Proterozoic

Lower Proterozoic Stromatolites from Bolivia, South America (polished vertical section through rock)

The Proterozoic eon comes before the Phanerozoic. It was a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life". The Proterozoic Eon extended from 2500 million years ago (mya) to 541 mya. It is the most recent part of the former Precambrian.

The Proterozoic consists of 3 geologic eras, from oldest to youngest:

• Palaeoproterozoic: 2500 to 1600 million years ago
• Mesoproterozoic: 1600 to 1000 mya
• Neoproterozoic: 1000 to 542 mya

The well-identified events were:

• Several glaciations, including the Snowball Earth during the Cryogenian period in the late Neoproterozoic.
• Rapid crustal segments collect into continents. Supercontinents Laurentia (Palaeoproterozoic) and Rodinia (Neoproterozoic) form.
• Early plate tectonics.
• Oxygenation of the atmosphere, the Great Oxygenation Event.
• Clean (unchanged by metamorphosis) sand and carbonate deposits occur for the first time.
• First eukaryote fossil at 2.1 billion years.^[1]p57
• The Ediacaran period (635 to 542mya) which is characterized by the evolution of abundant soft-bodied multicellular organisms.^[2]

Study of these rocks shows that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and mountain building.^[3]

Related pages

• Life timeline

References

1. Clarkson E.N.K. 1998. Invertbrate palaeontology and evolution. Blackwell, Oxford.
2. Levin, Harold L. 2005. The Earth through time. 8th ed, Wiley, N.Y. Chapter 9: The Proterozoic: dawn of a more modern world.
3. Stanley, Steven M. 1999. Earth system history. Freeman, N.Y.. ISBN 0-7167-2882-6.