Life originated on the Earth more than 3.5 billion years ago. However, the scientists are still disputing over the possible sources of the life origin. The matter is that life on our planet evolved from the molecular level to the level of bacteria organisms within 0.5 – 1 billion years, this period being very short for such an important evolutionary step. The researchers are still racking the brains over this mystery. One of the popular hypothesis asserts that some germs of life have been brought to the Earth from space. But what exactly could have been brought from space and how could the germs have originated in space?
E.A. Kuzicheva and N.B.Gontareva, research assistants from the Institute of Cytology, Russian Academy of Sciences, have confirmed a possibility of abiogenous synthesis of complex organic compounds (monomeric units of nucleic acids) on the surface of comets, asteroids, meteorites and space dust particles in the outer space. Therefore, it is possible that the above monomeric units of nucleic acids could have got to the Earth and thus could have significantly reduced the time period of the evolution process. On the surface of space bodies the scientists have found all kinds of various organic molecules (amino acids, organic acids, sugars etc.) and the components required for their synthesis. Obviously, it is there that organic substances are being synthesised, but the researchers can not be sure of this fact, until the experiments confirm their assumptions. The scientists from St. Petersburg reproduced synthesis of one of the DNA components – 5`-adenosine monophosphate (5`-AMP) under the conditions specially designed to simulate the space environment. In order to synthesise 5`-AMP it is required to combine adenosine and inorganic phosphate. On the Earth the reaction goes in the solution, but there are no solvents whatsoever in space, therefore the researchers dried them in the air and got a pellicle. Synthesis requires energy. The major source of energy in the outer space both at present and in the prebiotic period of the Earth history has been the solar ultraviolet radiation of different wavelengths. Therefore, the pellicles were irradiated by a powerful ultraviolet lamp. Naturally, the synthesis was carried out in vacuum, and the researchers used the lunar soil, delivered to the Earth by the `Moon-16` station from the Sea of Abundance, as a model of the comet, meteorite, interplanetary or cosmic dust. The soil represented basaltic dust of the dark-grey colour, the diameter of its particles being less than 0.2 millimetres.
After 7-9 hours of ultraviolet irradiation of the dry pellicles the scientists acquired several compounds, mainly 5`-AMP, one of the DNA/RNA monomers. The energy of radiation does not promote synthesis alone, it also facilitates decomposition of the initial and newly-synthesised compounds, the more powerful the radiation is, the more extensively the decomposition goes. However, the lunar soil provided some protection. It has appeared that a small pinch of the lunar soil protects organic substances from the destructive ultraviolet impact – the lunar soil helps to increase the 5`-AMP yield by 2.7 times.
The researchers have made a conclusion that the organic compounds synthesis could have happened in the outer space environment. The synthesis could have taken place on the surface of space bodies at the initial phases of the solar system formation, along with that the chemical evolution (formation and selection of complex molecules) could have started in space. By the time the Earth was formed the chemical evolution might have approached the phase to be followed by the biological evolution. That implies that life on the Earth most probably did not start from the elementary organic molecules synthesis, but commenced from the polymers formation phase or from a further stage. Hopefully, the above assumptions will help the scientists to deeper penetrate into the mystery of the accelerated development of life on the Earth when the latter was quite a `young` planet.
Informnauka (Informscience) Agency. April 2002.