If the Archean was a prokaryotic world, the Proterozoic was a time of transition to a eukaryotic and eventually a multi-cellular world. Microfossils of eukaryotes appeared around the Paleoproterozoic-Mesoproterozoic boundary, and by the late Mesoproterozoic—early Neoproterozoic, the major algal clades were present. Eukaryotes (based on acritarch diversity) appear to have gradually increased in diversity until the mid-Neoproterozoic (~700Ma), the time of the first (Sturtian) Neoproterozoic glaciation. After the second glaciation (~630Ma), their diversity increased rapidly until the latest Neoproterozoic, when they underwent an extinction event.
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