This book explores the possibility that life exists on Mars. It provides an interdisciplinary overview of the early evolution of life in hydrothermal ecosystems on Earth, focusing on the problem of remote sensing and incorporating geological work relevant to the search for evidence of early life on Earth and Mars. It discusses the belief that studying thermal spring deposits as part of this search may be the best opportunity to test whether life on earth is a "unique experiment," or whether there is life elsewhere in the solar system. Hydrothermal ecosystems can be expected to have existed on Earth since life arose. A hyperthermophilic lifestyle has been proposed for the common ancestor of life and submarine hydrothermal vents are a candidate site for the origin of life. An origin of life at high temperatures appears most probable, although an alternative hypothesis has hyperthermophiles as the only survivors of bolide impacts during the last stages of planetary accretion. Our interest in these ecosystems stems in part from research to develop strategies for the search for fossil life on Mars. This may well be our best opportunity in the near future to test whether life on Earth is a unique experiment, or whether there is, or was, life elsewhere in the Solar System (and by extension, the Universe).
In search for analogous fossil systems on Earth it is unfortunate that the palaeobiology of ancient hydrothermal ecosystems is almost completely unknown. This is because of lack of research on this topic, not absence of deposits on which to work. As a result of mineral exploration, many fossil subaqueous and subaerial spring systems are known: numerous gold and base metal deposits of all ages back to Archaean are in such ?exhalative?, ?epithermal? and ?Kuroko-style? systems. This book focuses attention on the history of high temperature ecosystems, bringing together biologists working on extant systems, especially from the point of view of microbiology and molecular phylogeny, with palaeobiologists working on ancient examples or who are familiar with microbial palaeobiology, geologists who know how to find such systems and who know what their tectonic, mineralogical and geochemical characteristics are, and planetary geologists who have a chance of finding such systems elsewhere.