The development and diversification of Precambrian life

The temporal relationships among various prominent events occurring in the evolution of life are considered. It is seen that the Precambrian encompasses an enormous segment of geologic time and includes more than 80% of the history of life on this planet. As a result of the studies of the past decade it appears that living systems were probably extant as early as 3300 m.y. ago. Photoautotrophs, apparently including blue-green algae, originated earlier than 3000 m.y. ago. Blue-green algae were the dominant components of earth's biota for the period extending from about 3000 to 1000 m.y. ago. The nucleated, eukaryotic cell type had become established at least as early as 900, and possibly prior to 1300 m.y. ago.