Proterozoic Eon – Oxygen Appears

Key Events

  • The Proterozoic Eon is a very active tectonic period.
  • Evolutionary advances lead to multicellular organisms.
  • Bacteria start to pump oxygen into the atmosphere, causing the ‘Great Oxygenation Event’.
  • Life thrives in the oxygenated atmosphere and chemical processes change.
  • Earth experiences its first glacial period around 2,450-2,220 million years ago, with a series of ice ages. There are several other glacial periods during the Proterozoic Eon.
  • From 635 million years onwards, soft-bodied multicellular life (similar to jellyfish and worms) starts to emerge.
Illustration of life during the Proterozoic Eon. Copyright: Vix Southgate

Facts, Debates & Trivia

  • The Proterozoic Eon is named after the Greek word for ‘earlier life’
  • Supercontinents form (e.g. Rodinia, around ~1,000-700 million years ago).
  • Some scientists propose that the whole Earth becomes entirely covered in ice during periods of millions of years, up to around 650 million years ago (the ‘Snowball Earth’ hypothesis).
  • On Mars, all liquid water dries up by 2,000 million years ago, leaving the cold, barren planet we see today.
Clint and the Earth Story Trail


  • Oxygen reacts with methane to create carbon dioxide.
  • As concentrations of methane (a ‘greenhouse gas’ that is very effective at trapping heat) decrease, the temperatures fall.
  • Iron is precipitated to make minerals like haematite.
The Earth 700 million years ago may have looked like something like this. Credit: C.R. Scotese/I. Webster.


2,500-541 million years ago

(1,959 million years)

1 metre = 
20 million years

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