1.2: Prokaryotic World

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Most of the Proterozoic prokaryotes (Monera) dominated the living world. Typical landscape these times was high, almost vertical rocks and shallow plains, which should be covered with the tide for dozens of kilometers. This is because there were no terrestrial organisms decreasing erosion. Ocean was low oxygenated; only water surface contained oxygen.

In those conditions, ancestor of eukaryotes appeared. First eukaryotes could probably remain contemporary heterotrophic Excavata (Fig. 2.2.3) like Jacoba, but there are no fossils of this kind. However, there is a number of fossils which could be treated as algae, photosynthetic protists. These fossils remind contemporary red and green algae (Fig 2.2.9, the bottom row). It is possible that some other Proterozoic fossils (acritarchs) belong to other protist groups, for example, unicellular Dinozoa (Fig. 2.2.8).

Ecosystems of these times were similar to Archean and mostly consisted of cyano- and other bacteria, and represented now by stromatolites. No one can say anything about terrestrial life in Proterozoic, but it possible that Monera dominated there as well.

At the end of middle Neoproproterozoic, continents of Earth joined in one big continent Rodinia; this triggered the most powerful glaciation in history, “snowball Earth”, Cryogenian glaciation.