Philippe Claeys – författare

This review emerged from several interdisciplinary meetings and schools gathering a group of astronomers, geologists, biologists, and chemists, attempting to share their specialized knowledge around a common question: how did life emerge on Earth? Their ultimate goal was to provide some kind of answer as a prerequisite to an even more demanding question: is life universal? The resulting state-of-the-art articles were written by twenty-five scientists telling a not-so linear story, but on the contrary, highlighting problems, gaps, and controversies. Needless to say, this approach yielded no definitive answers to both questions. However, by adopting a chronological approach to the question of the emergence of life on Earth, the only place where we know for sure that life exists; it was possible to break down this question into several sub-topics that can be addressed by the different disciplines.

The main chapters of this review present the formation and evolution of the solar system (3); the building of a habitable planet (4); prebiotic chemistry, biochemistry, and the emergence of life (5); the environmental context of the early Earth (6); and the ancient fossil record and early evolution (7). The concluding chapter (9) provides the highlights of the review and presents the different points of view about the universality of life. Two pedagogical chapters are included; one on chronometers (2), another in the form of a "frieze" (8) which summarizes in graphical form the present state of knowledge about the chronology of the emergence of life on Earth, before the Cambrian explosion.

Based on material delivered at several summer schools, this book is the first comprehensive textbook at the graduate level encompassing all aspects associated with the emerging field of astrobiology.

Volume II gathers another set of extensive lectures covering topics so diverse as the formation and the distribution of elements in the universe, the concept of habitability from both the planetologists'' and the biologists'' point of view and artificial life. The contributions are held together by the common goal to understand better the origin of life, its evolution and possible existence outside the Earth''s realm.The volume ends with 120 pages of a very useful appendix comprising "Some Astrophysical Reminders", "Useful Astrobiological Data" and "An Astrobiological Glossary".

Despite their global importance, little is known about the few existing examples of impacts into marine environments and icy targets. They are among the least understood and studied parts of impact crater geology. The icy impacts are also of great importance in understanding the developments of the outer planets and their satellites such as Mars or Europa. Furthermore, the impact mechanisms, crater formation and collapse, melt production and the ejecta distribution are scarcely known for impact on targets other than the "classical" solid silicates of the continental crust. The reaction of water and ice to impacts clearly deserves a more thorough study. The understanding of  impact effects and consequences in the case of aqueous hits, soft sediments and icy targets has not been thoroughly explored and comprises the main focus of this book.

A number of papers in the field of hypervelocity impacts on ice are included. These cover a review of available literature in the field of laboratory studies of such impacts, large impact structures on Titan, predicting impact cratering on a comet nucleus, and a novel report on the survival of bacteria fired at hypervelocity into icy surfaces. This latter paper is concerned with astrobiology and in particular Panspermia (natural migration of life through space).