EARLY ARCHEAN EVIDENCE OF LIFE Hints of Life >3500 Ma in Age

Unfortunately, even the most detailed studies of the ancient rock record are unlikely to reveal the how of life’s beginnings. Because all biomonomers and biopolymers are geochemically unstable, it is implausible that evidence of intermediate stages in the emergence of life could be preserved in ancient rocks. As to the timing of life’s origin, the geosciences can provide only a partial answer—paleobiological studies of microbe-produced stromatolites, cellular microbial fossils, and carbon isotope evidence of microbial physiology have set a minimum date for life’s existence, but none has revealed the actual age of life’s emergence. Such insight might be obtained by tracing biological signals back through time and, at a particular horizon in the rock record, see them vanish and be replaced in older units by evidence of planet-wide sterility. One might even hope to find carbonaceous deposits that could plausibly be interpreted as the residuum of a life-generating “primordial soup.” Such, however, is not the case. Here, again, the problem is one of preservation—not of remnants of life but of the geological record itself.