In the process of transforming chemistry into science, the so-called chemical evolution took place, and the turning point of this revolutionary process came after the creation of the theory of combustion with the description of the role of oxygen by the French natural scientist Lavoisier. Then the revision of all fundamental concepts and the main principles of chemistry began, the terminology and nomenclature of substances changed.
Elementary course
The year 1789 was marked by the release of the Lavoisier textbook, which immediately became the main manual for theorists and practitioners of born science. The Elementary Chemistry Course already had the first list in the world - a table of simple bodies listing known chemical elements. This folio of Lavoisier was based on precisely the oxygen theory of combustion, through which chemical evolution was directed in an entirely new way. The most important thing in the definition of an element is experience, it was precisely the scientist who chose the main criterion, and Lavoisier did not consider everything that was not confirmed experimentally, for example, atomic or molecular structure .
Chemical evolution went the way he formulated laws - on the conservation of mass, on the nature of the properties of compounds, on their differences in elemental composition. It was then that chemistry took the form of independent science, studying the composition of bodies experimentally. Chemical evolution could not do without rationalization of the subject, and thus, mankind finally abandoned the alchemical past, since ideas about the nature of matter and its properties changed radically and very quickly. And the impetus for this process was the study of Lavoisier. Now even schoolchildren know that the stages of chemical evolution (or prebiotic evolution) must be considered from the times that preceded the emergence of life on Earth. In the eighteenth century, no one had such ideas about the world.
A life
The chemical evolution of the Earth began on an absolutely lifeless planet, when organic substances gradually began to arise from inorganic molecules, which were specially influenced by energy and selection factors. Self-organization processes unfolded, which are characteristic of even relatively complex systems. So, carbon appeared on Earth. Rather, carbon-containing molecules first appeared, which are of fundamental importance not only for the occurrence, but also for the further development of all living matter.
We still do not know what the essence of chemical evolution is in the early stages of the development of life. Known about the chemistry of any substance limits the evolutionary process to the boundaries of the water-carbon postulate. Perhaps in the Universe there are variants of a different way of living matter existence , and our protein origin is not the only "appearance". Here a unique combination of the polymerization qualities of carbon with the depolarizing properties of the aqueous medium in the liquid phase took place. These conditions turned out to be sufficient for the chemical evolution of life to begin, as well as necessary for the development of the whole variety of life forms known to us.
Process start
Humanity, even about its own cradle, is far from everything. Especially about where and when the stages of chemical evolution on Earth began. We can only speculate about this. Here, firstly, absolutely any terms are possible.
When the second cycle of star formation ended, when the products of the explosion of supernovae were condensed , which gave the interstellar space elements called heavy, in which the mass exceeds twenty-six. When the stars in the second generation found their own planetary systems, where there were already enough necessary heavy elements. The essence of chemical evolution could be realized at any moment after the Big Bang in the interval from half a billion to one and a half billion years.
Where did life begin?
Where it could have originated is also an open question. With the creation of many fairly probable conditions, the launch of chemical ecolution could occur in almost any environment. This is the bowels of the planets, and the depths of the oceans, and the surface, even protoplanetary formations are suitable.
Moreover, clouds of interstellar gas can also serve as a springboard for the attack of living matter on lifelessness, and this is confirmed by the organic substances found there - alcohols and sugars, aldehydes, glycine amino acids, and much more that can serve as the starting material for the emergence of life through the beginning of chemical evolution.
Theory
The Ancient Earth keeps its secrets, and humanity does not yet have reliable information about the geochemical conditions of its existence before the emergence of life. Geological research cannot satisfy all the questions that arise, and therefore astronomy is widely used to study. So the theory of chemical evolution is built. Today's Venusian or Martian conditions are regarded as similar to the Earth at certain stages of chemical evolution.
Experiments are performed on models, and in this way all the basic data known to us are obtained. For example, by simulating a variety of chemical compositions and climatic conditions in the atmosphere, hydrosphere, lithosphere, complex organic molecules were obtained. Getting new data by experiment always enriches the theory under construction. Thus, hypotheses regarding specific mechanisms and directly driving forces of the completed chemical evolution have been put forward in a multitude.
Research in Russia
Life on Earth was formed due to abiogenesis, that is, the birth of organic compounds, the presence of which is characteristic of living nature outside any organism and without the slightest involvement of enzymes. This is the very first stage when the living appears from the inanimate.
According to the assumption of academician Oparin in the twenties of the twentieth century, solutions of macromolecular compounds are able to form certain zones where their concentration is increased, and separation from the external environment does not prevent them from exchanging with it. These zones are called coacervate or coacervate drops.
Abroad
The first abiogenic synthesis, carried out in the conditions of the primeval Earth, was carried out in 1953 by Stanley Miller, synthesizing amino acids with other organic substances. Subsequently, the theory of hypercycles appeared, which explains the manifestations of life in the process of chemical evolution by the presence of complexes of catalytic reactions following each other, where the product of the previous one becomes the catalyst for the next.
Only in 2008, American biologists created the first "protocell", which, through a shell of fatty acids and lipids, was able to receive nucleotide monophosphates from the environment. These imidazole-activated “bricks” are absolutely essential for DNA synthesis. And in 2011, Japan created vesicles with DNA elements under the cationic shell, which were capable of division, because there was a poly-dimensional chain reaction that replicates DNA.
The main hypotheses
The chemical evolution of life on Earth in hypotheses explains the following fundamental points.
- The need for the appearance on Earth or in space of the conditions under which the autocatalytic synthesis of carbon-containing molecules occurs, and the synthesis must have large volumes and significant diversity, sufficient to start the process of chemical evolution.
- The emergence of protocellular structures emerging from the molecules described above. These stable closed units are isolated from the environment, the metabolism and energy in them passes selectively. This is how protocellular structures arise.
- In the aggregates formed, the ability for independent development appears - self-replication and self-change of all information chemical systems. So there are elementary units of the hereditary code.
- The next stage is the emergence of the interdependence between the functions of enzymes and the properties of proteins with RNA and DNA as information carriers. So the actual code of heredity arises, which is necessary for biological evolution.
Discoveries
As mentioned above, Alexander Oparin discovered coacervates in the twenties of the last century. Further, Stanley Miller and Harold Urey in 1953 described the appearance of simple biomolecules in the simulating ancient atmosphere and the process of their occurrence. Then Sydney Fox told the world about microspheres from protenoids. In 1981, T. Chek and S. Altman managed to observe the autocatalytic fission of RNA, as ribozymes are able to combine information and catalysis in a molecule, “cutting” themselves from the chain and connecting the remaining “ends”.
In 1986, W. Gilbert from Cambridge developed the idea of the “RNA World”, and Gunther von Kidrowski from Germany at the same time presented the first self-replicating system based on DNA, which was the most important contribution to the understanding of self-replicating systems and their growth functions. Science quickly advanced in this direction: Manfred Eigen discovered a hypercycle, the evolution of ensembles of RNA molecules, and Julius Rebeck created the first artificial molecule that self-replicates in chloroform.
Space and Earth
At the NASA Space Flight Center, John Corlis studied the process of delivering energy and chemicals from the thermal sources of the seas, which make the chemical evolution independent of the space environment, and today they are a permanent habitat for the original archaeobacteria. A number of Gunther Wahtershuiser hypotheses have appeared in the world of iron sulfides.
He described the first self-replicating metabolism structures that appeared on the surface of pyrite (iron sulfide), which gave the energy necessary for metabolism. Under selection conditions, growing and decaying pyrite crystals can grow and multiply, creating various populations. Clay minerals have also been closely studied for the appearance of organic molecules. Nevertheless, a unified model of chemical evolution does not yet exist, since the basic principles of the movement of this process are not yet open.