Thermal ecosystems are biologically simple. These systems contain a few species of unicellular organisms and may resemble ecosystems that existed on the ancient earth during the early stages of biological evolution. The analysis of fatty acids from some bacteria-algal mats in streams draining hot springs in Yellowstone National Park show distributions resembling those of fatty acids isolated from ancient cherts. A layered silica deposit, "stromatolite," taken from the perimeter of an alkaline hot spring was used as a modern analog of bedded chert deposits. The distributions of fatty acids from the surface, crust, and interior regions of the stromatolite indicate that the acids are syngenetic with the silica deposition, and that acid distributions have not changed signific ntly during the time of formation of the "stromatolite" (10²-10³ years).

Comparisons were made of fatty acids and hydrocarbons from natural ecosystems and laboratory cultures of thermophiles. Marked differences were observed between the distributions of the fatty acids and alkanes in the specific samples and of the fatty acids from different ecosystems.

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