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Astron. Astrophys. 354, L6-L8 (2000)

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1. Introduction

Understanding origin of life on earth is a very challenging astrophysical problem of today. Study of isotopic ratios on carbon inclusions in ferric salt deposits in Greenland shows that life existed on earth before 3.85 billion years (Mojzsis et al. 1996; Holland 1997; Schidlowski 1993) or possibly even before 4 billion years (Mukhin & Gerasimov 1993). On the other hand, data from isotope systematics show that the earth is between 4.55 to 4.57 billion years old (Faure 1986). The time available for life to develop on the earth from scratch is possibly around 0.5-0.6 billion years which is very short (Crick & Orgel 1973). One of the ways the formation of life on earth could be assisted if the building blocks of life, namely, amino acids and at least some of the bases of DNA could be produced well before the planetary formation, presumably during chemical evolution of molecular clouds. Whereas extensive work is present in the literature to study evolution of some of the organic and inorganic molecules, no work is reported so far which study the formation of bio-molecules or pre-biotic molecules such as amino acids, sugars, DNA, RNA etc.

Bases of DNA such as adenine ([FORMULA]) can be produced by successive addition of HCN molecules in four steps (Volkenshtein, 1983). In the present letter we perform a hydrodynamic simulation and followed chemical evolution during the molecular cloud collapse and show that a significant amount of adenine (with mass fraction [FORMULA]) could be produced. This indicates that planets and comets could have formed with contaminations of pre-biotic molecules. If correct, this may resolve a long-standing problem of origin of lives on earth.

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000