PROTEROZOIC EON (2 500-541 Ma)
From Greek próteros (first) and zõon (animal).

PALEOPROTEROZOIC ERA  (2 500-1 600 Ma)
From Greek palaiós (ancient), próteros (first) and zõon (animal).

Main events: the first global glaciation.

Lifeforms: the number of anaerobic organisms decreased until almost their extinction.

Paleoenvironment: according to the theory of the "Snowball Earth", the entire surface of the planet was an icy mass for 300 million years.