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The Fossil Record - life forms are the archaebacteria(the...

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The Fossil Record 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 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. The oldest known rocks on earth are 3.96 Ga and are from Arctic Canada. Thus, life appears to have begun soon after the cooling of the earth and formation of the 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
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Unformatted text preview: life forms are the archaebacteria (the archaea in modern usage). This group is today restricted to marginal environments. Recent discoveries of bacteria at mid-ocean ridges add yet another possible origin for life: at these mid-ocean ridges where heat and molten rock rise to the earth's surface. Many of the ancient phototrophs and heterotrophic bacteria lived in colonial associations known as stromatolites. Cyanobacteria are on the outer surface, with other photosynjthetic bacteria (anoxic) below them. Below these phottrophs are layers of heterotrophic bacteria. The layers in the stromatolites are alternating biogenic and sedimentologic in origin. A modern day stromatolite is shown in Figure 20....
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