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9 October 2007 Searching for an alternative form of life on Earth
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Abstract
Biologists tacitly assume that all life on Earth descended from a common origin. This assumption is based on biochemical similarities and gene sequencing, which enables organisms to be positioned on a common tree of life. However, most terrestrial organisms are microbes, and it is impossible to deduce their biochemical nature from morphology alone. The vast majority of microbes remain unclassified, leaving open the possibility that some of them might be an alternative form of life, arising either from an independent origin, or representing a hitherto overlooked very ancient branch of the known tree. Thus there may exist an extinct, or even extant, shadow biosphere. I discuss various research proposals for locating and identifying "alien" organisms on Earth, both ecologically separate and ecologically integrated.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
P. C. W. Davies "Searching for an alternative form of life on Earth", Proc. SPIE 6694, Instruments, Methods, and Missions for Astrobiology X, 66940K (9 October 2007); https://doi.org/10.1117/12.742355
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