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 & environment1.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 fossilsFossils are reserved in some places and not in othersFossils 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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