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Chemia radiacyjna i powstanie życia na Ziemi

Zagórski P.

Wiadomości Chemiczne

2001

[Z] 55, 11-12

965-985

Radiation chemistry, i.e. the chemical changes initiated by the absorption of ionizing radiations, have to be considered in three chapters of discussions on the mechanisms of origins of life on Earth. i: Much higher level of ionizing radiations on Earth than now, has given rise to intensive radiation chemistry. It played an important rôle in the formation of prebiotic organic compounds, by the abstraction of electrons from simple compounds, and leaving positive species, also very reactive. In the subsequent processes, free radicals were formed, which created new combinations and even the formation of compounds of increased molecular weight; chemical chain reactions were also initiated, all entirely at ambient temperature. However, all these reactions were not chiral in their nature, and, as far as the experiments indicate, were not able to replicate or to be amplified. ii: In the stadium of the creation of life in the "soup" formed by different variations of high energy chemistry, radiation chemistry does not seem to be important. In spite of initial great hopes, created by physicists, the reactions initiated by ionizing radiations were of low enantioselectivity i.e. were not able to enrich one of the enantiomere, or amplify effects which could appear initially. In particular, the hopes laid in the role of the violation of parity, e.g. in the case of b-radiation, as the force promoting chirality, were not fulfilled [c.f. 16]. iii: In the lack of reasonable mechanisms for the origins of life on Earth, many researchers are looking for origins of life from the outside of the Earth. However, that approach does not solve the problem of chiral synthesis and creates additional problems of the transportation of living matter. In that respect the radiation chemistry and its biological consequence - radiobiology is univocal: ionizing radiations, filling the universe, of action extended for years, cause total inactivation of every life, even the primitive one, like in the shape of viruses. The main destructive chemistry is dehydrogenation of live organisms and dry spores, which occurs even at low temperatures, close to absolute zero. Much lower doses, of single Gy (grays) to the whole body are sufficient to destroy the human life, already during the travel to and back from Mars. The shielding atmosphere of gases around the Earth is equivalent to 10 meters thick layer of concrete. A construction and operation of a ship, which could secure the survival of the crew, by making conditions of radiation background as safe as on Earth, is impossible. For the same reasons, radiation chemistry excludes the arrival of "aliens", E.T. etc on Earth. Radiation chemistry does not exclude the possibility of Life in any part of the Universe, sufficiently shielded, but shows impossiblity of the transportation of live precursors of our life to the Earth. The Life on Earth originated here and any models of its formation, if true, have to be a subject of reconstruction in the laboratory.