Molecular Timescales

Some remarkable fossil discoveries have been made of Neoproterozoic organisms in recent years (Xiao et al, 1998; Chen et al., 2004; Yuan et al, 2005) but the fossil record of this time period, and of earlier time periods, is much poorer than that of the Phanerozoic. For this reason, it is more difficult to estimate times of divergence between lineages from the fossil record alone, placing more importance on obtaining such estimates using molecular clocks. Below, we review those studies that have estimated divergence times of organisms that lived during the Precambrian, with emphasis on studies using relatively large data sets. Such information is critical to understanding how features of the planetary environment, including global glaciations, plate tectonics, and changes in atmospheric gases, influenced or were impacted by the evolution of life at that time.

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