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bioch22.1webpageNI - Paleobiologists analyze and categorize...

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Paleobiologists analyze and categorize fossils, which provide records of the past. Fossil Formation: Fossils are any form of evidence of life, including organic remains, moulds and impressions, and other traces of their existence. They are common around the world, but only a small percentage of all living things become fossils. This is because a dead organism must undergo certain environmental processes to fossilize. To become a fossil, a deceased organism has to undergo the least disturbance as possible. Sources of decay include wind/water erosion and other geological processes, microorganisms, scavengers and oxidation of the organic matter. (S1) The soft tissues of organisms are generally decomposed by bacteria before they are buried, so the hard bones, teeth and shells of animals are more likely to be preserved. It is most common for fossils to be formed in underwater environments because most of the earth is covered with water, and because there is less of a chance of decay there. (S1) The typical fossil is formed in sedimentary rock, from sand, silt and soil, which form layers over the dead organism. The pressure of subsequent layers of deposit (and perhaps the pressure from the water above) compresses the older layers into a rock fossil. (1) The Hypothetical Fossilization of a Fish: A dead fish sinks to the floor of the sea or lake. (S1) The soft parts of the fish (muscles, tendons, organs) are decomposed by microorganisms in the environment. (S1)
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Various debris (dust, silt, sand) fall on the skeleton of the fish. This burial usually happens quickly, through sudden
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