According to one hypothesis, primitive precellular life arose over four billion years ago on land among volcanoes and fumaroles, which provided all the necessary chemistry for its preservation and nutrition. This could have happened both on Earth and on Mars.
A living cell is a very complex organism that combines many elements, mechanisms and processes. How it was formed is unknown. Some scientists are trying to synthesize a cell as a whole, others go from simple to complex, figuring out how its constituent parts were formed separately and then evolved over billions of years.
For a long time, it was believed that life originated in the oceans, but recently this point of view has been criticized. Although water is part of the cell, it is harmful for the spontaneous synthesis of biomolecules. In addition, there is no evidence that seas and oceans existed on the surface of the planet more than four billion years ago, when, presumably, the process of the origin of life began.
Chemistry of the RNA World
The role of proto-life is claimed by molecules of ribonucleic acid, RNA. They are able to store information, reproduce, synthesize proteins and independently perform many different functions, which in a modern cell have taken over DNA, enzymes and other biological molecules.
RNA molecules are made up of alternating nucleotides linked by oxygen bridges. Scientists have long tried to recreate the links of the polymer chain of this complex molecule, but the breakthrough came only in 2009, when British researchers Matthew Powner and John Sutherland published the results of experiments on the synthesis of two RNA nucleotides - cytosine and uracil. They were obtained in laboratory conditions from simple organic matter and phosphate after ultraviolet irradiation.
“They synthesized two natural nucleotides entirely. It was a tremendous breakthrough, - says RIA Novosti Armen Mulkidzhanyan, Doctor of Biological Sciences, employee of the A. N. Belozersky Research Institute of Physical and Chemical Biology, Lomonosov Moscow State University, employee of the Physics Department of Osnabruck University (Germany).
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The nucleotide consists of a nitrogenous base, sugar (ribose) and phosphate groups, when attached to which energy is stored. Alexander Butlerov showed how to obtain mixtures of complex sugars from organic matter in 1859. A century and a half later, American chemist Steven Benner found out that in order for this reaction to selectively form ribose, molybdenum oxide is needed as a catalyst. In addition, to stabilize the resulting sugars, a lot of borates - boric acid salts are needed. Benner theorized that such chemical conditions could exist somewhere in deserts, such as the dry, basalt heights of Mars.
“Indeed, early Mars and Earth were very similar. Mars may have had an even more oxidized atmosphere than ancient Earth, and borate deposits have been found there, suggesting long-standing geothermal activity. Half of the territory of Mars is composed of rocks older than four billion years, so it makes sense to look for traces of life there. Due to plate tectonics, rocks of this age have not survived on Earth,”explains Mulkidzhanyan.
Solfatara volcano, Phlegraean Fields, Italy / CC BY 2.0 / NH53 / Solfatara, Phlegraean Fields.
There is no life without light
Cell energy specialist Armen Mulkidzhanyan has long been dealing with the problem of the origin of life, which has venerable traditions in Soviet and Russian science. Suffice it to say that Academician Alexander Oparin is considered the founding father of this scientific direction all over the world.
Mulkidzhanyan and colleagues suggested that ultraviolet light could be a key factor in the selection of the first biomolecules. The ancient atmosphere contained neither oxygen nor ozone. It retained those biomolecules that could, at first, simply be heated by the sun's rays without decaying. This is evidenced by the fact that all natural nitrogenous bases of RNA have this property. But living protoorganisms would hardly have withstood the harsh cosmic radiation, the biologist believes. This means that there can be no question of their delivery by meteorites from Mars to Earth.
Geothermal fields that form around volcanoes are suitable for the origin of life. Instead of water, as in geysers, steam is escaping from the hot springs, saturated with all the necessary components. It contains carbon dioxide, hydrogen, ammonia, sulfides, phosphates, molybdenum, borates, potassium - and there is more of it than sodium. Potassium also predominates in the cells of all organisms, because otherwise protein biosynthesis is impossible. As Mulkidzhanyan and colleagues have shown, potassium is essential for the functioning of the most ancient proteins. Bioinformatics Evgeny Kunin managed to calculate them in 2000 during the reconstruction of the common ancestor of all cellular organisms - LUCA (Last Universal Cellular Ancestor).
The proteins that code for the LUCA genes also use zinc ions as catalysts or building blocks.
“Zinc sulphides can form all bacteria. Interestingly, crystals of zinc sulfide and a similar cadmium sulfide are capable of reducing carbon dioxide under ultraviolet light to organic, potentially “edible” molecules. Therefore, the first living organisms could cover themselves with crystals of these minerals in order to protect themselves from ultraviolet radiation and get food,”the scientist explains.
Zinc is volatile, slowly crystallizes and precipitates, unlike iron and copper, at the periphery of geothermal fields, where it is not hot.
“On the cool periphery of such fields, 'rings of life' could have formed around hot thermal springs,” the researcher concludes.
Geothermal fields still exist on Earth - unlike Mars, whose bowels have cooled down. Armen Mulkidzhanyan, together with geochemist Andrey Bychkov from Lomonosov Moscow State University, studied the chemical conditions of fumaroles near the Mutnovsky volcano in Kamchatka. Similar conditions are observed in Yellowstone National Park in the United States, in the Lardarello geothermal fields in Italy and Matsukawa in Japan.
Recently, traces of a 3.5 billion-year-old geothermal field were discovered in the Pilbara region of Australia, the same place where the oldest traces of living communities on Earth were found.
Tatiana Pichugina