Fossils | ||
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Fossils are preserved signs of life, usually dug up from rocks (hence the name from the Latin fossilis). Sometimes fossils are actual remains of life, such as bones. Other times fossils are stones and minerals that have replaced the remains in such a way that the minerals hold the shape of the original remains. Often, fossils are a mix of original remains and mineralized remains. There are also fossils that are made as impressions, molds, or casts in rock. Tracks, for example, can become fossils. The oldest fossils are microfossils (fossils of cyanobacteria) from about 3,456 million years ago (3.456 billion years ago). André Brack, in Origin of Life within the Encyclopedia of Life Sciences (2002) states that there is organic carbon in the greenstone belts of Isua in Greenland, and since those sediments are about 3.85 billion years old, we can guess that life was around at least by then. Analysis of the DNA of bacteria also suggests the Last Universal Common Ancestor may have lived more than four billion years ago.
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