Impacts of minor bodies onto planets have obviously affected their habitability and the development of ecosystems during all stages of their history. On the one hand impacts may have supported the formation of life: comets and carbonaceous chondrites may have beenimportant sources of water (Morbidelli et al., 2000; Dauphas, 2003) and pre-biotic molecules (Montmerle et al., 2006) to seed the surface of the planets. On the other hand impacts pose a significant threat for developed biospheres (Chicxulub impact event, Alvarez et al., 1980; Smit, 1999). If the impact event at the end of the Cretaceous period had not happened, evolution may have progressed very differently. While the present dominance of mankind may have depended on that event, there is nothing to stop a future impact terminating it and paving the way for our successors. The influence of the rate, size distribution and composition of impactors on the evolution of life is a largely unstudied field. Pre-biotic materials may have been transferred from comets to Earth and other planets; alternatively life may have been triggered by chemical reactions and heat input caused by impacts. Brecciation and impact melting of the target may have led to rather long-term surface and subsurface hydrothermal activity and may have provided – in addition to volcanic environments - a perfect habitat for the origin of life and its continued evolution, in particular during the early Achaean time (Cockell et al., 2002; Westall and Folk, 2003).
Our goal is an evaluation of the consequences of impact events, such as the Early Heavy Bombardment (EHB, > 3.8 Ga ago), for the early phase of development of life on Earth (Archean and early Proterozoic; Simonson and Glass, 2004) and other planets, and the effects of single large collisions on the origin and evolution of planetary biospheres.
To study the role of impacts in such a broad context specific models for the origin, composition and textural parameters, such as porosity, of the different impactor types (important constraints are provided by space missions such as Hayabusa, Deep Impact, Stardust and Cassini), and of hypervelocity impact processes on various planetary surfaces and target layers (solid crust, ice, water, atmosphere), are required.