Biogenicity of earth’s earliest fossils

Abstract

The abundant and diverse assemblage of filamentous microbial fossils and associated organic matter permineralized in the ~ 3465 Ma Apex chert of northwestern Australia—widely regarded as among the oldest records of life—have been investigated intensively. First reported in 1987 and formally described in 1992 and 1993, the biogenicity of the Apex fossils was questioned in 2002 and in three subsequent reports. However, as is shown here by use of analytical techniques unavailable twenty years ago, the Apex filaments are now established to be bona fide fossil microbes composed of three-dimensionally cylindrical organic-walled (kerogenous) cells. Backed by a large body of supporting evidence of similar age—other microfossils, stromatolites, and carbon isotopic data—it seems clear that microbial life was present and flourishing on the early Earth ~ 3500 Ma ago.