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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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- Fall '10