Isotopic confrmation of the oldest clear microbial fossils


Textbook readings

None - this is a new paper

Notes, Comments and Updates

Bill Shopf, et al, 2017 SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions. PNAS 115:53-58

"Fossils" are the traces of previous life. Fossils can range from the actual remains of an organism (e.g. an amberized insect) to scant traces of unusual isotope ratios (e.g. the Greenland banded iron formations). The further back in time you wish to examine, the harder it gets to obtain and interpret these fossils. Samples are harder to get because of plate tectonics - really old rocks are actually quite rare, since most have been heavily or completely transformed by passage into the mantle. Before about the Cambrian explosion, when all or nearly all of the animal phyla appeared a short 540 Mya, only microbial fossils exist. In later formations these are common, but very old fossils are few and far between. Most of these have been found in Australia and Greenland, where the oldest untransformed deposits reside. Here we'll talk about evidence for microbial life early in Earth's history.

This paper describes carbon isotope analysis of some famous apparent 3.5Myo microbial fossils, supporting the hypothesis that these really are microbial fossils. Young fossils like this would never be doubted, but extreme claims (and the age of these fossils makes this an extreme claim) require extreme evidence, and perhaps this paper provides this.