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J. A. Baross (School of Oceanography/Astrobiology Program, U. Washington)
The definition and origin of life are key questions at the heart of astrobiology, yet we do not have a consensus definition of life, for this requires an understanding of the nature of living systems that has not yet been achieved. Such an understanding is critical for many areas of astrobiology, including the origin and evolution of life on Earth, the detection of extant or extinct life on other solar system bodies, and the possibility for alternative carbon-based life. Ultimately, the question ``What is life?" becomes reduced to listing canonical features of terrestrial life that can be used to construct models for the origin of life and to develop possible ``biosignatures" for detecting life elsewhere.
Origin of life studies have focused on the conditions during the first few hundred million years after Earth accreted, the sequence of chemical and biochemical steps leading to a living entity, the characteristics of the earliest microbial communities, and the events leading to greater complexity at the levels of individual cells, multi-cellular organisms and ecosystems. Theories on the origin of life range from the first living entity being clay crystals, protein or ribonucleic acid worlds (``RNA world"), metabolizing entities without information-containing molecules, or self-assembling membranes capable of capturing proteins and nucleic acids. It may be that in fact all of these theories played a role in the origin of life drama, perhaps at different times and places. Even though some experimental progress has been made, the origin of life remains one of the great-unsolved questions of science. Moreover, the possibility for multiple origins of life is an open question with profound implications for detecting life elsewhere in the universe
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.