Life is the greatest miracle that exists on our planet. Problems of its study now occupy not only biologists, but also physicists, mathematicians, philosophers and other scientists. Of course, the most difficult mystery is the very origin of life on Earth.
Until now, researchers are arguing about how it happened. Strange as it may seem, a significant contribution to the study of this phenomenon has been made by philosophy: this science allows us to draw the right conclusions, generalizing huge volumes of information. What versions are guided today by scientists around the world? Here are some theories of the origin of life on Earth:
- The concept of spontaneous generation.
- Creationism, or the theory of divine creation.
- The principle of stationary state.
- Panspermia, whose supporters claim the natural "productivity" of any planet where there are suitable conditions. In particular, this idea was developed in due time by well-known academician Vernadsky.
- Biochemical evolution according to AI Oparin.
Let's consider all these theories of the origin of life on Earth in more detail.
Materialism and idealism
Even in the Middle Ages and earlier, in the Arab world, some scientists, even with a risk to their own lives, assumed that the world could be created as a result of some natural processes, without the participation of the divine essence. These were the first materialists. Accordingly, all the other points of view that provided for the Divine intervention in the creation of all things were idealistic. Accordingly, it is quite possible to consider the origin of life on Earth from these two positions.
Creationists claim that life could only be created by God, while materialists promote the theory of the appearance of the first organic compounds and life from inorganic substances. Their version is based on the complexity or impossibility of understanding those processes, the result of which was life in its modern form. It is interesting, but the modern Church supports this hypothesis only partially. From the point of view of the most friendly to scientists figures, the basic intention of the Creator is impossible to understand and it is really impossible, but we can determine the phenomena and processes through which life has arisen. However, from a truly scientific approach it is still very far away.
At the present time the point of view of materialists prevails. However, they did not always put forth modern theories of the origin of life. Thus, the hypothesis was initially popular that the origin and evolution of life on Earth occurred spontaneously, and supporters of this phenomenon met in the beginning of the 19th century.
Supporters of this concept argued that there are certain laws of a natural nature that cause the possibility of an arbitrary transition of inorganic compounds into organic compounds with subsequent arbitrary formation of life. This also applies to the theory of the creation of a "homunculus," an artificial person. In general spontaneous generation of life on Earth is still considered by some "experts" seriously ... Well at least, what they say about bacteria and viruses.
Of course, the error of this approach was subsequently proved, but it played an important role, giving a huge amount of valuable empirical material. Note that the final rejection of the version of an independent birth of life occurred only in the middle of the XIX century. In principle, the impossibility of such a process was proved by Louis Pasteur. For this, the scientist even received a considerable award from the French Academy of Sciences. Soon, the main theories of the origin of life on Earth are put forward, which we will describe below.
Theory of Academician Oparin
Modern ideas about the origin of life on Earth are based on a theory that was put forward by the Russian researcher, Academician Oparin, back in 1924. He refuted the Redi principle, which spoke of the possibility of only a biogenic synthesis of organic substances, pointing out that this concept is valid only for the current state of affairs. The scientist pointed out that at the very beginning of its existence our planet was a giant rocky ball, on which there was basically no organic matter.
Oparin's hypothesis was that the birth of life on the planet Earth is a long biochemical process, the raw materials for which are ordinary compounds that can occur on any planet. The academician suggested that the transition of these substances to more complex ones was possible under the influence of extremely strong physical and chemical factors. Oparin first put forward the hypothesis of the continuous transformation and interaction of organic and inorganic compounds. He called it "biochemical evolution". Below are the main stages of the birth of life on Earth by Oparin.
Stage of chemical evolution
About four billion years ago, when our planet was a huge and lifeless stone in the depths of the cosmos, the process of nonbiological synthesis of carbon compounds was already on its surface. During this period volcanoes threw out a titanic quantity of lava and hot gases. Cooling down in the primary atmosphere, the gases turned into clouds, from which the torrential rains were continually pouring. All these processes have been going on for millions of years. But, allow me, when did the beginning of life on Earth begin?
At the same time, showers gave rise to huge primary oceans, the waters of which were extremely saturated with salts. The first organic compounds that formed in the atmosphere under the influence of strong electric discharges and UV irradiation also fell there. Gradually, their concentration increased until the sea turned into a sort of "broth", saturated with peptides. But what happened next and how did the first cells originate from this "soup"?
Formation of protein compounds, fats and carbohydrates
And only at the second stage in the "broth" there are true proteins and other compounds from which life is built. Conditions on Earth softened, carbohydrates, proteins and fats appeared, the first biopolymers, nucleotides. So it was the formation of coacervate drops, which were the prototype of real cells. Roughly speaking, the so-called drops from proteins, fats, carbohydrates (as in the soup). These formations could absorb, absorb those substances that were dissolved in the waters of the primary oceans. At the same time, there was a kind of evolution, the result of which were drops that have increased stability and stability to environmental influences.
The appearance of the first cells
Actually, at the third stage this amorphous formation turned into something more "meaningful". That is, in a living cell, capable of a process of self-reproduction. The natural selection of drops, about which we have already spoken above, became more and more rigid. The first "advanced" coacervates already had a primitive, but a metabolism. Scientists suggest that the drop, reaching a certain size, disintegrated into smaller formations that possessed all the features of the maternal "cell".
Gradually a layer of lipids appeared around the nucleus of the coacervate, which gave rise to a full-fledged cell membrane. Thus, primary cells, archeklets, were formed. It is this moment with full right to that can be regarded as the birth of life on Earth.
Is non-biological synthesis organic?
As for the hypothesis of the birth of life on Earth from Oparin ... Many immediately have the question: "How realistic is the formation in natural conditions of organics from inorganics?" Such thoughts were visited by many researchers!
In 1953, the American scientist Miller modeled the primary atmosphere of the Earth, with its incredible temperatures and electrical discharges. In this medium, simple inorganic compounds were placed. As a result, acetic and formic acids, other organic compounds, were formed there. This is how the origin of life on Earth took place. In short, this process can characterize the philosophical law of "The transition of quantity to quality." Simply put, with the accumulation of a certain amount of proteins and other substances in the primary ocean, these compounds acquire other properties and the capacity for self-organization.
Strengths and weaknesses of Oparin's theory
The concept we have examined has not only strong but also weak points. The strength of the theory is its logic and experimental confirmation of the abiotic synthesis of organic compounds. In principle, this could be the origin and development of life on Earth. The great weakness is the fact that no one can yet explain how coacervates could be reborn into a complex biological structure. Even supporters of the theory recognize that the transition from a protein-fat drop to a full-fledged cell is highly questionable. Probably, we are missing something, not taking into account factors unknown to us. Currently, all scientists recognize that there was some sharp jump, as a result of which self-organization of the substance became possible. How could this happen? While it is unclear ... What other basic theories of the origin of life on Earth exist?
Theory of panspermia and steady state
As we have already said, in due time this version was fervently supported and "promoted" by the famous academician Vernadsky. In general, the theory of panspermia can not be discussed in isolation from the concept of a stationary state, since they consider the principle of the origin of life from the same point of view. It should be noted that this concept was first proposed by the German Richter at the end of the 19th century. In 1907 he was supported by the Swedish researcher Arrhenius.
Scientists who adhere to this concept believe that in the Universe life simply existed and will always exist. From the planet to the planet, it is transferred with the help of comets and meteorites, which play the role of peculiar "seeds". The disadvantage of this theory is that the Universe itself is supposed to have formed about 15-25 billion years ago. On "Eternity" it does not seem like it. Taking into account the fact that potentially suitable for the formation of life of planets is many times less than the usual rocky planetoids, it is quite natural to consider the emergence of the question: "When and where was life formed and how did it spread with such speed over the universe, taking into account unrealistic distances?"
It should be remembered that the age of our planet is not more than 5 billion years. Comets and asteroids fly much slower than the speed of light, so they might simply not have enough time to put the "seeds" of life on Earth. Supporters of panspermia suggest that certain seeds (spores of microorganisms, for example) are transferred "on light beams" with the appropriate speed ... Here only decades of spacecraft work allowed to prove that in space there are quite a few free particles. The probability of such a method of spreading living organisms is too small.
Some researchers today suggest that on any planet that is suitable for life, eventually protein bodies can form, but the mechanism of this process is unknown to us. Other scientists say that in the universe, perhaps, there are some "cradles", planets on which life can be formed. Sounds, of course, like some kind of science fiction ... However, how to know. In recent years, both in Russia and abroad, a theory gradually began to take shape, the provisions of which refer to the information originally encoded in the atoms of information ...
Allegedly, these data give the same impetus that leads to the transformation of the simplest coacervates into archets. Logically, this is the same theory of spontaneous generation of life on Earth! In general, the concept of panspermia is difficult to consider a completed scientific thesis. Its supporters can only say that life was brought to Earth from other planets. But how did it form there? There is no answer to this.
A gift from Mars?
Today it is for certain that there really was water on the Red Planet and there were all conditions favorable to the development of protein life. Data, which confirm this, were obtained due to the work on the surface of just two descent vehicles: Spirit and Curiosity. But scientists are still arguing heatedly: was there life there? The fact is that the information received from the same rovers indicates the short-term (in geological aspect) the existence of water on this planet. How high is the probability that there in principle have developed full-fledged protein organisms? Again, there is no answer to this question. Again, even if life came to our planet from Mars, it does not explain the process of its development there (about which we already wrote).
So, we have considered the basic concepts of the origin of life on Earth. Which of them are absolutely correct, is unknown. The problem is also that there is not yet one experimentally confirmed test that could confirm or disprove at least Oparin's concept, not to mention other theses. Yes, we can synthesize protein without special problems, but we can not get a protein life. So the work of scientists is stored for many decades to come.
There is another problem. The fact is that we are intensively looking for a life based on carbon, and we are trying to understand exactly how it originated. And what if the concept of life is much broader? What if it is based on silicon? In principle, this point of view does not contradict the provisions of chemistry and biology. So on the way of searching for answers we are met with more and more new questions. At present, scientists have put forward several basic theses, guided by which people are searching for potentially inhabited planets. Here they are:
- The planet must go in the so-called "comfort zone" around the star: there should be neither too hot nor too cold on its surface. In principle, at least one or two planets in each stellar system respond to this demand (Earth and Mars, in particular).
- The mass of such a body should be medium (within one and a half times the size of the Earth). Too large planets or have an unrealistically high gravity, or are gas giants.
- A more or less highly organized life can exist only near enough old stars (no less than three or four billion years).
- The star should not seriously change its parameters. To search for life near white dwarfs or red giants is useless: if it was there, it had long since died because of extremely unfavorable environmental conditions.
- It is desirable that the stellar system be single. In principle, modern researchers object to this thesis. It is possible that a dual system with two stars located at opposite ends may contain even more potentially inhabited planets. Moreover, today more and more talk about the fact that somewhere on the outskirts of the solar system there is a gas-dust cloud, the forerunner of the never-born second Sun.
So, what can we say in conclusion? First, we do not have enough data on exact environmental conditions on the newly emerged Earth. To obtain this information, ideally, one should observe the development of the planet, which is analogous to our other indicators. In addition, researchers are still at a loss to say which factors stimulate the transition of arhekapel coacervates to full cells. Perhaps, further in-depth studies of the genome of living beings will give some answers.