Extremities:  Geology and Life in Yellowstone and Implications for Other Worlds


Biomarkers or biosignatures are signs or indications of life, present or past. The search for life on Mars is now zeroing in on indirect markers of life rather than extant life, as few reputable researchers think it reasonable that life-as-we-know-it could be found at the surface of Mars.

Striated Deposits
Weird Structure

Striations in ancient hot springs deposits near Twin Buttes View Spring, Mammoth Hot Springs complex. These are casts of microbial filaments, aligned by once-flowing water. If this structure were seen in a returned Martian sample, it would undoubtedly be considered a biosignature.
This bizarre structure, about a foot across, is in the outflow of Grand Prismatic Springs. It probably is a microbial colony, though we don't know for sure. If this were entombed in silica and preserved, it would be considered a biosignature, as its not clear how it could form without life.
fossilizing cypress

Biological structures can be preserved very quickly in hot spring deposits. This sprig of cypress is partially coated with calcium carbonate, even though the uncoated parts are still green! Canary Spring, in Mammoth Hot Springs.
On the other hand, not everything that looks biological is biological. These concentric circles look a lot like stromatolites, but are actually volcanic. They are lithophysae, and form in gas-filled bubbles in obsidian, as it cools after flowing (Obsidian Cliffs, field of view is ~ 2 feet). These are a fake biosignature (a dubiosignature).

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Updated 11/15/02.
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