Chemical evolution: stages and essence

In the process of the transformation of chemistry into science, the so-called chemical evolution was taking place, and the turning point of this revolutionary process came after the creation in 1777 of the French natural scientist Lavoisier of the theory of combustion with a description of the role of oxygen. At the same time, the revision of all the basic concepts and main principles of chemistry began, the terminology and nomenclature of substances changed.

Elementary course

The year 1789 marked the release of the textbook Lavoisier, immediately became the main tool for theorists and practitioners of the born science. In the "Elementary course of chemistry" was already the first in the world list - a table of simple bodies, which listed the known chemical elements. At the heart of this volume of Lavoisier lay the oxygen combustion theory, through which chemical evolution was directed along a completely new path. The most important thing in determining the element is experience, it was he who selected the scientist as the main criterion, and anything that is not confirmed by experience, for example, an atomic or molecular structure, Lavoisier did not consider.

Chemical evolution has gone by the laws formulated by it - about the preservation of the mass, the nature of the properties of the compounds, their differences in the elemental composition. It was then that chemistry took the form of science as an independent, studying the composition of bodies by experimental means. Chemical evolution could not do without the rationalization of the object, and thus, mankind finally abandoned the alchemical past, because the ideas about the nature of matter and its properties changed radically and very quickly. And the impetus for this process was the research of Lavoisier. Now even schoolchildren know that the stages of chemical evolution (or prebiotic evolution) need to be considered from the time that preceded the emergence of life on Earth. In the eighteenth century, no one had such ideas about the world yet.

A life

The chemical evolution of the Earth began on an absolutely lifeless planet, when organic substances gradually began to emerge from inorganic molecules, which were influenced in a special way by energy and selection factors. The processes of self-organization that are characteristic of even relatively complex systems have unfolded. So, on the Earth there was a carbon. Rather, carbon-containing molecules first appeared, which are of fundamental importance not only for the emergence, but also for the further development of any living matter.

We still do not know what is the essence of chemical evolution at the early stages of life development. 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 existence of living matter, and our protein origin is not the only "way out". Here, a unique combination of polymerization qualities of carbon with the depolarizing properties of the aqueous medium in the liquid phase was realized. These conditions were sufficient to start the chemical evolution of life, and also necessary for the development of all the variety of life forms known to us.

Start the process

Mankind knows not even everything about its own cradle. Especially about where and when the stages of chemical evolution on Earth began. We can only assume this. Here, in the first place, absolutely any time is 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 already in the second generation acquired their own planetary systems, where the necessary heavy elements were already sufficient. 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 life was born

Where it could originate is also an open question. When creating many fairly likely conditions, the launch of a chemical ecology could occur in virtually any environment. This is the depths 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 attacking living matter on lifelessness, and this is confirmed by the organic substances found there - alcohols and sugars, aldehydes, amino acids of glycine and many others, that can serve as the starting material for the emergence of life through the chemical evolution that has begun.

Theory

The ancient Earth keeps its secrets, and mankind does not yet have reliable information about the geochemical conditions of its existence before the appearance of life. Geological studies can not satisfy all emerging issues, and therefore astronomy is widely used for study. So the theory of chemical evolution is built. Today's Venusian or Martian conditions are regarded as analogous to the Earth at certain stages of chemical evolution.

Experiments are put on models, and thus all the basic data known to us are obtained. For example, by simulating various chemical compositions and climatic conditions in the atmosphere, hydrosphere, lithosphere, complex organic molecules were obtained. The acquisition of new data by experimental means always enriches the theory under construction. Thus, there have been many hypotheses about specific mechanisms and directly driving forces of the chemical evolution that has taken place.

Research in Russia

Life on Earth was formed due to abiogenesis, that is, the birth of organic compounds whose existence is inherent in living nature outside any organism and without the slightest involvement of enzymes. This is the very first stage when the living one appears from the lifeless.

According to the assumption of Academician Oparin in the twenties of the twentieth century, solutions of high-molecular 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 coacervates or coacervate drops.

Abroad

The first abiogenic synthesis, carried out under the conditions of primitive 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 that follow one another, where the product of the previous one becomes the catalyst for the next.

Only in 2008, American biologists created the first "protocell", which through the membrane of fatty acids and lipids was able to obtain nucleotide monophosphates from the environment. These imidazole-activated "bricks" are absolutely necessary for DNA synthesis. And in 2011 in Japan, vesicles were created with elements of DNA under the cationic shell, which were capable of dividing, since there was a poly-dimensional chain reaction replicating the DNA.

Main hypotheses

The chemical evolution of life on Earth in hypotheses explains the following fundamental points.

1. The need for the appearance on the Earth or in the Cosmos of the conditions under which autocatalytic synthesis of hu- trogen-containing molecules occurs, and the synthesis must have large volumes and a considerable variety sufficient for the beginning of the process of chemical evolution.
2. The emergence of pro-cellular structures emerging from the molecules described above. These stable closed aggregates are isolated from the environment, the metabolism and energies in them pass selectively. So there are pro-cellular structures.
3. In the resulting aggregates, there is the ability for independent development - self-replication and self-change of all information chemical systems. So there are elementary units of the hereditary code.
4. The next stage is the appearance of interdependence between enzyme functions and the properties of proteins with RNA and DNA as carriers of information. So there is actually a heredity code, which is necessary for biological evolution.

Discoveries

As it was said above, Oparin opened coacervates in the twenties of the last century. Further Stanley Miller and Harold Urey in 1953 described the occurrence in the simulating ancient atmosphere of simple biomolecules and the process of their occurrence. Next, Sydney Fox told the world about the microspheres of the protenoids. In 1981, T. Cecu and S. Altman succeeded in observing autocatalytic division of RNA, as ribozymes are able to combine information and catalysis in a molecule, "cutting" themselves out of the chain and connecting the remaining "ends."

In 1986, W. Gilbert of Cambridge developed the idea of the "World of RNAs," while Günter von Kidrowski from Germany presented the first self-replicating DNA-based system, which was a major contribution to understanding the self-replicating systems and the functions of their growth. Science quickly moved forward in this direction: Manfred Eigen discovered the hypercycle, the evolution of ensembles of RNA molecules, and Julius Rebecque created the first artificial molecule that self-replicates in chloroform.

Space and Earth

At NASA's Space Flight Center, John Corlis studied the process of supplying energy and chemicals from the thermal springs of the seas, which make the chemical evolution independent of the space environment, and today they are for the original archeobacteria a permanent habitat. In the world of iron sulfides, a number of hypotheses of Gunther Wachtershauser appeared.

He described the first self-replicating structures with the exchange of substances that appeared on the surface of pyrite (iron sulphide), which gave the energy necessary for the metabolism. Under selection conditions, growing and decaying pyrite crystals can grow and multiply, creating different populations. Clay minerals were also densely studied for the appearance of organic molecules. Nevertheless, the unified model of chemical evolution does not exist yet, since the basic principles of the movement of this process are not yet open.