Insights into the Possible Composition of a Martian Biota

In the half-century since the Viking Mission's imaginative, trail-blazing effort to detect extant life on Mars, much has been learned about the current and past martian environment, the biology and ecology of Earth's present-day microbial biota, and Earth's most ancient fossils, a preserved record of life inhabiting environments much like those then prevalent on Mars. Earth's earliest known biota was entirely anaerobic-as would be expected of all lifeforms on Mars, whether past or present-composed of at least four principal lineages: sulfuretum microbes, photosynthetic bacteria, methanogenic archaea, and methanotrophic archaea. Given their existence on the early Earth, it seems reasonable to suggest that similar lineages might also have originated on Mars and, if so, might subsequently have coevolved with and adapted to the slowly changing martian environment to continue to be extant even to the present day.