Terrestrial accretion of prebiotic volatiles and organic molecules during the heavy bombardment

Abstract

The possible prebiotic importance of impacts of carbonaceous chondrites and comets has a speculative history extending back at least to the beginning of this century (Chambeflin and Chambeflin, 1908). Such speculations have received support from modern nonhomogeneous terrestrial accretion models 0Nasson, 1971; Turekian and Clark, 1975; Anders and Owen, 1977), as well as dynamical models for outer planet formation (Fernandez and Ip, 1983; Shoemaker and Wolfe, 1984), in which Earth receives the bulk of its surface volatiles as a late-accreting impactor veneer. However, independently of solar nebula chemistry or planetary formation models, we may ask what the observed lunar cratering record tells us about terrestrial accretion of key prebiotic volatiles (e.g., carbon, nitrogen, and water) and organics during the period of heavy bombardment 4.5 to 3.5 billion years ago. This approach has the advantage of minimizing the conclusions' model-dependence, by basing the calculations as much as possible on the available extant data.