The Proterozoic Eon
What was going on?
The first continents have formed. Free oxygen finally reaches a level which will support
more complex forms of life. Eukaryotic single-celled life evolves. Simple multicellular
life appears towards the end.
What were the continents like?
The first real continents for which we have a geologic record appear at the start of the
proterozoic.
What are sediments from the Proterozoic like?
Proterozoic sediments still appear primarily in cratons, but we have a much better record
of sedimentary rock than for the Archaean. Also, banded iron formations appear, showing the
process of oxidizing surface iron; until almost all of the surface iron was oxidized, the
oxygen level in the atmosphere could not increase, and thus more advanced forms of life --
which need oxygen for respiration -- could not evolve.
What kind of life existed?
The proterozoic was a busy time for evolution. First, photosynthetic prokaryotes converted
enough carbon dioxide in the atmosphere into oxygen to oxidize the iron on the surface,
and allow the formation of free oxygen in the atmosphere. Then the first eukaryotes appear --
organisms (all single celled thus far) whose cells have a real nucleus and organelles.
Finally, towards the end of the eon, shortly before the Cambrian, we find the first
multicellular organisms, such as those in the Ediacaran fauna.