Titlebook: How Likely is Extraterrestrial Life?; J. Woods Halley Book 2012 The Author(s) 2012 Chemical evolution of life.Drake‘s equation discussed.E

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Biological Factors of life on earth is not known. A somewhat less obvious problem is that estimates of the factor . are very sensitive to the criteria which are used to identify the presence of life. Attempts to identify the essential features required to label a material system as ‘a(chǎn)live’ are numerous, and necessari

GLOSS

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Electromagnetic (SETI) Searchesgalaxy. However we found that the absence of evidence of colonization of earth by extraterrestrials could be used to put some bounds on the possible types of civilizations that might exist and, in particular was shown to indicate that civilizations with the desire and ability to migrate quickly betw

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Direct Searches for Primitive Forms of Lifeof extraterrestrial life, there are also limitations to this method of exploration. The biosphere or organisms may not produce observable radiation and some kinds of experiments, such as chemical analysis of soils, which are routine in studies of terrestrial life, are not possible. The NASA astrobio