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07_fossils_num_dating_10_post - 07 Geologic Time 2 Fossils...

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ure 07: ure 07: 1 07: Geologic Time 2: Fossils, Absolute Dating, Age of Earth http://www.nrc.gov/
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ure 07: ure 07: 2 Why this is important The changing fossil record allows geologists to determine the relative ages of rocks and to demonstrate the time-equivalence of rock units from around the world. Fig. E.2b Fig. E.2b
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ure 07: ure 07: 3 Why this is important The fossil record, the length of geologic time, the gradual nature of many geological processes, and Charles Darwin’s own geological investigations were instrumental in the development of his theory of natural selection. Ordovician (~475 million years ago) trilobite & brachiopod. Photo: R.M. Busch Devonian (~385 million years ago) trilobite & brachiopod. Photo: R.M. Busch Cambrian (530 million years ago) trilobites. Photo: C. Clark
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ure 07: ure 07: 4 Why this is important The decay of radioactive isotopes provides the ticking clock for dating geologic events, including the age of the Earth and the solar system.
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ure 07: ure 07: 5 Fossils Fossil : the remnant or trace of an ancient living organism that has been preserved in rock or sediment Fig. E.4 Fig. E.4
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ure 07: ure 07: 6 Types of fossils 1. Frozen or dried body fossils Frozen wooly Frozen wooly mammoth mammoth news.bbc.co.uk
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ure 07: ure 07: 7 Types of fossils 2. Body fossils preserved in amber (hardened tree sap) 3. Preserved hard parts bones teeth shells Fig. E.5b Fig. E.5b Fig. E.5c Fig. E.5c
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ure 07: ure 07: 8 Types of fossils 4. Replaced hard parts as a result of permineralization (process by which minerals precipitate in porous material like wood (forming petrified wood ) or bone from groundwater solutions that have seeped into the pores. Fig. E.5d Fig. E.5d
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ure 07: ure 07: 9 Types of fossils 5. Molds and casts of body parts : if a shell, for example, dissolves out of the enclosing rock, the cavity is a mold ; if the mold later fills in with material, it becomes a cast . cast cast mold mold mold mold cast cast
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ure 07: ure 07: 10 10 Types of fossils 6. Carbonized impressions of bodies: feathers, insects, leaves, etc., leave an imprint when pressed between layers of sediment; although most of the original organic material is later removed, insoluble carbon remains as a thin film.
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ure 07: ure 07: 11 11 Factors favoring fossilization 1. Death in an oxygen-poor environment prevents organic decay 2. Rapid burial: organism is enclosed in sediment before it can decay, be eaten, or disturbed by other processes. 3. Presence of hard parts (bones, shells, etc.). 4. Lack of subsequent deformation and/or metamorphism Because these conditions do not always occur, the fossil record is incomplete, but transitional forms do occur; this is evidence for evolution . http://evolution.berkeley.edu/
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ure 07: ure 07: 12 12 Mechanism of evolution Survival of the fittest.’ Survival of the fittest.’ http://evolution.berkeley.edu/
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ure 07: ure 07: 13 13 Evidence for evolution Bacteria reproduce very quickly, and new strains evolve through Bacteria reproduce very quickly, and new strains evolve through mutation in a matter of minutes and hours mutation in a matter of minutes and hours
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