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Fossils of Precambrian time
570 million to
1 billion years ago
2 billion to 3 billion years ago
3 billion to 3.4 billion years ago
4.6 billion years ago
Sponges, jellyfish, and primitive arthropods (trilobites)
First stromatolites
First primitive cells (algae) Earth formed
The first life found in rocks is dated at 3.4 billion years ago, a remarkably short time after the earth first came into existence. The rocks containing the world’s earliest known fossils are in South Africa; in them, microscopic life forms can be seen that are similar in shape to modern bacteria and blue-green algae.
A much more substantial form of life began to grow some 3 billion years ago, when large colonies of blue- green algae built themselves into large mats called stromatolites. At the same time, the algae began to secrete calcium carbonate, thus producing the world’s first fossils.
It took nearly 2 billion years for more sophisticated life forms to evolve. The first evidence
we have of them is from rocks 1.4 billion years old. They were early marine plants, able to get the energy they needed by using sunlight. As they used sunlight in the process of photosynthesis, they gave out oxygen, thus beginning a long process of change in the atmosphere that would eventually lead to the evolution of animals on land.
Evolution seems to have been much more rapid after the early plants developed. By 1 billion years ago there is evidence of worms, but the fossil record is so poor for this ancient time that little more is known.
It seems reasonably certain that evolution continued apace, but that all of the creatures were
(Below) Mats of algae that formed stromatolites were the first colonial form of life. They began
in the Precambrian and are still growing today. This makes them one of the most successful forms of life on earth.
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