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Biosignatures of early earthsA major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in Earth's modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on Earth for about 1(1/2) billion years before the buildup of atmospheric oxygen. Inferred characteristics of Earth's earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH(3)SH, the sulfur analog of methanol), may have been biogenic products on early Earth. Similar production could take place on extrasolar Earth-like planets whose biota share functional chemical characteristics with Earth life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-microm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.
Document ID
20050155260
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Pilcher, Carl B.
(NASA Headquarters Washington, DC United States)
Date Acquired
August 23, 2013
Publication Date
September 1, 2003
Publication Information
Publication: Astrobiology
Volume: 3
Issue: 3
ISSN: 1531-1074
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other

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