Pyrolysis of simple amino acids and nucleobases: survivability limits and implications for extra-terrestrial delivery

The idea of extraterrestrial delivery of organic matter to the early Earth is strongly supported by the detection of a large variety of organic compou nds in the interstellar medium, comets: and carbonaceous chondrites. Whethe r organic compounds essential for the emergence and evolution of life, part icularly amino acids and nucleic acid bases found in the meteorites, can be efficiently delivered by other space bodies is unclear and depends primari ly on capability of the biomolecules to survive high temperatures during at mospheric deceleration and impacts to the terrestrial surface. In the prese nt study we estimated survivability of simple amino acids glycine, L-alanin e, alpha-aminoisobutyric acid, L-valine and L-leucine), purines (adenine an d guanine) and pyrimidines (uracil and cytosine) under rapid heating to tem peratures of 400-1000 degrees C under N-2 or CO2 atmosphere. We have found that most of the compounds studied cannot survive the temperatures substant ially higher than 700 degrees C; however at 500-600 degrees C, the recovery can be at a percent level (or even l0%-level for adenine: uracil, alanine, and valine). The final fate of amino acids and nucleobases during the atmo spheric deceleration and surface impacts is discussed depending on such fac tors as size of the space body, nature and altitude of the heating, chemica l composition of the space body and of the atmosphere. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.