Precambrian period. Precambrian structure and composition

Precambrian, the Precambrian period or cryptose is the first part of the geological history of the Earth. Precambria is total name of three eons Stories of the Earth - (4.6-4.0 billion years ago), (4.0 to 2.5 billion years ago) and (2.5 billion to 541 million years ago). Thus, the Precambrian covers most of the history of the Earth (4.6 billion years ago - 541 million years ago, or 90% of the entire geological history of the Earth). Precambrion, consisting of three eonov, precedes the last Eon - - which continues today.

Precambria is the period of the formation of the Earth, the period of the initial development of the earth's crust, the formation of the atmosphere and the first period of life development. Scientists have distributed periods - Precambria and Plyeroza - in such a way that the Precambrian period ends with the beginning of the era and the Cambrian period. The Cambrian period is known for such an amazing phenomenon as "" when there appeared the mass of living organisms on the planet. A huge variety of developed forms of living organisms in the Cambrian period still causes hot contrasts of scientists, but it will be possible to learn about it in one of the following articles.

Meaning This distribution of geological periods in the history of the Earth lies in the fact that Precambria or Cryptose (cryptose - from the ancient Greek "secretive life") is the period of the formation of the Earth, when life just started to develop, and he ends at that time, which is known to all paleontologists As the beginning of the rich deposits of fossil living organisms. From that moment on, it begins plywood (from ancient Greek - obvious life).

Initially, the Precambrian period or Cryptose was called Azoic era, that is, era without life, the first era of the history of the planet, when there was no life. However, subsequent studies made it possible to find out that the azoic era was settled with alive organisms, although not to such an extent, as in the subsequent plywood. The first life appeared at the very beginning of Archey, 3.7 billion years ago, after which the Azoic period became inappropriate, and he had new names - Precambria (that is, a period to Cambrian or Cambrian Blowjobs) or Cryptose (secretive life) .

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Despite the fact that very few times are known about those distant times, many of the amazing creatures that inhabited the land in that era come to life in the skillful hands of paleontologists and biologists.

From creating any skeletons, of course, not preserved. Mostly because, in fact, the skeletons did not have any animals then. In Kembria, however, the bone shell and the routine of chords, they still found, but for the prescription, it is not necessary to count on their safety. All information about the animals of the Venndsky period (Precambria, or, as elsewhere, ediacary, who has been 635 to 541 ± 1 million years ago) and Kebria (which began approximately 541.0 ± 1 million years ago and ended 485.4 ± 1 , 9 million years ago) scientists are obtained by imprints.

One of the main sources of these prints today is the shale of Burgez, located in Canada.

This mild animal of the Vennd period had a one-piece head in the shape of a crescent, similar to the trilobite shield, as well as a long body, which consisted of the same segments and resembles the body of multi-singing worms.

Another Animal Ediakaria, quite strongly resembling the aforementioned Spriggin. A characteristic feature of many vendan organisms is that the segments of their bodies are shifted to each other (Dickinsonia, Charnia, etc.) contrary to all the laws of bilateral symmetry (symmetry of the mirror reflection, in which the object has one plane of symmetry, relative to which two half of the mirror symmetrical; bilateral symmetry includes human bodies and most modern animals - NS). This fact puts scientists in a dead end, since it was previously believed that the ancestors of the ringed worms are VenDan animals. Today, this idea is questioned, which is very puzzling researchers trying to trace the origin of some species from others.

Another "resident" of the Vendian period - Dickinsonia

Ediakar animals - Irania (shown in blue), below - three-beam albumares

But this creature of the Cambrian period was introduced by paleontologists so amazing that they seemed to them as if they see hallucinations. Hence the name. After all, if you judge the preserved prints of this animal, it is logical to suggest that instead of the legs he had spikes (and two or three in one segment), and a number of some soft processes were located on the back! It is hardly possible from the point of view of biological science. Fortunately, later, clearer imprints were found, on which it was clear that the hallucigious was simply turned upside down, and the second row of its soft legs did not affect the imprint. Thus, hallucigations looked like this:

Draw-like animal Cambrian. It may be fed with sponges, since her remains often find along with the remains of sponges.

Representative of a new generation of multicellular organisms, the genus of fossil soft-sword scaly animals. It is assumed that Vivaksia lived from the end of Lower Cambrian to the Middle Cambrian.

Primitive chord animals with a length of only about 5 cm, possessed, perhaps, one of the first in the history of spine. For millions of years, this simple structure will turn into a spine, without which we could neither stand nor walk. By the way, the appearance of a skeleton as such as such, as well as more advanced eyes - one of the most important factors characterizing the Cambrian explosion.

Another major representative of Cambrian and subsequent geological eras. This is a extinct class of marine arthropods. Perhaps one of the most numerous and most lively species of creatures ever lived on Earth. The trilobites were not very cute and resembled modern wets, only much harder and more - the length of their body could reach 90 cm. To date, more than 10 thousand fossil types of trilobite class are known.

From the ancient Greek class of dinocarid (DinoCarida), to which an anomalocaris belongs, is translated as "unusual" or "terrible" shrimp. " Probably the most amazing animal of the Cambrian seas. Anomalocaris, predator of the kind of fossil arthropods, found not immediately - first discovered his parts and long bred hands over such an amazing animal. Thus, the imprint of the tooth-out mouth anomalocaris was counted by a strange jellyfish with a hole in the middle. The limbs that he had enough sacrifice - shrimp. The picture cleared when a full animal imprint was found.

Anomalocarisses were inhabited in the seas, floated with flexible side blades. This is one of the largest organisms known in Cambrian sediments. The length of their body could reach 60 cm, and sometimes 2 m.

No less amazing creatures similar to anomalocaris. Like anomalocaris, all of them are representatives of the extinct class of dinocarid. But instead of grabbing processes, "shrimps" in the opacity - folding trumps and five eyes.

Marella is at all like a monster from horror films, and Hurdia Victoria was among the largest predators of the Cambrian period, reaching a length of 20 cm. The mouth of these creatures was framed 32 plates carrying two to three teeth.

In general, as already I wrote somewhere, the Precambrian would have a great fans of beer because of the abundance of snacks to Oyom. The joke as always understood not all and began to demand in the bars of fresh trilobites

From the emergence of land to 570 million years ago.
The Epoch of Precambrian continued from the moment of the formation of the Earth until the first multicellular organisms appear about 570 million years ago. The age of the oldest of the rocks known to us is only 3.9 billion years, so we know about the youth of our planet is negligible. Moreover, even these rock breeds have undergone a billions of years such large transformations that few can tell us about.
About 2.5 billion years ago, the whole earthly land was, apparently, merged into one huge supermaster, subsequently glued to several.
By the end of the era of Precambrian, the mainland again merged, forming a new supermaster. All these perturbations on land and the sea were accompanied by ambitious climatic changes. During the Precambria, the world survived at least three glacial periods. The most ancient began about 2.3 billion years ago. The most ambitious glaciation in the history of our planet occurred between 1 billion and 600 million years ago.
The early atmosphere of the Earth did not contain oxygen. It consisted mainly of methane and ammonia gases, fewer hydrogen sulfide, water vapor, nitrogen and hydrogen, as well as oxide and carbon dioxide. However, with the emergence of life on Earth, the picture has changed dramatically.

First cells. Methane and other gases contained in the primitive atmosphere of the Earth were dissolved in the water of the seas, lakes and puddles, forming a complex chemical "broth" (1). Laboratory experiments have shown that under the influence of lightning discharge in such a "broth", chemical reactions begin to occur and more complex chemical compounds are formed, very similar to those found in living cells (2). Ultimately, some of the organic compounds acquired the ability to self-reproducing, that is, they began to create copies of themselves (3). In the same "broth" contained fat balls (4). When the wind mixed the "broth" strongly, some complex compounds could fall inside these fat balls (5) and stay there "locked." Over time, these hybrid structures evolved into living cells surrounded by a fatty shell.
Matter life.

All living creatures contain a certain set of special chemical compounds.
The cell mainly consists of proteins or from substances synthesized by them. All proteins encountered in living matter are formed by the threads of special chemicals - amino acids. Cells also contain another chemical substance - ATP used to accumulate energy.
The program for creating new cells - and even new animals or plants - exists in the form of a special chemical code contained in a long molecule called DNA. Each variety of living organisms has its own DNA type. All these substances are proteins, ATP and DNA - contain carbon, that is, organic compounds. But how did the first organic substances arose?

Life puts experiments

Gases formed the early atmosphere of the Earth were gradually soluble in the World Ocean, and there was a kind of "warm soup" from chemical compounds. Since the atmosphere did not have oxygen, there was no ozone layer (ozone - a type of oxygen), which could be protected ground surface From malicious ultraviolet solar radiation.
In the 20s XX century Russian scientist Alexander Oparin and English scientist John Haldane nominated a hypothesis, according to which many millions of years are radiation,
Together with the discharges of lightning, created in the chemical "broth" more and more complex chemical compounds, until one organic connection appeared - DNA capable of reproducing itself.
In the 50s. XX century American Chemist Wengy Miller decided to check this hypothesis. He mixed methane and ammonia above the surface of warm water and missed the electric current through them, creating something like lightning. Miller repeated this experiment repeatedly, changing the composition of the gas mixture and the temperature regime. In several cases, he found that in just 24 hours, about half of the carbon contained in methane turned into organic compounds Amino acid type. It means that it can be concluded that with sufficient time and the corresponding composition of the gas mixture could also form more complex chemical compounds, perhaps even those of them, which are part of the DNA.

First living cells

Chemical "broth" in the primitive ocean became all thicker, and all new and new connections were formed. Some of them have formed thin solid films on the surface of the water - like the film from the oil ranging into the sea. Water was stirred, for example, during a storm, and the film burst into separate spherical formations, similar to oil balls. Inside them were separate chemical compounds that began to resemble the real living cells. It was worth only the DNA molecules to form in the "broth" and find themselves together with other substances inside such a shell, as it laid the beginning of life on Earth.
The first cells largely resembled modern bacteria. They produced the necessary energy, splitting inorganic compounds. Cells could remove carbon from methane, as well as from oxide and carbon dioxide dissolved in water.
From hydrogen sulfide and other compounds containing its compounds, they removed hydrogen. All these cell elements were used to reproduce new live matter. Such bacteria in our time are found around hot mineral springs and existing volcanoes.

Primitive forms of bacteria and cyanines (syneselen algae) and to this day in abundance are found in hot mineral springs. Some of them use mineral substances from these sources as "raw materials" for photosynthesis.
Scientists believe that life could be born in a similar environment. At the bottom of the picture, if you look more attentive, you can distinguish between two people on the path beside the source.
Scrolling the energy of the sun.

The next most important stage in the evolutionary process is the taming of solar energy by living matter. Instead of removing energy from inorganic compounds, the cells began to use directly the energy of the sun's rays.
This marked the beginning of photosynthesis, a special process, during which the plants synthesize nutrients using the energy of sunlight. L Instead of obtaining the necessary cells of hydrogen from such substances such as hydrogen sulfide, they learned to extract it from a much more common substance - water.

Photosyntheses: a huge jump of evolution

Plants, algae and some types of bacteria "capture" sunlight with the help of painted chemical compounds contained in cells - so-called pigments. These light energy are used to synthesize all organic compounds needed by it for growth and reproduction. Such a process is called photosynthesis, which means "creation with light". To create complex compounds from simple chemicals, for example, sucrose or proteins encountered in living cells, you need to spend a certain amount of energy. In many ways, it resembles the construction of the wall: To raise bricks on the top of the wall and fasten them on a put place, you need energy. With photosynthesis, this energy comes from sunlight. Carbon dioxide (containing carbon and oxygen) and water (consisting of hydrogen and oxygen) give carbon, oxygen and hydrogen. Of these, sucrose and other organic compounds produced during photosynthesis are synthesized. In this case, not all oxygen consumes it is thrown into the atmosphere.
To capture the sun's rays, these new photosynthetic cells produced pigments - painted substances capable of absorbing light. Until that time, the life of Pa Earth was dim and colorless. Now she played multi-tie new colors. From now on, living organisms have ceased to be tied to places with particularly energy-intensive substances: water and sunlight turned out to be much more accessible sources of energy.
New photosynthes were inhabited mainly in mineral springs and warm coastal waters of the seas, where it was finely enough to reach the sunlight, and at the same time it is quite deep enough to protect them from the destructive effects of ultraviolet radiation. Some of the cells continued to highlight hydrogen from hydrogen sulfide; Their descendants still meet the hot mineral springs.

Live stromatolites in Bay Shark, Australia. Since photosynthesis occurs in stromatolites, they are removed from water dissolved carbon dioxide. In this case, calcium carbonate (lime) is distinguished from the solution. The adhesive mucus produced by stromatolites, captures tiny particles of lime, and as a result, limestone layers are formed.
An image of fossil stromatolite in the context, which is clearly visible layers of limestone and cyanobacteria.
The era of Stromatolites.

Some of the earliest photosynthetic organisms that have come down to us in the fossil form are stromatolites (see also with. 34). These strange structures seem at first glance consisting of many limestone rings separated by thin conical layers. In fact, they were formed primitive organisms, similar to the simplest cyanocteria, which are sometimes called blue-green algae. Stromatolites were distinguished by an incredible variety of forms and sizes. Some were round, like potatoes, other cone-shaped, third - high and thin or even branched.
The petrified stromatolites are found worldwide. In many places, they form huge reefs, often rising from the seabed for hundreds of meters through the thickness of transparent water, like modern coral reefs in the tropics. The oldest fossil stromatolites were discovered in Western Australia, in rock rocks of 2.8 billion years. However, unidentified structures, which, according to scientists, could also be petrified stromatolites, are even in rocks by age at least 3.5 billion years. Living stromatolites live on Earth and today. They, like their distant ancestors, prefer warm shallow water. However, the current area of \u200b\u200bStromatolites is limited only to those places where few animals feed.

Red color sediments

Some of the most ancient fossos, including many stromatolites, are found in rocks, referred to as shale, which is uncharacteristic for sedimentary breeds of later eras. It has long put in a dead end of geologists, until they finally reached that the formation of such layers is associated with the vital activity of stromatolites. Gradually, the oxygen concentration in the oceans increased, and it began to enter into chemical reactions with dissolved and water with iron. Formed
Kon "with its own shell - the so-called organelles. In each compartment there was a special internal environment, therefore various processes occurred in different parts of the cell. Now the chemical reactions in cells began to flow much more efficiently. The DNA substance containing the genetic code has arranged in special Structures - chromosomes. Scientists believe that these new cells were formed when aerobic cells began to penetrate inside other cells - it is possible to protect against new "predatory" cells. At the same time, new cells shared with each other and generated by chemical compounds.
Compounds of iron and oxygen are so-called iron oxides. They could not be dissolved in water and settled to the bottom along with other precipitation.
Approximately 2.2 billion years ago, sedimentary breeds of a new type were also launched on land - the so-called red-colored sediments. These breeds contained a large number of Iron oxides, which gave them a reddish shade of rust color. "It means that by that time oxygen appeared in the atmosphere. All iron in the ocean has already been connected, and excess oxygen fell into the atmosphere in the form of gas.

Poisoned oxygen

Throughout the Precambrian, the concentration of oxygen in the atmosphere of the Earth was constantly increased. However, many living organisms of that time it did not bring anything good. For them, it was equivalent to grandiose atmospheric pollution. After all, the first living organisms arose in an oxygen-free medium, and the oxygen turned out to be a deadly poison for them. Many species disappeared from the face of the earth - it was the first great extinction in its history. Truly disappointing paths of evolution: today we are not thoughts of life without oxygen, and for the first living organisms oxygen in the atmosphere was mortal.
Ultimately, evolution made a cell that could not just
To live in an oxygen environment, but also to turn her for good. After all, some compounds formed during photosynthesis may be cleaved with oxygen, and the energy allocated can be used to create a number of new connections. In most living cells and now the respiratory process proceeds. Scientists call it an aerobic breathing type ("aerobic" means "using air"). During this process, energy is released much more than with any other biorescape processes occurring without oxygen. Some "breathable" cells even acquired the ability to absorb other cells using them as food.

The very first cells, the so-called prokaryotes (left), were extremely primitive. All chemicals contained in them, including DNA with a genetic code, were mixed and scattered throughout the cell. In later - eukaryotic cells (right) there were small internal compartments with their own shell. They contained chemicals for certain reactions, and in each of them it was the medium that is necessary for the fastest flow of this reaction. DNA was concentrated in chromosomes located inside the cell core surrounded by a nuclear sheath. The kernel managed the entire vital activity of the cell.
Preparing the scene for evolution.

Oxygen in the atmosphere accumulated, and there began to form an ozone layer, which absorbed the malicious ultraviolet radiation of the Sun. Now life was able to move closer to the surface of the oceans and even penetrate the wet coastal areas of sushi. Cianobak Terii also became more complicated. They began to group in Komny and subtle threads. Nevertheless, new aerobic cells breathing oxygen gradually took over.

Variability - life catalyst

More importantly, new cells began to multiply in a completely different way. Instead of simply to share in half and form two other cells - accurate copies of the previous one, these new cells began to do something strange. Two cells merged into one, exchanged part of their DNA, and then again shared for two or more new cells. This is called sexual reproduction. New cells from now on possess mixed DNA from both their parents. Sexual reproduction led to a sharp increase in variability among cells, which, in turn, gave a powerful impetus to the evolutionary process.

First great extinction

Late Precambrian was marked by grandiose natural cataclysms. They were accompanied by numerous eruptions of volcanoes, earthquakes and plotting processes. A huge amount of volcanic ash, thrown into the atmosphere, led to climate cooling; Huge arrays of sushi put out the poles, and giant glacial coverings were mounted around the globe.
During this period, very many types of ancient organisms have died out. In the end, the ice began to melt, the ocean level gradually increased, and the water flooded the coastal areas of the mainland. For creatures that lived in shallow water, new, not yet occupied land with unlimited possibilities of conducting a specialized lifestyle. By this time, the surface of the Earth reached a much less dangerous ultraviolet radiation of the Sun than before, since it could not overcome the condensed ozone layer. In addition, the oxygen in the atmosphere was now more, which quite satisfied the new generation of living organisms.

Today, the great many of a variety of single-cell organisms live in the upper layers of the World Ocean. Many of them must be very similar to those inhabited the seas of the Precambrian era. At the top: in front of you microscopic glassy skeletons of radiolearium - single-cell animals with long subtle processes covered with adhesive mucus, with which they caught the extraction of crumbling organisms. Below: lime multi-chamber foraminifera shells are important guidelines. These shells form the basis of certain types of limestone. Like radooles, unicellular foraminifera had long adhesive processes for fishing.
Mystery of multicellular.

Nobody really knows how the first multicellular animals arose. Perhaps at some point, the separated cells stopped completely separated from each other. Or, on the contrary, various cells began to unite and self-organized. At first glance, it seems incredible, but do not hurry with conclusions. In 1907, the biologist X. J. Wilson held a number of experiments with sponges. He cut a red sponge into small pieces and began to skip them through a special installation in order to separate the cells from each other - until finally got a red sediment in a decanter with water. To a considerable surprise, in a matter of hours, the cells were again grouped into a single whole. Then they gradually began to be self-organized into a new sponge, forming cameras, channels and branched tubes. A week later, the sponge was like new. It is possible that the first multicellular animals were formed.
Now there are also such strange creatures like mucus, or mixomy-you. They look like brightly colored lumps of mucus, creeping on the ground or on the crust of trees. One of the varieties of mucus, cellular mucus, is spent most of their lives in the form of individual cells, smoking in the soil, where they feed the bacteria. But when the food reserve is running out, each cell produces a special substance that attracts other cells of the mucus. Millions of such cells are assembled together and form a huge cellular mass, which is very smachy for a multicellular organism. This mass moves and reacts to light and chemicals, like a single animal. Ultimately, the mucus appears in the form of a fruiting body, in many respects similar to the sporangies of any mushroom. It has a high leg with a protective outer shell, and on top there is a bag with disputes.

Mixed in Ile

These early soft animals had little chance to preserve in fossil form. However, they left their traces in rock or, more precisely, prints. Snacks, of which the soft-breeds mined food, prints of bodies and celebrated in the thickening of il, where they rested, discovered in rocks whose age is 700 million and more. However, in sediments, up to those whose age is 640 million, such traces come across extremely rarely. By the end, the glaciation of the late Precambrian was just approached and the conditions for a new grand evolution explosion were formed.

One creature or many organisms? In response to the chemical "signal" millions of album-shaped cells are collected together, forming a moving film, which ultimately distinguishes dispute capsules on long legs, in many respects resembling the simplest mushrooms.
Ediacar animals.

In the remote part of South Australia, in the Ediacarian mountains, there are ancient shallow and coastal sedimentary rocks, which is 640 million years old. A lot of mineral remains of the Pokurgrysky era are preserved here. In these breeds, at least 30 different types of multicellular organisms were found; It should be noted that similar accumulations of fossils are found in rocks of the same age in many places around the globe.
Ediacar animals lived predominantly on the seabed. They were fed into the layer of organic matter (Detritis), which covered the bottom Il, formed by the remains of many single-cell organisms, which inhabited the thickness of the water over them. Flat and collected worms floated over the very bottom or crawled among precipitation. It was nowhere to hurry, because predators (animals that feed on other animals) were very small here.
Sea feathers rose from the seabed, like some perverse flowers, carefully filtered by water in search of food. Tubular worms were lying among bottom sediments, shehell her tentacles in a dampite water. Primitive Icharkin, Raigue of modern marine stars and sea hero, all his life was performed in a thick layer of Slah. There were a lot of large flat animals in the form of pancake; These simply similar to jellyfish creation also, apparently, dwell on or end. And over them in the sea water, real jellyfish was slowly floated.

Future precursors

In Ediacarchic sediments there are numerous petrified prints of soft animals that have passed once along the seabed. In some places in Ile, pair V-shaped marks are captured, similar to the scratches left by pair of tiny legs. Perhaps traces of primitive arthropods, or arthropods, - distant ancestors of fossil trilobites, as well as modern insects - spiders and scorpions. True, the solid remains of these animals have not yet been discovered: apparently, they have not yet acquired a solid shell.

All Ediacar animals were mild. There were a lot of varieties of jellyfish (1). Dixony (2) and Spriggins (3) were flat dwarf creatures. Spriggin had many tiny swimming plates along the sides, like modern sea worms. Perhaps this is an ancestor of trilobites. Harnyodisk (4), rank "(5) and Pterydinium, leaf-shaped marine feathers were the colonies of tiny animals, similar to hydr, which were filtered out of the water of food particles. But the tribrahidi (7) is a complete riddle for us. He had a Y-shaped central Mouth with bristle-shaped processes. Perhaps he is a ancestor of modern osklinodi.

Precambrian

Docke.mbry, The oldest stratum of the earth's crust and time corresponding to their formation and constituting about 6/7 of the geological history of the Earth. The geological history of D. remained unknown for a long time, despite the fact that various traces of life were discovered in the rocks of D. long ago. The paleontological method that has justified itself in the dismemberment of Puerozoic (Locabyrian) formations, here was considered not applicable. For individual regions, a purely local dismemberment of D. cuts was given, because The method of their interregional comparison was absent. Only in the 30s. 20 V. In the study of stratigraphy and geochronology D. The radiometric methods began to be used (see Geochronology), and attempts to compare the sedimentary thickness of D. on stromatolites (the construction of ancient algae) were made. Duration D., according to modern data, is determined on the occurrence of the most oldest geological formations known to us with about 3500 million years old before the beginning of Kebria (about 570 million years ago). T about., Duration D. amounted to more than 2,900 million years. An earlier period of the history of the Earth (about 1 billion years) is not yet available to geological study.

Dismemberment of Precambria. In the 2nd half of the 19th century Based on the general historical and geological data, the degrees of metamorphism of rocks and others. Signs in North America were proposed to dismember D. on Archaei, or archeoos (allocated by J. Dana in 1872), and proteodes (installed by Emmons in 1888). The border between them, according to modern ideas, coincides with the large era of folding and granitization, which had a place of 2500-2700 million years ago. In the USSR, the protein is usually divided into the lower, medium and top (see table). The upper protester is often isolated under the name "Rifey" ("Inframbembry", "Blue") and divided according to the composition of organic residues for 4 parts. The upper subdivision of the Rifey, which was previously converted to the so-called transitional layers from the Proterezhoy to Paleozoa, is isolated under the name "Vend" ("Yudomius", "Eokembry", etc.).

DCCOMBRY units			End of sub-separations (million years)
Proterozoa

B The initial period of studying of the Precambrian formations instead of the term "D." A number of others were used, now found only in the works of foreign geologists. These include, for example, the protozoa sedzhvik (1838), the type of which is strongly metamorphized rocks of the Schotland Scottish Nagrain, Wales, etc. The sharp difference between the rhymes from more ancient formations of D. (relatively weak metamorphism of the foundation of its breeds and the possibility of paleontological dating of accompanying thickness) He led to the fact that the division of D. on the lower (early) D., covering the thickness of the rocks of the Archey, the Lower and Middle Proterezhoy, and the Upper (Late) D., corresponding to the rife (from 1600 million years before the beginning of Kebria) .

General characteristics. Delaimal D. are common at all continents within ancient platforms: Eastern European, Siberian (along with its ancient folded framing - a ridge, a Patoman Naggorn, the northeastern part of East Sayan and the Yenisei Kryazh), Sino-Korean, South China and Indian, as well as the North American, South American, African, Australian and Antarctic. In addition, the Precambrian Education is based on the nuclei of raising, including the median arrays in the oldest folded zones framing the ancient platforms - Baikal, Caledonian, Gersinskaya (Varisskaya) and Alpine.

The geological formations of the early D., largely metamorphosed, are found in the foundation of ancient platforms and go to the surface in the field of their crystal shields - the Baltic, Alandan, Canadian, etc. Sometimes within the ancient cores of consolidation (in North America, South Africa, etc.) Weakly changed sedimentary and volcanogenic breeds related to radiological data, to early D. At the same time, the ancient platforms include extensive areas (the Grenville belt of North America, the Mozambique belt of Africa, etc.), containing the deposits of the early D., which were exposed to the thermal effect In the later epochs of the Precambrian folds. Often developed in these zones of gneisses with "rejuvenated" values \u200b\u200bof absolute age without sufficient grounds belong to Late D.

Education of the Upper D. Most often they are based on the lower part of the sedimentary cover of ancient platforms and are presented by relatively poorly modified rocks in which they often persist glauconite et al. Minerals that are destroyed even with weak metamorphism.

Rannedokembry Education is consisting of gneisov, migmatites, a variety of crystalline slates, amphibolites, less often jespilles, quartzits and marbles. They are found in powerful strata collected in complex folds and broken by large intrusions of various composition and age (granites, grandiors, gabbro, etc.). These stratas indicate mobile (geosynclinal) conditions of development that prevailed on all the continents in the early D. at the end of the early D. appear weakly allocated and weakly metamorphized formations of platform type, broken by intrusions of the main and granite rocks. The formation of late D. is closer to Paleozoic and are represented by powerful strata of quartz sandstones and quartzites, clay shale and phyllitis, various volcanogenic formations, stromatolithic dolomites and limestones, less often the stalls close to flush. At the very end of D. The thickness of the breeds appear similar to melassami.

Based on breaks and disaglements in the simulation of rocks and sharp changes to the degree of their metamorphism in D., a number of epochs of increased texton-magmatic activity were established (see. Precambrian epochs of folds).

Flora and fauna. In the Precambrian sediments, there is no skeletal fauna, which serves as the basis for building a stratigraphic scale of Plyonozoic, nevertheless a variety of traces of organic life here are quite a lot. These include productivity products of blue-green algae (stromatolites) and bacteria (oncolites). The age of including their ancient deposits, by radiological data, is determined by more than 2500 million years. Stromatolites and oncolites are successfully used to compare sedimentary thickness of the upper protein within individual regions and even for intercontinental correlation. In the siliceous rocks of the early D., peculiar nice algae, having good safety, at which it is possible to observe the details of the cellular structure of the body. In many stratigraphic levels, the smallest rounded calves (up to 50 m) of algae origin, previously accepted for disputes, are found in the Precambrian strata. They are known as "acritar", or "spherumorphid". These formations are noted in early D. sediments, but they are especially abundant in late D., where, based on their vertical distribution, there are attempts to correlate the cuts.

The animal world D. is much poorer than plant. Separate instructions for finding in the breeds of D. animal residues relate to objects that seem to have inorganic origin (Aticocania Walcott, Tefemar Kites Dons, Eozoon Dawson, Brooksalla Bassler) or are stromatolite leaching products (Carelozoon Metzger). Many fossils D. are not fully decrypted (UDokania Leites) or have no accurate binding (Xenusion Querswalde Pompecki). In the middle of the Rifee of the Turukhansky district of the Krasnoyarsk Territory, the oldest subelldites are known, which are compared with modern pursuit. The most rich and diverse animal world of Wanda, studied in detail on unique finds made in sandstones Pound Australia and the Nama South Africa series. Here are found forms close to modern marine feathers (Rangea, Gharnia), ancient Annelides (Spriggina), numerous meduzoid forms (Ediacaria, Beltanella, Protodipleurosonia) and forms of unclear systematic accessories (Parvancoria, Dickinsonia). Numerous medzoids were found and Venda Eastern European Platform. VENDIA Sokolovi Keller is encountered in Wenda with a clearly segmented torso, but not having bilateral symmetry characteristic of trilobites. All listed forms are devoid of solid skeletal parts, their prints can only be maintained in exceptional cases.

Precambria of the USSR. In the USSR sediments of the early D. are very widely distributed. Best of all, they are studied on the Baltic Shield and in Eastern Siberia. Rannedokembrybral education of the Baltic Shield are represented by the thickness of the rocks of the Archean and Lower and Medium-Proteorozoic age. The first include the Kola series of mica and saliva-pomegranate gneisses with ferrous (ore) quartzdes of the Kola Peninsula and Gneoiso-shale Belomorsk series of Karelia; Both series are difficult to deployed and are broken by intrusion of the oldest major rocks (amphibolites), grateiorities and granites. The age of Archean folded structures (Saamydes, Wholerid) is determined at 2500-2700 million years. The Lower Midfields of Proterozoic Age are represented by Karelian formations of Karelia, Kola Peninsula. Attentionally, Svetefennian formations of South Finland and Sweden are considered to be considered. Stabilization of the territory of the Baltic Shield began 1900-2000 million years ago at the belt Kellid and ended 1800-1900 million years ago in the belt Svetefennide. On the Ukrainian shield, the Archean formations include the Konkovshetsevski series of amphibolites, shale and ferrous quartzites, a series of deeply metamorphic gneisses wagging, Volyn, Dneprovia, and other areas and conjugate granitoids and charanoises. The lower and medium protein is most typically represented by the Saksagan metabasic series and the overlying iron ore, sandstone-shale Krivoy Rog series. Similar to them series are available on the Voronezh array. According to drilling in the foundation of the Russian Plate of Education of the Early D., do not differ from those of the Baltic shield.

In Siberia, the Lower Middokembry formations are developed in the Siberian platform (within the Anabar massif and the Alandanian shield), in its Western, South and South-Eastern Framing (from the Yenisei Grocery and Altai to the eastern end of the Range), as well as on Mallar Hingane, Khankai Massier, On the northern coast of the Sea of \u200b\u200bOkhotsk, in the Kolyma pool, in the Chukotka and Taimyr Peninsula.

The ancient formations of the Archean era in Siberia are represented by mica-pomegranate, cordyerite-sillimanite, pyroxen gneisses and shales, granulites and marbles, divided into several series, is largely difficult to compare each other. The lower and medium protein is represented by a variety of gneis (mica, amphibole, sillimanitis, etc.), part of marbles and quartzites (East Sayan, Yenisei Kryazh, etc.) and less metamorphized sand-aurolithic strata (Udokan Ridge, etc.).

The deposits of the Upper D., the foundation of the platform cover, are common in the Urals and Timan; They are opened by deep drilling bodies on the Russian plate, are naked in the natural yields along the shores of the Dniester and the White Sea. Especially fully, they are presented in the Southern Urals, where in the context of the late D. with a total capacity of 15 kM three large series are highlighted. The Ural section concludes a number of horizons with stromatolithol and glauconitic supports was taken by N. S. Shatsky for the type of Rifey Group. Within the Russian Plate, Ripha performs linearly elongated deficits ( avlacogens), and the sediments of the Venda are distributed on more extensive areas, the lining of Moscow synecliz and other depressions. They are mainly represented by sandstones and aleuroliths and contain TILILIT assaults deferred to the ancient glacier. In the Siberian Platform of the Late D. are represented at the bottom of quartz sandstones and quartzites, and above are powerful carbonate strata. In terms of the composition of Stromatolites, all the subdivisions of Reefy are scheduled. In the deflections, framing the Siberian platform, sweates folded by carbonate rocks alternate with the strata of sandstones and slates. In the top of the cut on the South and Western Framing of the Siberian Platform, larger-grade stals appear, sometimes red-color. Many researchers consider them as orogenic education, comparing later geological periods with Molessia.

In the folded systems of Central Asia, Kazakhstan, the Far East, the formation of D. is also known as the deposits of early Precambria and Rhypsic sediments folded by sedimentary and volcanogenic geosynclinal thicknesses, sometimes with the layers of stromatolite limestone, which determine the identity of the accommodating deposits to the middle and top rife and Wanda . In some places from under Riphean Tasci (Kyrgyz Ridge Tien Shan, Ridge Ulutau in Kazakhstan, Small Hinggang, etc.) A deep metamorphic deposits of early D., represented by Gneis, Metamorphic shale, quartzits, and other rocks.

The most important features of Paleogeography are quite detailed for the late Proterezhoy; With respect to early D. there are only fragmentary information. It is established that in the late protein platform arrays were raised and large areas on them were destroyed; The products of this destruction were filled with all lowering platforms and were demolished into framing defrits, where peculiar formations were formed folded by quartzito sandstone formations. Outlooked parts of the platforms were engaged in small seas in which carbonate rocks with stromatolites were deceived. On most of the platforms, the arid climate dominated on average and late reef. In Wend, the situation changed dramatically. Significant cooling has come, and extensive territories were covered by continental glaciation. In connection with the manifestation of Baikal folding in geosynclinal areas, raised arises that delivered a significant amount of debris material.

Minerals. D. very rich in minerals. The grandiose deposits of iron ores are dedicated (ferricular quartzites and jespilles), aluminum raw materials (kyanite and sillimanis) and manganese ores; Conglomerates D. The largest deposits of gold and uranium ores are connected; with major and ultrasound rocks - large deposits of copper, nickel and cobalt ore; With carbonate rocks - lead-zinc deposits. Pegmatites D. are the main source of mica (muscovite), ceramic raw materials and rare metals. With the upper formations of D., the ancient fields of oil (Irkutsk region of the RSFSR) are connected.

In Edakary (635-541 million years ago), life on Earth consisted mainly of single-cell bacteria and algae, but after the Cambrian period, multicellular and animals began to dominate. Cambrian was the first period (542-252 million years ago), which lasted about 57 million years, and then changed, and periods. In these periods, as well as the next and era prevailed vertebrate animals, which initially developed during the Cambrian.

Climate and geography

Not so much is known about the global climate during the Cambrian period, but unusually high levels of carbon dioxide in the atmosphere (approximately 15 times higher than at present) meant that the average temperature could exceed 50 ° C. About 85% of the ground were covered with water ( Compared with 70% today), most of this area has been occupied by the huge oceans of Pantalass and Japtess; The average temperature of these extensive seas could be in the range from 38 to 43 ° C. By the end of Cambria, 485 million years ago, the main part of the Sushi of the planet was focused on the southern continent of Gondwan, which only recently broke away from even greater pannation to the preceding Proterozoic Eon.

Sea life

Invertebrate

The main evolutionary event of Cambrian was the "Cambrian explosion" - a phenomenon that led to a sharp change in the bodies of invertebrate organisms. This process lasted tens of millions of years.

Opabinia

For some reason, Cambrian has witnessed the emergence of some really bizarre creatures, including five-chapted chickenies, barbed hallucins and large anomalkaris (which were one of the largest animals of that time).

Vivakia

Most of these did not leave any live descendant. This aroused assumptions that it could occur in subsequent geological era, if, say, the "alien" Vivaksia evolved.

Nevertheless, such bright representatives of invertebrates were far from the only forms of life in the ocean. The Cambrian period marked the worldwide spread of early plankton, as well as trilobites, worms, tiny clams and small simplest. In fact, the abundance of these organisms allowed anomalkaris and other animals to flourish; These larger invertebrates were on top and spent all their time, eating smaller invertebrates, which were close proximity to them.

Vertebrae

The Cambrian period marked the appearance of the earliest identified organisms of proto vertebrates, including Piciai, and a little more advanced Myllokunmingia. and Haikouichthys. These three kinds are considered the most first prehistoric fish, although there is another likelihood that earlier candidates from the late Proterezhoy will be discovered.

Vegetable world

There are still some disagreements on whether any real plants have existed during the Cambrian period. If this was so, they consisted of microscopic algae and lichens (which do not have a tendency to fossa). It is known that macroscopic plants, such as seaweed, have not yet developed during the Cambrian period, as evidenced by a noticeable gap in the chronicles of fossils.