Early planetary environments and the origin of life1. Early planetary environments

The Earth accreted from planetesimals 4.6 Ga1 ago. The first few hundred million years were unfavourable for any kind of organic synthesis. Available evidences indicate that the time window for the origin of life on Earth is between 4.1 and 3.8 Ga ago. This period coincides with the late heavy bombardment of the inner Solar System by comets and asteroids and is too short for a complex system as life to have evolved from prebiotic chemistry. It is, therefore, speculated that at least some of the precursor organic compounds were impact-delivered to the early Earth by comets. These extraterrestrial bodies also supplied much of the Earth’s volatiles.