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 creature. 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 planet 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 beliefsisland peoples, the earth was fished out of the ocean by the gods.
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, the Sky, the god Uranus. Together, they filled the lifeless expanses 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 upwards 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 Otto Yulievich Schmidt, better known for polar research, grouped everythingproposed hypotheses and grouped 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 dwell on 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 were 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
French astronomer and mathematician P. Laplace proposed a somewhat differenta variant 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 hot gas balls, which gradually cooled and solidified.
The 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 twentieth 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.
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 MKR, 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 anda 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 evolution of solar matter into the surrounding gas-dust environment, matter was emitted from time to time. This led to the loss of its mass by the Sun and the transfer of a significant part of the ICR to the created planets. The formation of the planets took place by accreting the matter of the nebula.
Multon and Chamberlin's theories
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 Judgment
The English astronomer and physicist 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 clots. Moreover, large planets were formed from the middle thickened part of the "cigar", and small ones along its edges.
Schmidt's Hypothesis
In questions of the theory of the origin of the Earth, the original point of view was expressed in 1944 by Schmidt. This is the so-called meteorite hypothesis, which was subsequently substantiated in physical and mathematical terms by the students of the famousscientist. 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 gravitational field of the 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 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. The 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 still excites 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:
- Under the action of the explosion, the compression of the nebula began and the formation of a central clot -Sun.
- From the forming Sun, MRK was transmitted to the planets by electromagnetic or turbulent-convective way.
- Giant rings began to form, resembling those of Saturn.
- As a result of the accretion of the material of the rings, planetesimals first appeared, later formed into modern planets.
The whole evolution took place very quickly - for about 600 million years.
Formation of the composition of the Earth
There are different understandings 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. Later, 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 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 with planetesimals, which was accompanied by the release of heat.
- The decay of radioactive isotopes, including short-lived isotopes of aluminum, iodine, plutonium, etc.
- Gravity differentiation of subsoil (assuming homogeneous accretion).
According to some researchers, at this early stageDuring the formation of the planet, the outer parts could be in a state close to melting. In the photo, the planet Earth would look like a hot ball.
Contract theory of the formation of continents
One of the first hypotheses of the origin of the continents was contraction, 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 have 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 Africa, Africa 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 Indianocean.
- Similarities of structures on adjacent continents of geological sections of Late Paleozoic and Early Mesozoic rocks.
- The 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 bas alt bed. It is assumed that initially a thin layer of granite material allegedly covered the entire Earth. Gradually, its integrity was violated 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 the centrifugal forces from the rotation of the Earth, acting from the poles to the equator.
From granite (presumably) consisted of a single supercontinent Pangea. It existed until the middle of the Mesozoic era 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 rhythmicallymoved to the equator, then 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, 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 understanding 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 bits of knowledge collected by scientists are gradually building a complete picture of the world around us.
