When you go out on an early frosty morning and feel crackling snowflakes under your feet or you meet a sunrise on the river bank in the hot July, it is very difficult to imagine that once upon a time nothing of this happened. Nothing at all: no snow, no river, no grass, not even the Sun. There was only an endless space in which dust particles rushed, crashing into each other at huge speeds. This period is difficult to name. It’s not prehistoric, it’s kind of extra-historical: it happened so incomprehensibly long ago, and then space was so hopelessly lifeless ...
However, the origin of the Earth is inextricably linked with this stage of the formation of the universe. The conditions that subsequently led to the appearance of our planet began to form from the very moment of the Big Bang. Various hypotheses of the origin of the Earth and the origin of the world have arisen in the minds of people since when a person first thought about his place in the Universe and about what exists outside the territory familiar to him.
Mythology
All nations have legends about the emergence of peace. They are united by the divine principle underlying the mythological creation. The first deities emerge from chaos, which give rise to the doubt of supernatural beings, as well as everything that is: the ocean, land, day and night, people. The concepts of the origin of the Earth among different peoples are often associated with the desire of God to create a firmament in the middle of world waters. In different eras, myths about the creation of the world were supplemented, or new versions appeared. So, in Hinduism, the origin of the Earth and the entire universe is considered in five versions. According to various legends, the basis for the universe is considered to be the sacred sound of Om, the first man of Purusha, who sacrificed parts of his body to create the world, the breath of Maha-Visnu. Also, the "primary heat" and the "cosmic egg" act as the beginning of all things.
Cosmogony of the Slavs
The origin of the Earth according to the ancient Slavs is in many ways similar to other mythological ideas. Initially, the universe was not ordered. At that time there was only one god, Rod, who structured the primordial Chaos. He created the earth from a combination of sea and heaven. Then his son Svarog began to organize the space. He breathed life into everything earthly, created man, and explained to the first people the laws by which to live.
Under the influence of Christianity, the myth has somewhat changed. In the annals there is a legend about God floating on the pristine waters in a boat and meeting a devil. God sends a demon to the bottom of the sea for a handful of sand and creates earth from it.
Title
The origin of the name “Earth” is also connected with mythological legends about the world order. In the thinking of the distant ancestors of all modern peoples there was no idea of ​​the spherical shape of the planet, and of the planet itself too. The origin of the name “Earth” is associated, on the one hand, with the legend of a flat, like a saucer, surface with land and seas resting on the backs of giant animals. Different peoples had elephants, a turtle or a whale. On the other hand, the origin of the word "earth" is connected with the division of the universe into three levels: the sky, space, inhabited by people and animals, and the underworld, or the underworld. Both of these points influenced the appearance of the familiar designation of our planet in different languages. The origin of the name "Earth" among the ancient Slavs is associated with the concepts of "bottom" and "soil". The earth is that under the sky, below: the soil underfoot, the foundation. Thus, the origin of the name “Earth” is based on an understanding of the world of people as a “flat saucer” and as a space located below the heavenly dwelling place of the gods.
In addition, in the culture of our ancestors, the word "land" was correlated with everything native, with familiar territory. Alien and often hostile was designated as distant, and its name had a similar origin. "For distant lands" - phraseology, meaning "very far away." The ancient Slavs often designated the kingdom of the dead as well.
It is interesting that the roots, from which the name of the planet in other languages ​​originated, are similar in importance to the Slavic. So, the origin of the word "Earth" in English is also associated with the concept of bottom and soil underfoot.
How something came out of nothing
Naturally, modern scientific ideas about the appearance of the Universe are very different from those that underlie any religion. Today, all models of the universe are based on the Big Bang theory. According to her, about 13.77 billion years ago, the Universe arose as a result of an explosion that was hard to imagine in its power. The state in which she was until this moment is called singular. In its characteristics, it was so different from everything that is now known that even scientists can hardly understand what processes took place in it.
Shortly after the Big Bang, the young Universe began to expand. Huge temperature indicators and the speed of its constituent particles did not allow them to combine into larger objects. However, with expansion, the temperature decreased. About a million years passed before the Universe cooled to 4000 Âş, and elementary particles began to form atoms. Helium and hydrogen appeared first, followed by the formation of atoms of heavier elements.
At the next stage in the development of the Universe, the dust and gas particles that made it up began to collide and form larger objects. Slowly forming galaxies with stars and planets. At the same time, the Universe continued to expand, and this process is still ongoing.
Native Slice of the Milky Way
The presentation “The Origin of the Earth" in lessons often begins with a story about the history of the solar system. It started about 4.6 billion years ago. The same processes led to the appearance of our piece of the Galaxy, as a result of which many parts of the Universe were formed. The Milky Way itself appeared about 7-8 billion years earlier. The formation of the solar system was caused by the gravitational collapse of a relatively small portion of the molecular interstellar cloud. Understanding the processes that took place then in this place of the Universe is a rather difficult task due to their remoteness in time. One can only judge the events that triggered the formation of the solar system in a form known to us only by building theories on the basis of the studied cosmic and physical laws and correlating their conclusions with what we actually observe.
Hot hypothesis
At the end of the 19th century, the origin of the Earth and the entire solar system was actively studied by astronomers T. Chamberlain and F. Multon. They put forward the so-called hot hypothesis. They were prompted by the discovery made at that time to create the theory. It became known that deep under the surface of the Earth there is literally hellish heat: the temperature of the subsoil reaches 1000 Âş.
The “hot” hypothesis suggests that the Earth, like other planets, was originally a hot ball, which then gradually began to cool. The appearance of these hot clumps of matter was explained by the interaction of the young Sun with another object comparable in strength to gravitational attraction. The star passed in relative proximity to our star. As a result, something like a bridge was formed between them, consisting of the substance of both cosmic bodies. Gradually the stars parted, and the bridge fell apart into separate hot "islands" of matter, called planetesimals. They subsequently became the planets and satellites known now.
It was cold at first
However, this is far from the only theory explaining the origin of the Earth. Hypotheses in the scientific world begin to dominate when they explain a large number of visible facts. In the second half of the last century, astronomers and physicists turned their attention again to the concept of initially cold planets.
Nebular theory was first formulated in the 18th century. Presumably, it was expressed by Emanuel Swedenborg, then was picked up by Immanuel Kant. The hypothesis was mainly developed in the writings of Pierre-Simon Laplace. According to this theory, the stages of the origin of the Earth and the solar system as a whole were built somewhat differently than in the one described above, and the first of them was the formation of a nebula, or nebula. It was a gas and dust clot concentrated as a result of the collapse of a section of the molecular interstellar cloud. Nebula, due to the influence of gravity from neighboring similar formations, began to rotate. Gravity appeared in the nebula due to rotation, which led to a decrease in its radius. The consequence of this was an increase in speed. The young nebula resembled a centrifuge, and its initially close-to-ball shape became more and more like an ellipse. After some time, the centrifugal force at the equator balanced the force of attraction, and rings began to peel off one after another from the middle zone of the nebula. They consisted of all the same particles of dust and gas, which gradually began to merge into larger objects. Over time, they "grew" to the planets, and the temperature of the new cosmic bodies did not allow them to be called hot.
Subsoil heat
Today, the nebular theory is considered the most likely scenario for the formation of the solar system. The development of the hypothesis took place with the participation of many scientific disciplines, some of the provisions of Laplace were changed or supplemented. The heat of the earth's interior has also received an explanation that does not contradict the theory.
There are two main reasons for warming up: radioactive decay and gravitational differentiation of the bowels. The first gives about 15% of the warm-up. The main importance is the separation of the initially mixed elements into several layers under the action of gravity. This process led not only to an increase in the temperature of the bowels, but also to the formation of the internal structure of the planet that we all study in school: the core, mantle, and crust.
Young Earth was a space object close to the ball in shape, consisting of several randomly mixed elements. Modern observations, however, show that the structure of the planet has a fairly ordered structure. The main elements that make up the Earth are oxygen in the composition of oxides, silicon, iron and aluminum. Each of them in this case affects the density of the substance.
Differentiation
The mass and volume of the Earth, determined as far back as the 18th century, allowed scientists to calculate its average density. It turned out to be approximately 5.5 g / cm 3 . Moreover, the value of the parameter for the surface is only 2.8 g / cm 3 . The values ​​found suggest that the heavier elements are concentrated in the center of the globe, and the light constitute the surface layers.
The ordering of the elements began from the very moment the planet appeared. Under the influence of gravity, the iron began to “settle” to the center, and the compounds of aluminum and silicon, on the contrary, “float” to the surface. Iron, changing its position, shifts the center of gravity of the planet. Due to certain physical laws, a large amount of thermal energy is released, which leads to heating of the inner layers of the Earth. The amount of energy generated is huge. However, studies show that the planet has never been completely molten. This once again confirms the nebular hypothesis.
Cooling and heating
Of course, the heat of the bowels is constantly spent on heating the surface, and part of the energy is lost. However, it is successfully compensated by solar radiation. The energy of differentiation is used in all processes taking place on Earth: the movement of continents, the formation of mountains, and volcanism.
According to scientists, to date, the process of separation of elements completed by 85%. After differentiation ends, the Earth will become a geologically inactive planet, similar in this respect to the Moon. This will happen in about 1.5 billion years.
Bombardment
In addition to the differentiation of the bowels and decay of radioactive elements in the first stages of the formation of the Earth, asteroids played a certain role in the heating of its inner layers. The increase in temperature was facilitated by the frequent collisions of small space bodies with the planet. According to one version, the most impressive of these collisions led to the appearance of the moon. A body the size of Mars collided with Earth. As a result, a rather impressive piece of matter was knocked out of the planet, which subsequently became a satellite. The collision had other results: the Earth's rotation speed increased markedly and its axis bent. Asteroids and comets are also considered one of the likely sources of water.
The appearance of life-giving moisture
The origin of water on Earth is a rather extensive topic. The most probable today is considered the version of its "delivery" by asteroids. Indirectly, the hypothesis is supported by data from space research, which resulted in the discovery of water on several small bodies of the solar system. Scientists who are inclined to this version indicate that water is a rather volatile substance, and therefore, in the hot conditions of a young Earth, it would most likely have completely evaporated. Hence the low probability of terrestrial origin of water. Probably, the substance so necessary for all living things fell on a planet with astroids and comets from the main belt located between Mars and Jupiter.
However, the exact origin of water on Earth is still a question without a clear answer. It is believed that several factors played a role in this process. Among them is the degassing of magma, the smelting of volatile elements from it. Water vapor and some other compounds were released to the surface of the Earth during the eruption of volcanoes. Then the vapors condensed, the oceans gradually accumulated, and the hydrosphere formed.
The appearance of water, as well as the problem of the origin of the Earth, is not a fully resolved issue. Both processes probably played a role here: both the bombardment and the degassing of magma. The latter also contributed to the formation of the atmosphere.
Origin of living on earth
Another widely discussed issue related to the history of the development of the Earth is the appearance of living organisms. Today, there are several hypotheses that describe the origin of life on Earth. Biology, taught ten years ago, opened the curtain of secrets to students: life appeared in the waters of the oceans, in the so-called primary broth. Since then, the picture has changed somewhat, overgrown with new data.
The lesson "The Origin of Life on Earth" today begins with a story about the RNA world. According to recent studies, ribonucleic acid is the first molecule on the planet with the ability to reproduce itself. The next step on the way from the inanimate world to the organic was the acquisition of borders. RNA molecules, probably, in one way or another were inside hollow spheres, which are formed by fatty acids in the ocean. So a prototype of the simplest cell appeared: an RNA molecule surrounded by a membrane.
The formation of metabolism between the external environment and RNA became possible due to the ability of the latter to attract some nucleotides and repel others. The origin of life on Earth, biology and related sciences have not yet been fully studied. There are many outstanding questions. Among them, for example, the occurrence of fission and the formation of multicellular organisms.
Great symbiosis
Less obscure today is the history of various organelles in the cell. It all started with the appearance in the first microorganisms of the ability to phagocytosis, the absorption of nutrients from the environment with the formation of food vacuoles. A new way of feeding has led to an increase in cell size: the predator should be larger than the prey. In this case, the hereditary material was stored in the form of geneophores, the precursors of chromosomes. They were attached directly to the membrane. Phagocytosis was accompanied by the appearance of a strong current in the cytoplasm, in the area of ​​which there were also geneophores. There was a danger of losing part of the genetic material or violating its structure. As a result, a cavity was formed in the cell, separated by a membrane from the cytoplasm. Gradually, it transformed into a core. So the first eukaryotic cells appeared.
Organelles such as mitochondria and flagella most likely also arose during phagocytosis. The precursors of modern cells, absorbing food, acquired symbionts, friendly microorganisms.Using nutrients that enter the cytoplasm, they began to exercise the functions of regulating various intracellular processes. According to the concept of symbiogenesis, in this way the already mentioned mitochondria and flagella appeared in the cell. Many modern studies confirm the validity of the hypothesis.
Alternatives
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To summarize all of the above, it becomes clear that the origin of the Earth and life on it today are still open questions. Modern scholars, of course, are much closer to unraveling all the secrets of our planet than thinkers of Antiquity or the Middle Ages. However, much more needs to be clarified. Various hypotheses of the origin of the Earth succeeded each other at those moments when new information was discovered that did not fit into the old picture. It is possible that this could happen in the not too distant future, and then new theories will replace the established theories.