Precambrian
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Precambrian
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from 4,600 to 590 million years ago The sun and solar system formed about 4,600 million (or, 4.6 billion) years ago from a vast cloud of interstellar hydrogen and helium, enriched with a sprinkling of heavier elements. These heavy elements (carbon, oxygen, nitrogen, etc...) made up only about 1% of the total mass of the cloud, but our eventual existence depended on them. These elements were forged deep inside stars which deposited their life's work back into interstellar space. Long before our sun was born, generations of stars lived and died, paving the road for the existence of Earth and the other rocky planets. Precambrian time includes Earth's history from birth up to 590 million years ago. That is, the Precambrian spans 90% of Earth's existence. Fossilized bacteria and blue-green algae show that primitive life existed at least 3,500 million years ago, and possibly earlier. Yet it took another 2,100 million years for eukaryotic cells (plant and animal cells) to appear. These single-celled creatures (protozoa) dominated the oceans. Multi-cellular animals (invertebrates) did not evolve until very late in Precambrian time, around 700 million years ago, or 2,800 million years after life first began on Earth. Late bloomers. The fossil collection in our museum begins about 750 million years ago, near the end of Precambrian time. The only multi-cellular life forms at the end of the Precambrian were in the oceans and included some groups that have survived until the present: jellyfishes and segmented worms (annelids). There was nothing yet on land except the wind.
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