below is data on the development of life on Earth in natural chronological order: from old to new. The tabular form has been omitted for convenience.

Archean era

It began approximately 3500 million (3.5 billion) years ago.

Lasted about 1000 million years (1 billion).

In the Archean era, the first signs of life on Earth appeared - single-celled organisms.

According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean there was the Catarchean era, when there was no life yet.

Proterozoic era

It began approximately 2700 million (2.7 billion) years ago. Lasted for more than 2 billion years.

Proterozoic - the era of early life. Rare and scarce organic remains are found in the layers belonging to this era. However, they belong to all types of invertebrate animals. Also, the first chordates most likely appear - skullless.

Palaeozoic

It began about 570 million years ago and lasted more than 300 million years.

Paleozoic - ancient life. Starting with it, the process of evolution is better studied, since the remains of organisms from higher geological layers are more accessible. Hence, it is customary to examine each era in detail, noting changes in the organic world for each period (although both the Archean and the Proterozoic have their own periods).

Cambrian period (Cambrian)

Lasted about 70 million years. Marine invertebrates and algae thrive. Many new groups of organisms appear - the so-called Cambrian explosion occurs.

Ordovician period (Ordovician)

Lasted 60 million years. The heyday of trilobites and crustaceans. The first vascular plants appear.

Silurian (30 Ma)

• Coral blossom.
• The appearance of scutes - jawless vertebrates.
• The appearance of psilophyte plants coming onto land.

Devonian (60 Ma)

• The flourishing of the coryptaceae.
• Appearance of lobe-finned fishes and stegocephali.
• Distribution of higher spores on land.

Carboniferous period

Lasted about 70 million years.

• The rise of amphibians.
• The appearance of the first reptiles.
• The appearance of flying forms of arthropods.
• Decline in trilobite numbers.
• Fern blossoming.
• The appearance of seed ferns.

Perm (55 million)

• Distribution of reptiles, emergence of wild-toothed lizards.
• Extinction of trilobites.
• Disappearance of coal forests.
• Distribution of gymnosperms.

Mesozoic era

The era of middle life. It began 230 million years ago and lasted about 160 million years.

Triassic

Duration - 35 million years. The flourishing of reptiles, the appearance of the first mammals and true bony fish.

Jurassic period

Lasted about 60 million years.

• Dominance of reptiles and gymnosperms.
• The appearance of Archeopteryx.
• There are many cephalopods in the seas.

Cretaceous period (70 million years)

• The appearance of higher mammals and true birds.
• Wide distribution of bony fish.
• Reduction of ferns and gymnosperms.
• The emergence of angiosperms.

Cenozoic era

An era of new life. It began 67 million years ago and lasts the same amount.

Paleogene

Lasted about 40 million years.

• The appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
• Rapid flourishing of insects.
• The extinction of large reptiles continues.
• Entire groups of cephalopods are disappearing.
• Dominance of angiosperms.

Neogene (about 23.5 million years)

Dominance of mammals and birds. The first representatives of the genus Homo appeared.

Anthropocene (1.5 Ma)

The emergence of the species Homo Sapiens. The animal and plant world takes on a modern appearance.

New geological period

The International Stratigraphic Committee (ISC) decided at the end of 2000 - consider the time since the second quarter of 2001 as a new geological period within the Cenozoic era. In this regard, our editors have already begun to receive questions:

Why is this necessary?

Why was the Quaternary period so short - only 1-2 million years (according to various estimates), while all previous periods lasted tens of millions of years?

What will the period be called and designated? (Those who have read about the proposed period name ask for an explanation.)

Why exactly from the second quarter, and not from the beginning of some year?

Let's try to answer these questions.

IN AND. Vernadsky believed that human activity was becoming a powerful geological factor, comparable to natural factors. The validity of this became especially obvious towards the end of the twentieth century. The movement of huge masses of rock during mining operations and artificial intervention in the geochemical and hydrogeological regimes of the earth's crust required strict consideration of all this impact. Therefore, the MSC decided to record the state of the earth’s crust at some point in order to, from that moment, keep records of its changes as a result of technogenic impact. It would be logical to make this moment the beginning of 2000 or 2001, but by the beginning of 2000 they did not have time to form a clear idea of ​​the state of the planet’s subsoil as a whole, and by September 2000 it turned out that the necessary documentation was not in time for the beginning of 2001. So the start of the second quarter has been set.

Analyzing the geochronological table, you immediately notice that the duration of eras and periods is gradually decreasing as we approach the present. They wrote about the general acceleration of geological processes, but most likely this is due to the fact that we know more about later geological periods, more traces remain of them, so periodization can be done with greater detail. As for the most recent times, human intervention has indeed accelerated many processes.

Previously, in geology, igneous and metamorphic rocks were considered primary, sedimentary rocks - secondary. When in the middle of the 18th century. younger sedimentary rocks were isolated, they were called tertiary, they included the Paleogene and Neogene, which from half a century ago formed a single tertiary system, which was formed during the Tertiary period of the same name. In 1829, the “youngest” sediments were identified and called Quaternary; Accordingly, the Quaternary period was also identified; its second name is Anthropocene, in Greek giving birth to a person.

Geochronological scale

Therefore, MSC did not suffer for a long time with the name of the new period: without further ado, the period was named fivefold, or man-made(however, the connotation here is somewhat different: not “giving birth to technology,” but “born of technology”). The Quaternary period is designated by the symbol Q (Latin quartus- fourth). They wanted to call the five-fold one by analogy quintus(fifth), but they realized it in time: they would have to denote it with the same letter Q, only, probably, crossed out, like the crossed out P is Paleogene (so as not to be confused with the Permian), the crossed out C is Cambrian (as opposed to the Carboniferous); Anyone who has typed these characters on a typewriter, or especially on a computer, knows how inconvenient it is. They decided to take as a basis not Latin, but English or German and designate the period F ( five or fu..nf), fortunately, there is a precedent: the Cretaceous period is designated by the letter K from German Kreide- chalk.

Now all states are required to submit a report to the MSC every 5 years on the volume of mining work carried out, on the composition of the rocks, in what quantity and from where they were moved, and where they formed the strata of fivefold, or technogenic, deposits. In Russian terminology this is exactly the case - technogenic. Sediments and landforms formed by humans are called anthropogenic, and sediments and forms formed by whatever processes during the Quaternary period, or the Anthropocene, are called anthropogenic. It follows that rocks formed naturally in the fivefold period, without human intervention, can also be called technogenic.

In short, a very serious decision has been made. Time will tell how effective its results will be.

The longest geological period of the planet

Approximately 2500 million years ago, the Archean was replaced by a new eon - the Proterozoic. And it was this that subsequently became the longest geological period in the history of our planet, lasting almost 2000 million years and including three long eras: Paleoproterozoic, Mesoproterozoic and Neoproterozoic, during which significant changes occurred on Earth.

Dividing the history of the Earth into eras and periods

And the first significant event that occurred at the beginning of the longest geological period on the planet, or rather in the Paleoproterozoic era, the Siderian period, that is, about 2.4 billion years ago, was, of course, an oxygen catastrophe, which entailed significant changes in the composition of the atmosphere . Thus, it was in the earliest geological period of the Proterozoic, in connection with the extinction of the activity of oceanic and land volcanoes, that the biochemical composition of the world ocean began to completely change, as a result of which oxygen, already released by existing cyanobacteria, began to be produced even more rapidly, leaving local pockets and oxidizing all around. Upon completion of the oxidation process, the atmosphere finally began to be enriched with free oxygen, and it was this factor that led to a fundamental change in the composition of the atmosphere. It is noteworthy that there is no exact data on its original composition and that everything changed after the oxygen catastrophe is evidenced by the ancient rocks found that never underwent oxidation processes.

After these events, the world was literally “turned” inside out, because if previously it was filled with anaerobic microorganisms that could exist exclusively outside of an oxygen environment, pushing aerobic microorganisms into local pockets, then a gradual increase in the level of oxygen in the atmosphere led to the exact opposite picture. However, this does not mean at all that the rapidly changing atmosphere was even remotely reminiscent of the modern one, because only 400 million years after the start of the oxygen catastrophe, the content of free oxygen in its composition reached ten percent of the volume of O2 that can be observed today (this milestone was called the point Pasteur). It is noteworthy that it was previously believed that this figure was exactly 10 times less, however, as it later turned out, both figures were quite sufficient to ensure the full functioning of rapidly multiplying single-celled organisms. However, these processes entailed another colossal test for the planet - the Ice Age, which developed as a result of the massive absorption of methane by rapidly releasing free oxygen.

And although at that time the luminosity of the Sun for our planet on average increased by as much as 6 percent, it could not warm up due to a shortage of methane, which can produce a powerful greenhouse effect; according to one theory, ice covered the entire globe at that time, literally turning him into a giant snowball. It is noteworthy that by that period the volume of the world ocean that exists in modern times had already been formed, and after the end of the Huronian glaciation period, which occurred approximately 2.1 billion years ago, more complex organisms in the form of sponges and mushrooms began to appear on Earth.

In addition, soil began to actively form; the main role in this process was played by the vital activity of bacteria and single-celled algae, now known as prokaryotes. Another significant event in this era of the Earth’s existence was the first relative stabilization of the continents, as a result of which the once existing super-continent Rodinia began to form, although it was far from the only one in its entire history. The end of the formation of this formation is approximately dated to 1150 million years BC, but by the end of the Proterozoic it collapsed again.

In fact, Rodinia existed for no more than 250 million years and after its collapse, about 8 large fragments remained, which later became the basis for modern continents. During this period, complex organisms already existed on the planet, as evidenced by their numerous remains. Unfortunately, the collapse of the super-continent was not the last test for the Earth of the Paleozoic era, because soon its surface was again bound by ice, which claimed the lives of hundreds of thousands of animals that had appeared by that time.

It is noteworthy that the found remains of animals, most likely killed by the next global cooling, had a solid skeleton. This fact indicates that evolution during the Proterozoic period was striking in the scale of its development.

For ease of study, the history of the development of the Earth is divided into four eras and eleven periods. The two most recent periods are in turn divided into seven systems or eras.

The earth's crust is stratified, i.e. the various rocks that make it up lie in layers on top of each other. As a rule, the age of rocks decreases towards the upper layers. The exception is areas with disturbed layers due to movements of the earth's crust. William Smith in the 18th century noticed that over geological periods of time some organisms made significant advances in their structure.

According to modern estimates, the age of planet Earth is approximately 4.6 - 4.9 10 years. These estimates are based mainly on the study of rocks using radiometric dating methods.

ARCHAY. Not much is known about life in the Archean. The only animal organisms were cellular prokaryotes - bacteria and blue-green algae. The products of the vital activity of these primitive microorganisms are also the oldest sedimentary rocks (stromatolites) - pillar-shaped calcareous formations found in Canada, Australia, Africa, the Urals, and Siberia. Sedimentary rocks of iron, nickel, and manganese have a bacterial basis. Many microorganisms are active participants in the formation of colossal, as yet poorly diluted mineral resources on the bottom of the World Ocean. The role of microorganisms in the formation of oil shale, oil and gas is also great.

Geochronological table of the Earth

Blue-green bacteria quickly spread through the archaea and become masters of the planet. These organisms did not have a separate nucleus, but a developed metabolic system and the ability to reproduce. Blue-greens, in addition, possessed a photosynthetic apparatus. The appearance of the latter was the largest aromorphosis in the evolution of living nature and opened one of the ways (probably specifically terrestrial) for the formation of free oxygen.

By the end of the Archean (2.8-3 billion years ago), the first colonial algae appeared, the fossilized remains of which were found in Australia, Africa, etc.

The most important stage in the development of life on Earth is closely related to changes in the concentration of oxygen in the atmosphere and the formation of the ozone screen. Thanks to the vital activity of blue-greens, the content of free oxygen in the atmosphere has increased significantly. The accumulation of oxygen led to the emergence of a primary ozone screen in the upper layers of the biosphere, which opened the horizons for prosperity.

PROTEROZOIC. Proterozoic is a huge stage in the historical development of the Earth. During this period, bacteria and algae reach exceptional prosperity, and with their participation the processes of sedimentation proceed intensively. As a result of the vital activity of iron bacteria in the Proterozoic, the largest iron ore deposits were formed.

At the turn of the Early and Middle Riphean, the dominance of prokaryotes was replaced by the flourishing of eukaryotes - green and golden algae. From unicellular eukaryotes, multicellular organisms with complex organization and specialization develop in a short time. The oldest representatives of multicellular animals are known from the late Riphean (700-600 million years ago).

Now we can say that 650 million years ago, the earth’s seas were inhabited by a variety of multicellular organisms: solitary and colonial polyps, jellyfish, flatworms, and even the ancestors of modern annelids, arthropods, mollusks and echinoderms. Some forms of fossil animals are now difficult to classify into known classes and types. Among plant organisms at that time, unicellular organisms predominated, but multicellular algae (green, brown, red) and fungi also appeared.

PALEOZOIC. By the beginning of the Paleozoic era, life had passed perhaps the most important and difficult part of its journey. Four kingdoms of living nature were formed: prokaryotes, or shotguns, mushrooms, green plants, animals.

The ancestors of the kingdom of green plants were unicellular green algae, common in the seas of the Proterozoic. Along with floating forms, those attached to the bottom also appeared among the bottom. A fixed lifestyle required the dismemberment of the body into parts. But the acquisition of multicellularity, the division of a multicellular body into parts that perform different functions, turned out to be more promising.

The emergence of such an important aromorphosis as the sexual process was of decisive importance for further evolution.

How and when did the division of the living world into plants and animals occur? Is their root the same? Disputes among scientists around this issue do not subside even today. Perhaps the first animals descended from the common stem of all eukaryotes or from single-celled green algae.

CAMBRIAN– flowering of skeletal invertebrates. During this period, another period of mountain building and redistribution of land and sea areas took place.

The Cambrian climate was temperate, the continents unchanged. Only bacteria and blue-greens still lived on land. The seas were dominated by green and brown algae attached to the bottom; Diatoms, golden algae, and euglena algae swam in the water columns.

As a result of the increased washout of salts from land, marine animals were able to absorb large quantities of mineral salts. And this, in turn, opened up wide ways for them to build a rigid skeleton.

The most widespread arthropods - trilobites, which are similar in appearance to modern crustaceans - wood lice, have reached the widest distribution.

Very characteristic of the Cambrian is a peculiar type of multicellular animals - archaeocyaths, which became extinct towards the end of the period. At that time, there were also a variety of sponges, corals, brachiopods, and mollusks. Sea urchins appeared later.

ORDOVIK. In the Ordovician seas, green, brown and red algae and numerous trilobites were diversely represented. In the Ordovician, the first cephalopods, relatives of modern octopuses and squids, appeared, and brachiopods and gastropods spread. There was an intensive process of reef formation by four-rayed corals and tabulates. Graptolites are widespread - hemichordates, combining the characteristics of invertebrates and vertebrates, reminiscent of modern lancelets.

In the Ordovician, spore-bearing plants appeared - psilophytes, growing along the banks of fresh water bodies.

SILUR. The warm shallow seas of the Ordovician were replaced by large areas of land, which led to a dry climate.

In the Silurian seas, graptolites lived out their lives, trilobites fell into decline, but cephalopods reached exceptional prosperity. Corals gradually replaced archaeocyaths.

In the Silurian, peculiar arthropods developed - giant crustacean scorpions, reaching up to 2 m in length. By the end of the Paleozoic, the entire group of crustacean scorpions almost became extinct. They resembled the modern horseshoe crab.

A particularly noteworthy event of this period was the appearance and spread of the first representatives of vertebrates - armored “fish”. These “fish” only resembled real fish in shape, but belonged to a different class of vertebrates - jawless or cyclostomes. They could not swim for long and mostly lay at the bottom of bays and lagoons. Due to their sedentary lifestyle, they were unable to develop further. Among the modern representatives of cyclostomes, lampreys and hagfishes are known.

A characteristic feature of the Silurian period is the intensive development of land plants.

One of the first terrestrial, or rather amphibian, plants were psilophytes, which trace their ancestry to green algae. In reservoirs, algae adsorb water and substances dissolved in it over the entire surface of the body, which is why they do not have roots, and body outgrowths resembling roots serve only as attachment organs. Due to the need to conduct water from the roots to the leaves, a vascular system arises.

The emergence of plants onto land is one of the greatest moments of Evolution. It was prepared by the previous evolution of the organic and inorganic world.

DEVONIAN. Devonian is the period of fishes. The Devonian climate was more sharply continental; icing occurred in the mountainous regions of South Africa. In warmer areas, the climate changed towards greater drying, and desert and semi-desert areas appeared.

In the Devonian seas, fish flourished. Among them were cartilaginous fish, and fish with a bony skeleton appeared. Based on the structure of their fins, bony fish are divided into ray-finned and lobe-finned. Until recently, it was believed that lobe-finned animals became extinct at the end of the Paleozoic. But in 1938, a fishing trawler delivered such a fish to the East London Museum and it was named coelacanth.

At the end of the Paleozoic, the most significant stage in the development of life was the conquest of land by plants and animals. This was facilitated by the reduction of sea basins and the rise of land.

Typical spore plants evolved from psilophytes: mosses, horsetails, and pteridophytes. The first forests appeared on the earth's surface.

By the beginning of the Carboniferous, noticeable warming and humidification occurred. In the vast valleys and tropical forests, in continuous summer conditions, everything grew rapidly upward. Evolution has opened a new way - propagation by seeds. Therefore, gymnosperms picked up the evolutionary baton, and spore plants remained a side branch of evolution and faded into the background.

The emergence of vertebrates onto land occurred back in the Late Devonian period, after the land conquerors – the psilophytes. At this time, the air had already been mastered by insects, and the descendants of lobe-finned fish began to spread across the earth. The new method of movement allowed them to move away from the water for some time. This led to the emergence of creatures with a new way of life - amphibians. Their most ancient representatives - ichthyoschegi - were discovered in Greenland in Devonian sedimentary rocks.

The heyday of ancient amphibians dates back to the Carboniferous. It was during this period that stegocephals developed widely. They lived only in the coastal part of the land and could not conquer inland massifs located far from bodies of water.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The Paleozoic era is conventionally divided into 6 periods.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Geological eras of the Earth, or geochronological scale:

And now about everything in more detail:

Designations:
Eras;
Periods;
Epochs.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Quaternary period (1 million – our time);

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

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

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

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

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

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

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

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

, And You can read it in the same section.

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

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

One of the important tasks 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, which led 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 how the primary crust of the Earth was probably formed, which, however, was not preserved on its modern surface, with the exception of relatively small fragments in the “younger” continental-type crust.

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

Principles of periodization of the geological history of the Earth

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

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

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

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

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

In 1881, at the II International Geological Congress in Bologna (Italy), the main divisions of combined stratigraphic (for separating layered sedimentary rocks) and geochronological scales were approved. According to this scale, the history of the Earth was divided into four eras in accordance with the stages of development of the organic world: 1) Archean, or Archeozoic - the era of ancient life; 2) Paleozoic - the era of ancient life; 3) Mesozoic - 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 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 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 formed a single mass - the supercontinent Megagaea (big earth), which on the other side of the globe was opposed by an ocean - the predecessor of the modern Pacific Ocean - Megathalassa (big sea). This ocean was less deep than modern oceans, because the growth of the volume of the hydrosphere due to degassing of the mantle in the process of volcanic activity continues throughout the subsequent history of the Earth, although more slowly. It is possible that the prototype of Megathalassa appeared even earlier, at the end of the Archean.

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

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

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

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

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

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

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

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

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

QUESTIONS FOR SELF-CONTROL

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

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

What are the main physical parameters 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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Geochronological table- this is one way of representing the stages of development of planet Earth, in particular life on it. The table records eras, which are divided into periods, their age and duration are indicated, and the main aromorphoses of flora and fauna are described.

Often in geochronological tables, earlier, i.e., older, eras are recorded at the bottom, and later, i.e., younger, eras are recorded at the top. Below is data on the development of life on Earth in natural chronological order: from old to new. The tabular form has been omitted for convenience.

Archean era

It began approximately 3500 million (3.5 billion) years ago. Lasted about 1000 million years (1 billion).

In the Archean era, the first signs of life on Earth appeared - single-celled organisms.

According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean there was the Catarchean era, when there was no life yet.

Proterozoic era

It began approximately 2700 million (2.7 billion) years ago. Lasted for more than 2 billion years.

Proterozoic - the era of early life. Rare and scarce organic remains are found in the layers belonging to this era. However, they belong to all types of invertebrate animals. Also, the first chordates most likely appear - skullless.

Palaeozoic

It began about 570 million years ago and lasted more than 300 million years.

Paleozoic - ancient life. Starting with it, the process of evolution is better studied, since the remains of organisms from higher geological layers are more accessible. Hence, it is customary to examine each era in detail, noting changes in the organic world for each period (although both the Archean and the Proterozoic have their own periods).

Cambrian period (Cambrian)

Lasted about 70 million years. Marine invertebrates and algae thrive. Many new groups of organisms appear - the so-called Cambrian explosion occurs.

Ordovician period (Ordovician)

Lasted 60 million years. The heyday of trilobites and crustaceans. The first vascular plants appear.

Silurian (30 Ma)

• Coral blossom.
• The appearance of scutes - jawless vertebrates.
• The appearance of psilophyte plants coming onto land.

Devonian (60 Ma)

• The flourishing of the coryptaceae.
• Appearance of lobe-finned fishes and stegocephali.
• Distribution of higher spores on land.

Carboniferous period

Lasted about 70 million years.

• The rise of amphibians.
• The appearance of the first reptiles.
• The appearance of flying forms of arthropods.
• Decline in trilobite numbers.
• Fern blossoming.
• The appearance of seed ferns.

Perm (55 million)

• Distribution of reptiles, emergence of wild-toothed lizards.
• Extinction of trilobites.
• Disappearance of coal forests.
• Distribution of gymnosperms.

Mesozoic era

The era of middle life. It began 230 million years ago and lasted about 160 million years.

Triassic

Duration - 35 million years. The flourishing of reptiles, the appearance of the first mammals and true bony fish.

Jurassic period

Lasted about 60 million years.

• Dominance of reptiles and gymnosperms.
• The appearance of Archeopteryx.
• There are many cephalopods in the seas.

Cretaceous period (70 million years)

• The appearance of higher mammals and true birds.
• Wide distribution of bony fish.
• Reduction of ferns and gymnosperms.
• The emergence of angiosperms.

Cenozoic era

An era of new life. It began 67 million years ago and lasts the same amount.

Paleogene

Lasted about 40 million years.

• The appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
• Rapid flourishing of insects.
• The extinction of large reptiles continues.
• Entire groups of cephalopods are disappearing.
• Dominance of angiosperms.

Neogene (about 23.5 million years)

Dominance of mammals and birds. The first representatives of the genus Homo appeared.

Anthropocene (1.5 Ma)

The emergence of the species Homo Sapiens. The animal and plant world takes on a modern appearance.