The development and diversification of Precambrian life

During the past decade, important strides have been made toward deciphering the paleobiology of the Precambrian Eon, the earliest seven-eighths of Earth history. This progress has accured chiefly from micropaleontological and organic geochemical studies of fine-grained, ancient cherts. Although understanding of the early biota—of its composition, diversity, paleocology and evolution—still remains far from adequate, three particularly significant generalizations have emerged: (i) Living systems were extant earlier than about 3000 m.y. ago; (ii) between about 3000 and 1000 m.y. ago, the Earth's biota was dominated by prokaryotic blue-green algae; and (iii) the development of the nucleated, eukaryotic cell type somewhat earlier than 1000 m.y. ago led to a stage of rapid diversification that culminated with the appearance of megascopic life near the close of the Precambrian. Consideration of these generalizations, and of the evidence bearing on them provides a ‘state-of-the-art’ assessment of the current status of Precambrian paleobiology.