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| Multicellular algae |
The period of Earth's history that began
2500 million years ago and ended 542 million years ago is known as the
Proterozoic Eon, which is subdivided into
three eras: the
Paleoproterozoic,
Mesoproterozoic and
Neoproterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic,
stable continents first appeared and began to accrete, a long process taking about a billion years. Also coming from this time are the first abundant fossils of living organisms, mostly
bacteria and
archaeans, but by about 1800 million years ago
eukaryotic cells appear as fossils too.
With the beginning of the Mesoproterozoic comes the first evidence of
oxygen build-up in the
atmosphere. This global catastrophe spelled doom for many bacterial groups, but made possible the explosion of
eukaryotic forms. These included
multicellular algae, and toward the end of the Proterozoic, the
first animals.
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