Origin of Life on Earth
Life originated on Earth about 3.5 billion years ago. This was preceded by a very long abiogenic (abiotic) molecular evolution. Modern science has completely denied all the myths about the sudden “miraculous” appearance of life. Insolvency were also theories about the drift of life from space. Now we can imagine the conditions under which the world became real origin of life. The most widely accepted hypothesis of the origin of life received by J. Alexander Oparin – JB S. Haldane (1924 – 1927). According to this hypothesis, now augmented, complicated process of the origin of life is as follows.
On a hot (up to 1000 ° C) the planet, which was the Earth, all the elements were in the atomic state and cooled gradually redistributed accordingly density: the most difficult – inside, the lightest (nitrogen, hydrogen, carbon) – on the surface. Thus was formed the early atmosphere, made up of gases. Its composition was no free oxygen as it combines with metals and other oxidizable elements. Free hydrogen and gaseous compounds of nitrogen, carbon and oxygen (water vapors) a reducing nature of the medium, which was one of the preconditions for the formation of organic molecules by non-biological. Further cooling resulted in the condensation of water vapor; on the surface of the Earth began to dash down hot showers, forming a huge expanse of water. In the water were dissolved ammonia (NH3), carbon dioxide (CO2), methane (CH4), hydrogen cyanide (HCN). In the atmosphere under the action of ultraviolet rays of the sun and lightning going formation of more complex organic compounds, which with the rains also fell into the water. Among them – organic acids (acetic, formic, lactic, etc.), Adenozinfosfatnye compound (AMP, ADP, ATP), and others. Since frequent volcanic eruptions, including underwater, imposed onto the surface (and is now taken out) as complex compound as various amino acids (blocked abiotic synthesis is performed at a temperature of about 1000 ° C), nitrogenous bases, amino sugars and other non-organic substances. Carbides (metal compounds with carbon), also erupted in large quantities in hot water formed hydrocarbons. The reducing nature of the Earth’s atmosphere, volcanic activity, lightning, strong ultraviolet radiation, is not filtered by the ozone-screen, high temperature – these are the conditions that ensure abiogenic occurrence of organic compounds and triggered chemical evolution, which led eventually to the emergence of living organisms. Currently, the experimental confirmation of abiotic synthesis even substances such as proteins. The warm waters of the ocean were the primary favorable environment for chemical reactions between dissolved are organic and inorganic substances, low molecular weight organic matter is converted into more complex high molecular weight. Over millions of years, they arose and destroyed countless varieties of organic compounds. There was a gradual accumulation of the waters primary ocean.
The next stage in the development of organic substances – education coacervate drops. In aqueous solution, the organic molecules are always surrounded by a polarized water shell. Its thickness is dependent on the charge of the molecule, the salt concentration of the surrounding solution, temperature and other factors. Molecules, surrounded by such shells can be combined to form coacervates – multimolecular group with a single shell that is not mixed with the surrounding solution. Coacervate droplet formation are high, including protein and polynucleotide, segregate from the solution as colloidal particles. Research Oparin showed that coacervate drops are capable of adsorbing (absorbing) from the surrounding solution individual substances and increase in size. The coacervates is simple fusion and decay of substances whose products stood out. These processes can be compared with the processes of nutrition, growth, selection. Thus, the absorption capacity inherent coacervates was apparently, the initial step in their metabolism. There was one of the most significant signs of life – metabolism.
The coacervate droplets containing the polynucleotide chain during adsorption occurred mononucleotides non-enzymatic synthesis of complementary polynucleotides, t. E. The matrix synthesis, so characteristic of living systems. It formed the ability to reproduce.
Height coacervate drops due to the absorption of substances from outside led to disparities between the mass of the drop and cohesive forces between its molecules. The drop breaks up into several smaller ones. This process has become a necessary precondition for the emergence of breeding. However, in the modern sense of reproduction – is the process by which organisms reproduce their own kind. With the disintegration of the coacervate “daughter” drops could be very different in chemical composition. Many of them broke up on and died, some were growing again. As part of the coacervate drops there are all new and new combinations of materials.
The greatest chance of saving had drops containing a protein capable on their chemical nature to the enzymatic activity, and polynucleotides. Enzyme protein involved not only in the metabolism, but also in the replication of nucleic acids. Keeping in nucleic acids capable of replication, information about the “successful” combinations of amino acids provided the stability of the composition of proteins in the decay drops. Thus, there was a process of self-reproduction – a necessary feature of the living. Complete the last stage of the chemical evolution of matter, any living system. The development of living systems proceeded as a result of biological evolution. When replication of polynucleotide molecules in some cases there were “mistakes” – mutations: a new molecule is not quite exact copy the source. Subsequently, this modified molecule is copied. The frequency of mutation increased dramatically under the influence of radiation, especially ionizing. Since the inception of the simplest organisms caught in the action of natural selection, which ensures their adaptability to the conditions of existence. Accidentally acquired as a result of hereditary changes useful signs were fixed selection. Apparently, that’s of primary coacervates formed cells: outer membrane formed with the property of selective permeability, cytoplasm and nucleus; It was the evolution of biochemical processes.
The primary organisms are used to supply ready-made organic compounds, ie. E. Were anaerobic heterotrophs. In terms of increasing their numbers with decreasing reserves of organic matter in the primary ocean some organisms appeared entrenched capacity for independent synthesis of organic compounds from inorganic by the energy of simple oxidation and reduction reactions. There was chemosynthesis. Chemosynthetic bacteria were the first autotrophic organisms. The primary organisms gradually reduced the original reserves of hydrogen, ammonia, methane, hydrogen sulfide. For example, hydrogen sulfide, sulfur bacteria oxidized volcanic origin, and hydrogen – atmospheric molecular hydrogen.
The next important stage of biological evolution – the creation of pigment systems for light energy – the emergence of photosynthesis. The first organisms that use light as an energy source for the synthesis of organic substances were bacteria (such as purple and green sulfur bacteria) and cyan (blue-green). The latter was used as a hydrogen source water, and began to escape into the atmosphere free of oxygen, which was a prerequisite for the evolution of occurrence during aerobic respiration, which is almost 20 times more efficient anaerobic anoxic oxidation. Aerobic oxidation (an important step in the evolution) is gradually replacing anaerobic uneconomical.
According to geological data, it has 2.7 billion. Years in the atmosphere in small amounts had free oxygen. With the accumulation of oxygen in the upper atmosphere, part of it was transformed into ozone that can rapidly absorb ultraviolet and ionizing radiation of the sun – has formed “ozone shield”. Life, which was initially available only in the ocean, under the protection of water left on the land and spread over the entire surface of the Earth.
Life on Earth arose abiogenically. It is currently non-biological pathway of living organisms, ie. E. Spontaneous generation of life? No. Firstly, the planet no conditions (temperature, atmosphere, and so on. D.) Required for the synthesis of organic substances abiogenous. Second, it prevents an abundance of heterotrophic beings, ready to use immediately for food, any organic compounds. In the present conditions of our planet all organisms, even the most primitive, there are only biologically, ie. E. In the process of reproduction of their kind.
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