Biosignature
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in that specimen because it was believed until recently that only bacteria could create crystals of their specific shape. Other potential biosignatures studied in the ALH84001 meteorite included putative nanofossils, tiny rocklike structures whose shape was a potential biosignature because it resembled known bacteria. Most scientists ultimately concluded that these were far too small to be fossilized cells.
From this point of view, even the hypothetical radio signatures that SETI scans for would be an electromagnetic biosignature, since a message from intelligent aliens would certainly demonstrate the existence of extraterrestrial life.
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[edit] The Viking Missions to Mars
The Viking Missions to Mars in the 1970s conducted the only thorough experiments to date which were explicitly designed to look for biosignatures on another planet. Each of the two Viking landers carried three life-detection experiments which looked for signs of biochemical metabolism.
More details can be found in the entry on the Viking Biological Experiments.
[edit] Biosignatures in Biology
In biology, biochemistry, and biomedical research, biosignatures are biological indicators obtainable through assays (such as a blood sample) which can be used to ascertain facts about an individual's health or disease state. Peptides and antibodies are examples of biochemical constructs that can be used to measure biosignatures and thus determine if, for example, a person has been infected with a particular disease, prior to their actually exhibiting symptoms.
[edit] Biosignatures in Geochemistry
In Geochemistry, Geobiochemistry, and Geomicrobiology, biosignatures are often used in a more precise fashion to determine which living organisms are or were present in a sample. For example, the particular fatty acids measured in a sample can indicate which types of bacteria and archaea live in that environment. When used in this sense, geochemists often prefer the term biomarker.
For example, long-chain fatty alcohols with more than 23 atoms are produced by planktonic bacteria and are their molecular marker in sediments. [1]
[edit] External links
- Biosignatures.org - at the Biodesign Institute at Arizona State University
