Astrobiology is the multi-disciplinary field devoted to the investigation of the origin; physical, chemical and environmental limitations; and the distribution in space and time of life on Earth and in the Cosmos. Astrobiology seeks an answer to one of the most fundamental of all questions: — Is Life Restricted to Planet Earth or is Life a Cosmic Imperative? Understanding the characteristics, properties, habits, and diversity of living organisms on Earth is crucial to determining where and how to search for evidence of life elsewhere. New techniques and methodologies must be developed in order to determine a suitable suite of valid biomarkers that is needed to facilitate the differentiation of abiotic processes from true signatures of life. This is crucial to establishing the criteria needed to properly evaluate potential biosignatures in ancient Earth rocks and in a wide variety of Astromaterials (e.g., meteorites, interstellar dust particles and samples returned from future space flight missions to comets, asteroids and Mars).

It is well known that microbial extremophiles (e.g., prokaryotes such as archaea and bacteria) were the first life forms to appear on Earth. They are also the most abundant and the most widely distributed life forms on our planet. Extremophiles inhabit deep ice, deep crustal rocks, hydrothermal vents, permafrost and the deepest layers of the Antarctic Ice Sheet, deep marine sediments, acidic brines and hypersaline, alkaline lakes and lagoons. They live in the most hostile environments of our planet, growing wherever there is a source of water, energy, and carbon compounds and represent good analogs for life forms that may be present elsewhere in the Solar System Their life processes result in the production of biominerals, chiral amino acids, biological fractionation of stable isotopes, macromolecular fossils, chemical biosignatures and microfossils.

This "Perspectives in Astrobiology" volume includes papers treating a wide variety of these topics. They range from considerations of relict microbial communities of extreme environments (e.g. hydrotherms, hypersaline lagoons, and soda lakes and the subglacial Antarctic ice sheet) to complex organic molecules such as sugars under prebiotic conditions, biominerals and biotic and abiotic framboidal microstructures in Earth rocks, the processes of mineralization and fossilization of cyanobacteria, and biomarkers and microfossils detected in carbonaceous meteorites. Other papers discuss the use of stable isotopes and their biological fractionation as a baseline for evaluating extraterrestrial evidence and the use of chirality and composition of indigenous amino acids for differentiating between terrestrial and extraterrestrial organic matter in Astromaterials. Also treated in this volume are geomorph parallels, sediment patterns, and cyclicities in permafrost sediments of Earth and Mars; the survival of bacteria in space, eclipsing binaries, and advanced DNA and protein chip technology for future robotic missions to search for life in the Solar System.

Richard B. Hoover, Alexei Yu. Rozanov, Roland Paepe