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 compounds in the interstellar medium, comets: and carbonaceous chondrites. Whether organic compounds essential for the emergence and evolution of life, particularly amino acids and nucleic acid bases found in the meteorites, can be efficiently delivered by other space bodies is unclear and depends primarily on capability of the biomolecules to survive high temperatures during atmospheric deceleration and impacts to the terrestrial surface. In the present study we estimated survivability of simple amino acids glycine, L-alanine, alpha-aminoisobutyric acid, L-valine and L-leucine), purines (adenine and guanine) and pyrimidines (uracil and cytosine) under rapid heating to temperatures of 400-1000 degrees C under N-2 or CO2 atmosphere. We have found that most of the compounds studied cannot survive the temperatures substantially 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 atmospheric deceleration and surface impacts is discussed depending on such factors as size of the space body, nature and altitude of the heating, chemical composition of the space body and of the atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved.