Organelles such as mitochondria and flagella most likely also arose in the process of phagocytosis. The predecessors of modern cells, absorbing food, acquired symbionts, friendly microorganisms. They, using nutrients that enter the cytoplasm, began to carry out the functions of regulating various intracellular processes. According to the concept of symbiogenesis, the already named mitochondria and flagella appeared in the cell in this way. Many modern studies confirm the validity of the hypothesis.

Alternatives

The RNA world, as the precursor of all living things, has "competitors". Among them are both creationist theories and scientific hypotheses. For many centuries there was an assumption about the spontaneous generation of life: flies and worms appear in rotting waste, mice in old rags. Refuted by thinkers of the 17th-18th centuries, it received a second birth in the last century in the theory of Oparin-Haldane. According to her, life arose as a result of the interaction of organic molecules in the primordial soup. The assumptions of scientists were indirectly confirmed in the famous experiment by Stanley Miller. It was this theory that was replaced at the beginning of our century by the hypothesis of the RNA world.

In parallel, there is an opinion that life has an originally extraterrestrial origin. Brought it to our planet, according to the theory of Panspermia, all the same asteroids and comets that "took care" of the formation of oceans and seas. In fact, this hypothesis does not explain the appearance of life, but states it as a fact, an integral property of matter.

If we summarize all of the above, it becomes clear that the origin of the Earth and life on it today are still open questions. Modern scientists, of course, are much closer to unraveling all the secrets of our planet than the thinkers of Antiquity or the Middle Ages. However, much still needs to be clarified. Various hypotheses of the origin of the Earth replaced each other at those moments when new information was discovered that did not fit into the old picture. It is quite possible that this may happen in the not so distant future, and then the established theories will be replaced by new ones.

The history of planet Earth, like human life, is filled with various important events and stages of development that have occurred since its birth. Before the planet Earth and all other celestial bodies appeared: planets and stars, clouds of dust flew in space. The blue planet, as well as the rest of the objects of the solar system, including the Sun, as scientists suggest, was formed during the compaction of a cloud of interstellar dust.

The Earth was formed about 10 million years after interstellar dust began to condense. The released heat formed the celestial body from the molten substance. After the planet Earth appeared. The differentiation of the layers of its constituents led to the appearance of an inner core of heavy elements wrapped in a mantle, and the accumulation of light elements on the surface caused the formation of a proto-crust. At the same time, the Moon also appeared, possibly due to a strong collision between the Earth and a huge asteroid.

Over time, the planet cooled, a hardened shell appeared on it - the crust, and subsequently the first continents. From the moment the planet Earth appeared, it was constantly bombarded by meteorites and ice comets, as a result, enough water accumulated on the surface to form seas and oceans. Due to strong volcanic activity and steam, an atmosphere was created in which there was practically no oxygen. Throughout the history of the planet Earth, the continents have been constantly floating on a molten mantle, sometimes connecting, then separating, this has been repeated many times over 4.5 billion years.

Complex chemical reactions caused the appearance of organic molecules interacting with each other, more and more complex molecular structures appeared. As a result, this led to the appearance of molecules capable of self-copying. These were the first steps of Life on Earth. Living organisms developed, bacteria appeared, then multicellular organisms. In the process of life of these organisms, the composition of the atmosphere has changed. Oxygen appeared, which led to the development of a protective layer of ozone.

Life has evolved in numerous forms, the number of species on Earth is amazing in its diversity. Changing environmental conditions throughout the history of the planet led to the emergence of new species, many of which subsequently became extinct, others were able to adapt to the new environment and created the modern biosphere.

About 6 million years ago, after billions of years after the Earth appeared, a branch of primate evolutionary differentiation led to the appearance of humans. The ability to move on hind legs, a strong increase in brain size and the development of speech were the main factors. First, man learned how to make fire, then he achieved success in the development of agriculture. This led to an improvement in life, which led to the formation of communities and after civilizations, with different cultural and religious characteristics. Thanks to their achievements in various fields: science, politics, writing, transportation and communications, humans have become the dominant species on Earth. It is no longer the Earth that forms life forms, a person changes the environment in the process of life. For the first time the history of planet Earth is created by the forces of the creatures that live on it, and it is We who are forced to solve global issues of climate and other environment in order to preserve our habitat.

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.

It is believed that the age of our planet is about 4.54 billion years. This entire time period is usually divided into two main stages: Phanerozoic and Precambrian. These stages are called eons or eonoteme. Eons, in turn, are divided into several periods, each of which is distinguished by a set of changes that have taken place in the geological, biological, atmospheric state of the planet.

1. Precambrian, or Cryptozoic- this is an eon (time interval of 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 eonotemes - katarche and archaea. The latter, in turn, includes 4 eras.

1. Katarchaeus- this is the time of the formation of the Earth, but there was still neither the core nor the earth's crust. The planet was still a cold cosmic body. Scientists suggest that during this period there was already water on Earth. The Catarchean 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, deposits of sulfur, iron, graphite, and nickel were being formed. The hydrosphere and the 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 veil, so darkness reigned on the planet. 2.1 2.1. Eoarchean- this is the first geological era, which lasted about 400 million years. The most important event of the Eoarchean is 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, is formed.

2.2 Paleoarchaean- the next era, which also lasted approximately 400 million years. During this period, the core of the Earth is formed, 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 bacteria that have appeared. The remains of these first forms of the Paleoarchean era of life have been found in Western Australia.

2.3 Mesoarchean also lasted about 400 million years. In the Mesoarchean era, our planet was covered by a shallow ocean. 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 form for the first time on Earth. Biological species are still represented by bacteria and microbial life forms.

2.4 Neoarchean- 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 is 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 first appears, the world ocean reaches almost its present volume. And after the longest Huron 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 former forms of life, due to the increase in oxygen content, practically died out. This period is called the oxygen catastrophe. By the end of the era, the first eukaryotes appear on Earth.

3.2 Mesoproterozoic 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 about 8 parts, the super-ocean 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 flora and fauna are represented mainly by marine species. Only towards the end of the Paleozoic does the development of land begin, and the first vertebrates appear.

The Paleozoic era is conditionally divided into 6 periods.

1. Cambrian period lasted 56 million years. During this period, the main rocks are formed, the mineral skeleton appears in living organisms. And the most important event of the Cambrian is the appearance 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 bone fish in the history of the planet appear. On land, the Silurian is marked by the appearance of vascular plants. Supercontinents converge and form Laurasia. By the end of the period, ice melting was noted, the sea level rose, and the climate became milder.

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

5. Carboniferous period often referred to as carbon. At this time, Laurasia collides with Gondwana and the new supercontinent Pangea appears. A new ocean is also formed - Tethys. This is the time when the first amphibians and reptiles appeared.

6. Permian period- the last period of the Paleozoic, which ended 252 million years ago. It is believed that at this time a large asteroid fell to 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, the most extensive deserts appear that have only existed in the entire history of the Earth's development.

IV. Mesozoic- the second era of the Phanerozoic eon, which lasted almost 186 million years. At this time, the continents acquire almost modern outlines. A warm climate contributes to the rapid development of life on Earth. Giant ferns disappear, and angiosperms appear to replace them. 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 a little over 50 million years. At this time, Pangea begins to split, and the inland seas gradually become smaller and dry up. The climate is mild, the zones are not pronounced. Nearly half of land plants are disappearing as deserts spread. And in the realm of fauna, the first warm-blooded and terrestrial reptiles appear, which became the ancestors of dinosaurs and birds.

2 Jurassic covers a gap of 56 million years. A humid and warm climate reigned on Earth. The land is covered with thickets of ferns, pines, palms, cypresses. Dinosaurs reign on the planet, and numerous mammals have so far been distinguished by their small stature and thick hair.

3 Cretaceous- the longest period of the Mesozoic, lasting almost 79 million years. The split of the continents is practically coming to an end, 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, 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. The continents at this time acquired their modern shape, Antarctica occupied the south pole of the Earth, and the oceans continued to grow. Plants and animals that survived the catastrophe of the Cretaceous period found themselves in a completely new world. Unique communities of lifeforms 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 that time, a tropical climate reigned on Earth, Europe was hiding under evergreen tropical forests, and deciduous trees grew only in the north of the continents. It was during the Paleogene period that the rapid development of mammals takes place.

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 advent 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.

The question of the origin of the Earth, planets and the solar system as a whole has worried people since ancient times. Myths about the origin of the Earth can be traced among many ancient peoples. The Chinese, Egyptians, Sumerians, Greeks had their own idea of ​​the formation of the world. At the beginning of our era, their naive ideas were replaced by religious dogmas that did not tolerate objections. In medieval Europe, attempts to search for the truth sometimes ended in the fire of the Inquisition. The first scientific explanations of the problem belong only to the 18th century. Even now there is no single hypothesis of the origin of the Earth, which gives room for new discoveries and food for an inquisitive mind.

Mythology of the ancients

Man is an inquisitive being. Since ancient times, people differed from animals not only in their desire to survive in the harsh wild world, but also in an attempt to understand it. Recognizing the total superiority of the forces of nature over themselves, people began to deify the ongoing processes. Most often, it is the celestials who are credited with the merit of creating the world.

Myths about the origin of the Earth in different parts of the world differed significantly from each other. According to the ideas of the ancient Egyptians, she hatched from a sacred egg molded by the god Khnum from ordinary clay. According to the beliefs of the island peoples, the gods fished the earth out of the ocean.

Chaos theory

The ancient Greeks came closest to scientific theory. According to their concepts, the birth of the Earth came from the original Chaos, filled with a mixture of water, earth, fire and air. This fits in with the scientific postulates of the theory of the origin of the Earth. An explosive mixture of elements rotated chaotically, filling everything that exists. But at some point, from the bowels of the original Chaos, the Earth was born - the goddess Gaia, and her eternal companion, Heaven, the god Uranus. Together they filled the lifeless spaces with a variety of life.

A similar myth has formed in China. Chaos Hun-tun, filled with five elements - wood, metal, earth, fire and water - circled in the form of an egg through the boundless universe, until the god Pan-Gu was born in it. When he woke up, he found around him only a lifeless darkness. And this fact saddened him greatly. Gathering his strength, the Pan-Gu deity broke the shell of the chaos egg, releasing two principles: Yin and Yang. Heavy Yin descended to form the earth, light and light Yang soared up to form the sky.

Class theory of the formation of the Earth

The origin of the planets, and in particular the Earth, has been sufficiently studied by modern scientists. But there are a number of fundamental questions (for example, where did the water come from) that cause heated debate. Therefore, the science of the Universe is developing, each new discovery becomes a brick in the foundation of the hypothesis of the origin of the Earth.

The famous Soviet scientist, better known for polar research, grouped all the proposed hypotheses and combined them into three classes. The first includes theories based on the postulate of the formation of the Sun, planets, moons and comets from a single material (nebula). These are the well-known hypotheses of Voitkevich, Laplace, Kant, Fesenkov, recently revised by Rudnik, Sobotovich and other scientists.

The second class combines ideas according to which the planets were formed directly from the substance of the Sun. These are the hypotheses of the origin of the Earth by scientists Jeans, Jeffreys, Multon and Chamberlin, Buffon and others.

And finally, the third class includes theories that do not unite the Sun and the planets by a common origin. The best known is Schmidt's conjecture. Let's take a look at the characteristics of each class.

Kant's hypothesis

In 1755, the German philosopher Kant briefly described the origin of the Earth as follows: the original Universe consisted of motionless dust-like particles of various densities. The forces of gravity led them to move. They stick to each other (the effect of accretion), which ultimately leads to the formation of a central hot bunch - the Sun. Further collisions of particles led to the rotation of the Sun, and with it the dust cloud.

In the latter, separate clots of matter gradually formed - the embryos of future planets, around which satellites were formed according to a similar scheme. The Earth formed in this way at the beginning of its existence seemed to be cold.

Laplace's concept

The French astronomer and mathematician P. Laplace proposed a slightly different version explaining the origin of the planet Earth and other planets. The solar system, in his opinion, was formed from a hot gaseous nebula with a bunch of particles in the center. It rotated and contracted under the influence of universal gravity. With further cooling, the speed of rotation of the nebula grew, along the periphery, rings peeled off from it, which disintegrated into prototypes of future planets. The latter at the initial stage were incandescent gas balls, which gradually cooled and solidified.

Lack of Hypotheses of Kant and Laplace

The hypotheses of Kant and Laplace, explaining the origin of the planet Earth, were dominant in cosmogony until the beginning of the 20th century. And they played a progressive role, serving as the basis for the natural sciences, especially geology. The main drawback of the hypothesis is the inability to explain the distribution of angular momentum (MKR) within the solar system.

The MKR is defined as the product of body mass times the distance from the center of the system and the speed of its rotation. Indeed, based on the fact that the Sun has more than 90% of the total mass of the system, it must also have a high MCR. In fact, the Sun has only 2% of the total ICR, while the planets, especially the giants, are endowed with the remaining 98%.

Fesenkov's theory

In 1960, the Soviet scientist Fesenkov tried to explain this contradiction. According to his version of the origin of the Earth, the Sun and planets were formed as a result of the compaction of a giant nebula - "globules". The nebula had very rarefied matter, composed mainly of hydrogen, helium and a small amount of heavy elements. Under the influence of gravitational force in the central part of the globule, a star-shaped condensation appeared - the Sun. It was spinning fast. As a result of the substance, matter was emitted from time to time into the gas-dust environment surrounding it. This led to the loss of its mass by the Sun and the transfer of a significant part of the ISS to the created planets. The formation of the planets took place by means of accretion of matter from the nebula.

Theories of Multon and Chamberlin

American researchers, astronomer Multon and geologist Chamberlin, proposed similar hypotheses for the origin of the Earth and the solar system, according to which the planets were formed from the substance of gas spiral branches, "stretched" from the Sun by an unknown star, which passed at a fairly close distance from it.

Scientists introduced the concept of "planetesimal" into cosmogony - these are clots condensed from the gases of the original substance, which became the embryos of planets and asteroids.

Jeans' judgments

The English astrophysicist D. Jeans (1919) suggested that when another star approached the Sun, a cigar-shaped protrusion broke off from the latter, which later disintegrated into separate clumps. Moreover, large planets were formed from the middle thickened part of the "cigar", and small planets along its edges.

Schmidt's hypothesis

In questions of the theory of the origin of the Earth, an original point of view was expressed in 1944 by Schmidt. This is the so-called meteorite hypothesis, subsequently physical and mathematically justified by the students of the famous scientist. By the way, the problem of the formation of the Sun is not considered in the hypothesis.

According to the theory, the Sun at one of the stages of its development captured (attracted to itself) a cold gas-dust meteorite cloud. Prior to that, it owned a very small MKR, while the cloud rotated at a significant speed. In the strong Sun, the meteorite cloud began to differentiate in terms of mass, density, and size. Part of the meteorite material hit the star, the other, as a result of accretion processes, formed clots-embryos of the planets and their satellites.

In this hypothesis, the origin and development of the Earth is dependent on the influence of the "solar wind" - the pressure of solar radiation, which repelled light gas components to the periphery of the solar system. The earth thus formed was a cold body. Further heating is associated with radiogenic heat, gravitational differentiation and other sources of internal energy of the planet. Researchers consider the very low probability of capturing such a meteorite cloud by the Sun as a big drawback of the hypothesis.

Assumptions by Rudnik and Sobotovich

The history of the origin of the Earth is still of concern to scientists. Relatively recently (in 1984), V. Rudnik and E. Sobotovich presented their own version of the origin of the planets and the Sun. According to their ideas, the initiator of the processes in the gas-dust nebula could be a nearby explosion of a supernova. Further events, according to the researchers, looked like this:

1. Under the action of the explosion, the compression of the nebula began and the formation of a central bunch - the Sun.
2. From the forming Sun, RTOs were transmitted to the planets by electromagnetic or turbulent-convective means.
3. Giant rings began to form, resembling the rings of Saturn.
4. As a result of accretion of the material of the rings, planetesimals first appeared, subsequently formed into modern planets.

The whole evolution took place very quickly - for about 600 million years.

Formation of the composition of the Earth

There is a different understanding of the sequence of formation of the inner parts of our planet. According to one of them, the proto-Earth was an unsorted conglomerate of iron-silicate matter. Subsequently, as a result of gravity, a division into an iron core and a silicate mantle occurred - the phenomenon of homogeneous accretion. Proponents of heterogeneous accretion believe that a refractory iron core accumulated first, then more fusible silicate particles adhered to it.

Depending on the solution of this issue, we can also talk about the degree of the initial heating of the Earth. Indeed, immediately after its formation, the planet began to warm up due to the combined action of several factors:

• The bombardment of its surface by planetesimals, which was accompanied by the release of heat.
• isotopes, including short-lived isotopes of aluminum, iodine, plutonium, etc.
• Gravitational differentiation of interiors (assuming homogeneous accretion).

According to a number of researchers, at this early stage of the formation of the planet, the outer parts could be in a state close to a melt. In the photo, the planet Earth would look like a hot ball.

Contractual theory of the formation of continents

One of the first hypotheses of the origin of the continents was the contraction hypothesis, according to which mountain building was associated with the cooling of the Earth and the reduction of its radius. It was she who served as the foundation of early geological research. On its basis, the Austrian geologist E. Suess synthesized all the knowledge that existed at that time about the structure of the earth's crust in the monograph "The Face of the Earth". But already at the end of the XIX century. data appeared showing that compression occurs in one part of the earth's crust, and tension occurs in the other. The contraction theory finally collapsed after the discovery of radioactivity and the presence of large reserves of radioactive elements in the Earth's crust.

Continental drift

At the beginning of the twentieth century. the hypothesis of continental drift is born. Scientists have long noticed the similarity of the coastlines of South America and the Arabian Peninsula, Africa and Hindustan, etc. The first to compare the data was Pilligrini (1858), later Bikhanov. The very idea of ​​continental drift was formulated by the American geologists Taylor and Baker (1910) and the German meteorologist and geophysicist Wegener (1912). The latter substantiated this hypothesis in his monograph "The Origin of Continents and Oceans", which was published in 1915. Arguments given in support of this hypothesis:

• The similarity of the outlines of the continents on both sides of the Atlantic, as well as the continents bordering the Indian Ocean.
• Similarity of structure on adjacent continents of Late Paleozoic and Early Mesozoic rocks.
• Fossilized remains of animals and plants, which indicate that the ancient flora and fauna of the southern continents formed a single group: this is especially evidenced by the fossilized remains of dinosaurs of the Lystrosaurus genus found in Africa, India and Antarctica.
• Paleoclimatic data: for example, the presence of traces of the Late Paleozoic ice sheet.

Formation of the earth's crust

The origin and development of the Earth is inextricably linked with mountain building. A. Wegener argued that the continents, consisting of fairly light mineral masses, seem to float on the underlying heavy plastic substance of the basalt bed. It is assumed that initially a thin layer of granite material allegedly covered the entire Earth. Gradually, its integrity was broken by the tidal forces of attraction of the Moon and the Sun, acting on the surface of the planet from east to west, as well as by centrifugal forces from the rotation of the Earth, acting from the poles to the equator.

Granite (presumably) consisted of a single supercontinent Pangea. It lasted until the middle and broke up in the Jurassic period. A supporter of this hypothesis of the origin of the Earth was the scientist Staub. Then there was an association of the continents of the northern hemisphere - Laurasia, and an association of the continents of the southern hemisphere - Gondwana. Between them were the rocks of the bottom of the Pacific Ocean. Under the continents lay a sea of ​​magma along which they moved. Laurasia and Gondwana moved rhythmically either to the equator or to the poles. As the supercontinents moved toward the equator, they contracted frontally, while their flanks pressed against the Pacific mass. These geological processes are considered by many to be the main factors in the formation of large mountain ranges. Movement to the equator occurred three times: during the Caledonian, Hercynian and Alpine orogeny.

Conclusion

A lot of popular science literature, children's books, and specialized publications have been published on the topic of the formation of the solar system. The origin of the Earth for children in an accessible form is set out in school textbooks. But if we take the literature of 50 years ago, it is clear that modern scientists look at some problems in a different way. Cosmology, geology and related sciences do not stand still. Thanks to the conquest of near-Earth space, people already know how the planet Earth is seen in the photo from space. New knowledge forms a new idea of ​​the laws of the Universe.

It is obvious that the mighty forces of nature were used to create the Earth, planets and the Sun from the primordial chaos. It is not surprising that the ancient ancestors compared them with the accomplishments of the Gods. Even figuratively it is impossible to imagine the origin of the Earth, pictures of reality would surely surpass the most daring fantasies. But by bits of knowledge collected by scientists, a complete picture of the surrounding world is gradually being built.

The main document by which the history of the Earth is explored is the rock.

The oldest evidence at our disposal dates back to Archean times. They are the starting points for the historian of the Earth, but it is obvious that although many of the ancient rocks (for example, uraninite from Manitoba) were formed about 2 billion years ago, they cannot at all be considered as the real beginning of the geological record. It is necessary to restore this beginning in indirect ways.

Two fundamental problems need to be elucidated: the origin of the Earth and the emergence of life on it. Generations of scientists worked on these questions, but only Soviet science, armed with the method of dialectical materialism, was able to unravel both world riddles in a general form.

The most reliable theory of the origin of the planets of the solar system was developed by O. Yu. Schmidt. The theory proceeds from the fact of the rotation of the Galaxy and the presence of dark clouds of cosmic dust and gas in its central plane. The sun, participating in the galactic rotation, captured and dragged away a part of such a cloud. It is also possible that the Sun itself arose from such a cloud and captured matter from its own mother environment. But in both cases, it was inside a vast swarm of solid particles moving around it under the influence of gravity in elliptical orbits. Dust particles, solid bodies, colliding in inelastic impacts, lost part of their kinetic energy (it turned into heat radiated into space), which led first to the swarm compaction, and when the latter reached a certain critical density, to the formation of clusters, which, repeatedly breaking up and united again, eventually formed into planets.

Near the Sun, the captured cloud quickly thinned out: some of its particles fell on the Sun, while others were pushed aside by the radiation pressure to the outer zone of the system; volatile components of solid bodies evaporated under the action of solar heating. That is why dense, but relatively small planets were formed near the Sun, and far from it, where there was no such depletion of the source material and gases were preserved in solid particles, planets large, but much less dense, arose. This explains the characteristic division of the planets into internal (Mercury, Venus, Earth, Mars), which have small sizes, high density, slow rotation around the axis and a limited number (or absence) of satellites, and external (Jupiter, Saturn, Uranus, Neptune) , characterized by large size, low density, fast rotation on the axis and a large number of satellites. At the farthest outskirts of the cloud, where the parent swarm came to naught, a small Pluto arose from its remnants (and, possibly, several other small planets, not yet discovered).

The particles captured by the Sun could initially move in different planes, but still, most of the orbits should have coincided with some dominant plane. In relation to the predominant plane, the particles could first move both in the forward and in the opposite direction, but, due to the uneven distribution of the swarm density, here one of the directions should have become dominant. Finally, the elliptical particle orbits could initially have differently oriented axes; however, interacting during approach, the bodies mutually perturbed their orbits, which led to a uniform distribution of the axes, i.e., gave the orbits a circular (or very close to it) shape. So, by averaging the dynamic and physical characteristics of dust particles when they stick together into larger bodies, the theory of O. Yu. Schmidt explains the fact that all planets revolve around the Sun in the same direction and have almost identical circular orbits lying almost in the same plane.

None of the numerous previous hypotheses could explain the distribution of angular momentum inherent in the solar system: the Sun, which has 99% of the total mass of the system, contains only 2% of the angular momentum, while the planets with their negligible total mass have together 98% of the angular momentum . The angular momentum is the product of the body's mass times its speed times its distance from the center of rotation. In a system of bodies, the moment of momentum is the sum of the moments of individual bodies. Schmidt's theory completely solves the problem. Dusty matter could be captured by the Sun both at a close and at a far distance. In the latter case, it will have a very large angular momentum. When adding particles into planets, this moment is preserved.

Finally, the theory for the first time scientifically substantiates the law of planetary distances, established a long time ago purely empirically, but until recently not amenable to interpretation, and predicts that the distances of the planets from the Sun (in astronomical units) should be as follows: Mercury 0.39, Venus 0.67, Earth 1.04, Mars 1.49, Jupiter 5.20, Saturn 10.76, Uranus 18.32, Neptune 27.88 and Pluto 39.44. Comparison with actual distances reveals an excellent match.

The formation of planetary systems in the depths of our and other galaxies is natural and inevitable, since there are many clouds of dark matter in the universe, and stars either arise from these clusters or meet them during their movement. We do not see other planetary systems only because modern astronomical means of observation do not allow it.

It follows from the theory of O. Yu. Schmidt that the Earth arose as a cold body, since the particles of the swarm that gave rise to it, due to the balance between their absorption of solar heat and its return radiation into space, had a temperature of about + 4 °. The current heat inside the Earth is the result of subsequent heating under the influence of the decay of radioactive substances. The earth was created by the random accumulation of particles of the most varied specific gravity. When the planet reached a certain size, gravitational differentiation began in a viscous medium: denser substances very slowly began to sink towards the center of the Earth, lighter substances floated upward, carrying with them some heavy minerals (including radioactive ones) geochemically associated with them, which explains the current concentration the latter in the outer layers). This process is unlikely to have ended, and differentiation, accompanied by the release of no less energy than radioactive decay (of the order of 6 X 10 27 ergs, or 10 20 calories per year), still plays the role of a powerful mechanism for vertical movements of masses in the bowels of the earth.

At a certain stage (when the mass of the Earth became significant) the atmosphere was formed. There were also gases in the dust cloud captured by the Sun, but still, the primary atmosphere was mainly formed as a result of “squeezing out” gases from the bowels of the planet. The source of the earth's atmosphere is the earth itself. The most ancient atmosphere differed from the current one in that it lacked free nitrogen and oxygen, but there was a lot of water vapor, ammonia and carbon dioxide.

The emergence of sources of internal energy - radioactive decay and gravitational differentiation - marked the beginning of the tectonic activity of the Earth, - the uplift and lowering of vast areas of the cold earth's surface and the processes of volcanism; igneous rocks appeared. Water accumulated in the depressions of the lithosphere - the separation of land and sea was indicated. Under the action of water, air and solar radiation, the processes of weathering, the transfer of detrital material and the formation of the first sedimentary rocks began.

It is not known when the dawn of life began over the desert Earth, but it probably happened before the Archean. There are no reliable remains of organisms in the Archean strata themselves, however, there are calcareous and carbonaceous rocks, the occurrence of which is most often associated with the activity and death of animals and plants. In addition, the organisms found in the Proterozoic are distinguished by a complex structure and must have had ancestors that were much simpler; if these ancestors lived in the Archean, then life should have appeared even earlier.

Life in the forms in which we know it is possible only on planets and, moreover, under very specific conditions. Its existence somewhere on hot bodies (stars) or in interstellar space is incredible: in the first case, high temperatures interfere, in the second case, metabolism is unthinkable. But not all planets have the environment necessary for life: some of them, located close to the star, are too hot, others, which lie far from the star, are too cold; some planets have lost their atmosphere, while others have it made up of poisonous gases. Only on a solid surface, in the presence of water and air of a favorable composition and in the presence of an appropriate temperature regime, the first lumps of protoplasm can appear. In the solar system, life is flourishing on Earth, dying out on Mars, and nascent on Venus. Despite these limitations of the conditions for life, life in the world cannot be an exceptional phenomenon, characteristic only of the vicinity of our Sun: even if in each galaxy there is at least only one planet inhabited by organisms, the number of such centers of life in the infinite Universe is incalculable.

Living matter is a special stage in the development of inorganic matter. Life really arose, and did not exist forever, as some authors claim. The idea of ​​the eternity of life, i.e., of the original existence (along with simple, unorganized matter) of such complex formations, which include even the simplest protein molecules, denies the development of matter, i.e., is directed contrary to the truth, scientifically substantiated and proven.

The discovery of common ways of the origin of life on Earth belongs to the Soviet scientist A. I. Oparin.

The theory of A. I. Oparin is based on the facts of the wide distribution in the universe of carbon (the main element from which organic substances are built) and the high ability of carbon atoms to combine with each other or with atoms of other elements. In various types and compounds, carbon is found in stars, on planets and in meteorites, in the latter either native (graphite, diamond) or in the form of carbides (compounds with metals) and hydrocarbons. There is no reason to deny the presence of carbon in the particles of dusty matter from which the Earth was formed; The presence of hydrogen, methane, ammonia, and water (ice) has recently been established in the gas-dust nebulae that currently exist in the Galaxy. Therefore, carbon and its simplest compounds in the form of hydrocarbons became part of our planet in the very first days of its birth.

The history of carbon on Earth is at first the history of countless chemical reactions and the further interaction of hydrocarbons with water vapor and ammonia. As a result, new, more complex substances arose, already built from carbon, oxygen, hydrogen and nitrogen, capable of new reactions with each other and with the environment in the primary seas and lagoons, where they got from the atmosphere. In the chaos of these reactions, eventually, a path was outlined for the formation and accumulation of more and more complex macromolecular compounds, including those similar to proteins.

In a mixed solution of protein substances, molecules of different proteins usually gather into small aggregates that look like drops floating in water - this phenomenon is called coacervation. And if the primary, simpler organic compounds were evenly dispersed in water and were not isolated from the latter, then after the appearance of protein-like compounds, a significant leap occurred: the separation of coacervate drops began, i.e., the opposition of protein-like compounds to their environment. A coacervate drop is already something individual, having its own, albeit still unstable, structure; each one easily attracts particles from the outside, absorbs them, enters into chemical compounds with them, which may remain in the drop, and therefore lead it to growth and internal chemical restructuring or to decay. If synthesis in a drop under given environmental conditions is faster than decay, the drop becomes dynamically stable; if decay is faster than synthesis, it collapses. In coacervate drops, nature, as it were, makes the first experiments on metabolism. Only dynamically stable drops (which depended on their individual characteristics) could exist for a long time, grow and “reproduce” by division, and only those few could become such, the qualities of which continuously changed in a completely definite direction, ensuring constant self-recovery of the entire drop as a whole. The emergence of a drop with an internally organized sequence of chemical reactions, i.e. a drop that is dynamically very stable and capable of self-reproduction, was that new leap, as a result of which a complex but inanimate organic formation became a living being. According to some biologists, the acquisition by protein-like compounds in the course of their development of the main features of living things does not require the stage of complex “supramolecular” protein systems (coacervate drops): such features should inevitably arise under certain conditions in the primary protein molecule itself.

Lumps of primeval life did not yet have a cellular structure; millennia passed before the most ancient unicellular organisms, the ancestors of multicellular organisms, developed. Thousands of years also passed before the way of nutrition of the first organisms changed, which at first used only organic substances for this purpose, but then, due to a decrease in the supply of this food, they were, as it were, faced with a choice: either die or acquire the ability to eat inorganic compounds. . Subsequently, pigments were developed in the protoplasm of one group of organisms, which served as an impetus for the appearance of simple plants such as blue-green algae, capable of assimilating CO 2 . Algae not only dramatically increased the amount of organic matter in nature, but also freed other groups of living beings from the need to evolve towards autotrophy; these groups, now feeding on algae, remained heterotrophic and thus became the ancestors of the future animal world.

The sea is considered the cradle of life. This assumption, although questioned, has never been refuted by convincing arguments. The sea is an exceptionally suitable environment for the development of organisms: water, as a mobile element, provides an influx of food even for sessile or passively swimming organisms; the sea contains in huge quantities a wide variety of substances necessary for organisms; Finally, the significant stability of the physical conditions and chemical composition of sea water makes the exchange of substances between the organism and the environment not a random process, but a regular one and, moreover, proceeding under constantly favorable conditions. However, we are talking primarily about the coastal parts of the sea, where the interaction of the lithosphere, hydrosphere and atmosphere, i.e., the whole sum of geographical conditions, most contributes to the maintenance of life.

We have tried to draw a probable picture of the development of the Earth and its landscape envelope over the vast period preceding the Archean. During this period of time, covering 3-4 billion years, the Earth went through the following stages:

1. The stage of the initial clot of matter in the parent dust cloud.

2. The stage of a small planet (comparable in volume to the current Mercury), already capable of holding a permanent gaseous shell around itself. The beginnings of tectonic activity (sources of energy: the decay of radioactive substances and, possibly, the beginning of gravitational differentiation). Emission of gases H 2 O, CO 2 and NH 3 with igneous rocks and their inclusion in the composition of the primary atmosphere.

3. The earth reaches its present size. Its outer stone shell is probably of basalt composition. Accumulation of inanimate organic matter and its development towards the formation of macromolecular compounds.

4. Emergence of precellular life forms. Organisms are only heterotrophic.

5. The emergence of unicellular organisms and the emergence of a branch of autotrophic living beings. Enrichment of the atmosphere with free oxygen and nitrogen due to the vital activity of microorganisms.

Let us now turn to the later periods of the life of the Earth. Despite the paucity of materials, we still have many quite reliable facts here, on the basis of which we can draw fairly reliable general conclusions. The development of the landscape shell over the course of geological time is divided into several stages: the most ancient and poorly known ones are conveniently grouped under the collective name "Precambrian"; they are followed by the Caledonian, Hercynian (or Variscan) and Alpine stages.