The Precambria2 - apparent complexity that even more...

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The Precambrian The Archean Eon encompasses the time from the formation of the earth until 2.5 billion years ago. The rocks formed during this eon are the most ancient rocks known, up to 3.96 billion years old. The nature of this rock inducates that there were/are even older rocks that, if they still exist, have yet to be located and dated. Perhaps the biggest development during the Archean was the first appearance of life. The earliest forms of life were simple prokaryotic cells, in a few cases remarkably similar to living prokaryotic forms (at least in terms of observable cell structure and size). Fossil evidence supports the origins of life on earth earlier than 3.5 billion years ago. Specimens from the North Pole region of Western Australia are of such diversity and
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Unformatted text preview: apparent complexity that even more primitive cells must have existed earlier. Rocks of the Ishua Super Group in Greenland yield possibly the fossil remains of the earliest cells, 3.8 billion years old. Life appears to have begun soon after the cooling of the Earth and formation of its atmosphere and oceans. These ancient fossils occur in marine rocks, such as limestones and sandstones, that formed in ancient oceans. The organisms living today that are most similar to ancient life forms are the archaebacteria (the archaea in modern usage). This group is today restricted to marginal environments. Recent discoveries of life at mid-ocean ridges add yet another possible place of origin: at these mid-ocean ridges where heat and molten rock rise to the earth's surface....
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