Comets and prebiotic organic molecules on early earth

Life on the Earth may have originated in the final throes of the heavy bombardment, although the evidence for this conclusion is uncertain. This bombardment could have rendered the Earth's surface inhospitable for life for hundreds of millions of years subsequent to terrestrial formation. It may also have delivered to the Earth's surface prebiotic organic molecules of relevance to the origin of life. The quantitative importance of these exogenous sources, in comparison with endogenous production, depends largely on the nature of the early atmosphere. This chapter reviews current controversies in these areas and presents the current best, albeit still tentative, estimates of endogenous and exogenous sources of organics, and resulting concentrations of organics in the Earth's early oceans, for a range of early Earth models.