History of the Earth
Only relatively recently did people receive factual material that makes it possible to put forward scientifically grounded hypotheses about the origin of the Earth, but this question has worried the minds of philosophers since time immemorial.
First performances
Although the first ideas about the life of the Earth were based only on empirical observations of natural phenomena, nevertheless, fantastic fiction rather than objective reality often played a fundamental role in them. But already in those days, ideas and views arose, which in our days amaze us with their similarity with our ideas about the origin of the Earth.
So, for example, the Roman philosopher and poet Titus Lucretius Carus, who is known as the author of the didactic poem "On the Nature of Things", believed that the Universe is infinite and there are many worlds similar to ours. The ancient Greek scientist Heraclitus (500 BC) wrote about the same: “The world, one of everything, was not created by any of the gods or any of people, but was, is and will be an eternally living fire, naturally flammable and naturally extinguished ".
After the fall of the Roman Empire for Europe came a difficult time of the Middle Ages - the period of the dominance of theology and scholasticism. This period then gave way to the Renaissance, the works of Leonardo da Vinci, Nicolaus Copernicus, Giordano Bruno, Galileo Galilei prepared the emergence of progressive cosmogonic ideas. They were expressed at different times by R. Descartes, I. Newton, N. Steenon, I. Kant and P. Laplace.
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Hypotheses of the origin of the Earth
R. Descartes's hypothesis
• So, in particular, R. Descartes argued that our planet was previously a red-hot body, like the Sun. And subsequently it cooled down and began to represent itself as an extinct celestial body, in the depths of which fire was still preserved. The incandescent core was covered with a dense shell, which consisted of a substance similar to that of sunspots. Above, there was a new shell - made of small fragments resulting from the disintegration of spots.
I. Kant's hypothesis
• 1755 - the German philosopher I. Kant suggested that the substance of which the body of the solar system - all planets and comets - was decomposed into primary elements before the start of all transformations and filled the entire volume of the Universe in which the bodies now formed from them move … These ideas of Kant that the solar system could have been formed as a result of the accumulation of primary dispersed scattered matter seem surprisingly correct in our time.
P. Laplace's hypothesis
• 1796 - the French scientist P. Laplace expressed similar ideas about the origin of the Earth, knowing nothing about the existing treatise by I. Kant. The hypothesis that appeared about the origin of the Earth was thus called the Kant-Laplace hypothesis. According to this hypothesis, the Sun and the planets moving around it were formed from a single nebula, which, when rotating, disintegrated into separate clumps of matter - planets.
Initially, the fiery liquid Earth cooled down, covered with a crust, which warped as the depths cooled and their volume decreased. It should be noted that the Kant-Laplace hypothesis has prevailed in a number of other cosmogonic views for more than 150 years. It was on the basis of this hypothesis that geologists explained all the geological processes that took place in the bowels of the Earth and on its surface.
E. Chladni's hypothesis
• Of great importance for the development of reliable scientific hypotheses about the origin of the Earth are of course meteorites - aliens from distant space. All due to the fact that meteorites have always been falling on our planet. However, they were not always considered aliens from outer space. One of the first to correctly explain the appearance of meteorites was the German physicist E. Chladni, who proved in 1794 that meteorites are the remnants of fireballs of unearthly origin. According to him, meteorites are pieces of interplanetary matter wandering in space, probably also fragments of planets.
The modern concept of the origin of the Earth
But this kind of thought in those days was not shared by all, however, studying stone and iron meteorites, scientists were able to obtain interesting data that were used in cosmogonic constructions. For example, the chemical composition of meteorites was found out - basically it turned out that these were oxides of silicon, magnesium, iron, aluminum, calcium, sodium. Consequently, it became possible to find out the composition of other planets, which turned out to be akin to the chemical composition of our Earth. The absolute age of the meteorites was also determined: it is in the range of 4.2-4.6 billion years. At the moment, these data have been supplemented with information on the chemical composition and age of the rocks of the Moon, as well as the atmospheres and rocks of Venus and Mars. These new data show, in particular, that our natural satellite Luna was formed from a cold cloud of gas and dust and began to "function" 4,5 billion years ago.
A huge role in substantiating the modern concept of the origin of the Earth and the solar system belongs to the Soviet scientist, academician O. Schmidt, who made a significant contribution to solving this problem.
So bit by bit, according to separate scattered facts, the scientific basis of modern cosmogonic views was gradually formed … Most modern cosmogonists adhere to the following point of view.
The initial material for the formation of the solar system was a gas-dust cloud located in the equatorial plane of our Galaxy. The substance of this cloud was in a cold state and contained, as a rule, volatile components: hydrogen, helium, nitrogen, water vapor, methane, carbon. The primary planetary matter was very homogeneous, and its temperature was rather low.
Due to the forces of gravity, interstellar clouds began to shrink. The substance became denser to the stage of stars, at the same time its internal temperature increased. The movement of the atoms inside the cloud accelerated, and, colliding with each other, the atoms sometimes combined. Thermonuclear reactions took place, during which hydrogen was converted into helium, while a huge amount of energy was released.
In the fury of powerful elements, the Protosun appeared. Its birth occurred as a result of a supernova explosion - a phenomenon not so rare. On average, such a star appears in any galaxy every 350 million years. During a supernova explosion, gigantic energy is emitted. The material ejected as a result of this thermonuclear explosion formed a wide, gradually condensing gas plasma cloud around the Protosun. It was a kind of nebula in the form of a disk with a temperature of several million degrees Celsius. From this protoplanetary cloud, planets, comets, asteroids and other celestial bodies of the solar system arose later. The formation of the Protosun and the protoplanetary cloud around it occurred possibly about 6 billion years ago.
Hundreds of millions of years have passed. Over time, the gaseous matter of the protoplanetary cloud cooled down. The most refractory elements and their oxides were condensed from the hot gas. As the cooling continued for millions of years, dust-like solid particles appeared in the cloud, and the previously incandescent gas cloud became comparatively cold again.
Gradually, a wide annular disk was formed around the young Sun as a result of the condensation of dusty matter, which subsequently disintegrated into cold swarms of solid particles and gas. From the inner parts of the gas-dust disk, Earth-like planets began to form, usually consisting of refractory elements, and from the peripheral parts of the disk, large planets rich in light gases and volatile elements. In the very outer zone, a huge number of comets appeared.
Primary Earth
So about 5.5 billion years ago, the first planets arose from the cold planetary matter, including the primary Earth. In those days, it was a cosmic body, but not yet a planet, it did not have a core and mantle and did not even have solid surface areas.
The formation of Proto-Earth was an extremely important milestone - it was the birth of the Earth. In those days, ordinary, well-known geological processes did not occur on Earth, therefore this period of the planet's evolution is called pre-geological, or astronomical.
Proto-earth was a cold accumulation of cosmic matter. Under the influence of gravitational compaction, heating from the continuous impacts of cosmic bodies (comets, meteorites) and the release of heat by radioactive elements, the surface of Proto-Earth began to heat up. There is no consensus among scientists about the amount of warming up. According to the Soviet scientist V. Fesenko, the substance of Proto-Earth heated up to 10,000 ° C and, as a consequence, passed into a molten state. According to the assumption of other scientists, the temperature could barely reach 1,000 ° C, and still others deny even the very possibility of melting the substance.
Be that as it may, but the warming up of Proto-earth contributed to the differentiation of its material, which continued throughout the entire subsequent geological history.
Differentiation of the substance of Proto-Earth led to the concentration of heavy elements in its inner regions, and on the surface - lighter ones. This, in turn, predetermined the further division into core and mantle.
Initially, our planet had no atmosphere. This can be explained by the fact that gases from the protoplanetary cloud were lost in the first stages of formation, because then the mass of the Earth could not keep light gases near its surface.
The formation of the core and mantle, and later the atmosphere, completed the first stage of the Earth's development - pre-geological, or astronomical. The earth has become a solid planet. After that, its long geological evolution begins.
Thus, 4-5 billion years ago, the solar wind, hot rays of the Sun and cosmic cold dominated the surface of our planet. The surface was constantly bombarded by cosmic bodies - from dust particles to asteroids …
A. Voitsekhovsky