The fossil record goes back through the Phanerozoic eon, about 540 million years, and even earlier, into the Ediacaran period.  But while the fossils provide incontrovertible evidence of ancient life, the fossils themselves are certainly not alive.  In fossils, the original organic matter belonging to the fossilized life form has been replaced by inorganic materials, cast into the shape formerly occupied by the life form.  However, in some situations, the original organic matter does survive.  For example, original spores as old as 350 million years have been identified using their original organic material.  And DNA can survive for as much as a million years.  But in 2019, bacteria that had been buried 100 million years with barely any access to nutrients were not only identified but shown to be alive.  Had they been in suspended animation for all that time?  Or were they managing to eke out a living using much less energy than was previously thought to be necessary?
Steve D’Hondt is a Professor of Oceanography at the University of Rhode Island.  He studies life beneath the sea floor and was on the team that discovered bacterial cells living in 100 million-year-old sediment.
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