Chapter-8.docx - Chapter 8 In 1796 Thomas Jefferson...

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Chapter 8 - In 1796, Thomas Jefferson presented finding of bones of extinct ground sloth in Virginia to American Philosophy Society. - William Smith realized that strata contain fossils of extinct life-forms, hypothesizing the position of strata and the kind of fossil to be the same throughout England. - Study of fossils centers around 2 components: time & environment 1. Fossils - They are remains of organisms that have been transformed into rock through chemical replacement. - The replacement process: Ca and P in bones and teeth are replaced with rock-forming minerals (Fe and Silica). - Bones and teeth are the most common source of fossils (99%). - Organism will not become a fossil if: Left exposed on ground surface for any length of time. Not staying in an oxygen-free (anoxic) environment - Fossils can be found in many types of rock, but most commonly in sedimentary rock. - Fossilization occurs when animal remains are buried in volcanic ash. Limitation - Representation is the important factor in creating a fossil record - Key stages of past life are missing because: Paleontologists only searched for fossils in some places; hence, not discovering all fossils Fossils are reserved in some places and not in others Fossils in rocks are not always complete. - Taphonomy: study of what happens to an organism’s remains - Sedimentary: rock formed when deposition of sediments (trầm tích) creates distinct layers (strata) 2.
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