ABSTRACT

The geological record of life from 3.5 × 109(Ga) years ago to 0.57 Ga ago is considered within the framework of published phylogenies derived from molecular biology. The earliest steps in evolution are not recorded in any known rocks. The record starts 3.5 Ga ago, with coccoid and filamentous benthic anaerobic photoautotrophs (Eubacteria). Evidence for methanogens (Archaebacteria) is found in rocks 2.8 Ga old, but because of the paucity of ancient rocks, of relevant research, and of means for recognising these organisms in the geological record, this is only a minimum estimate of the age of this group. The oldest eukaryotes seem to be about 1.4 Ga old; megascopic algae have a record back to 1.3 Ga, metazoans tentatively to about 1.0 Ga and protists back to 0.8 Ga. No Fungi are known from the Archaean or Proterozoic. The geological record is consistent with, but at present cannot test, phylogenies derived from the sequencing of proteins and nucleic acids. Nevertheless, it does provide a time calibration, and is consistent with at least one major prediction made using the ‘molecular clock’ approach: that the initial divergence of the animal phyla began about 1.0 Ga ago.