What caused the Delivery and retention of organics and volatiles through Earth History?
Mass extinctions are short-term events that kill off a significant proportion of a planet’s biota, and on Earth have been of greatest consequence to more complex organisms such as metazoans. Surface life is vulnerable to major planetary catastrophes, for example, impact of a large comet or asteroid, radiation and particles from a nearby supernova, or catastrophic climate changes such as intense intervals of greenhouse heating or Snowball-Earth type episodes. It is now known that at least one of the major mass extinctions was caused by large body impact, and we would very much like to know if others as well are related to this. The major line of study involves the study of impact craters and their history. Impact cratering involves evaluation of projectiles, which to first order, is a measure of the asteroids and comets passing in near Earth space. More broadly it involves the origin of those object, the orbital evolution of the time of their existence, and at least in the case of aster
