presentation_4 - Lecture 4 Fossil Record I Geologic Column...

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Lecture 4 Fossil Record I
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EON ERA PERIOD MYA LIFE FORMS PHANEROZOIC CENOZOIC Quaternary 1.8-present Early Homo Tertiary 65-1.8 First Horses MESOZOIC Cretaceous 144-65 First Flowering Plants/Dinosaur Extinction Jurassic 206-144 First Mammals Triassic 251-206 First Dinosaurs PALEOZOIC Permian 290-251 First Mammal-like Reptiles Permian Extinction Carboniferous 353-290 First Reptiles Devonian 409-353 First Insects Silurian 439-409 First Jawed Fishes Ordovician 495-439 First Fish Cambrian 543-495 “Cambrian Explosion” PROTEROZOIC 2500-496 First Eukaryotes ARCHEAN 3600-2500 First Bacteria HADEAN 4600-3600 Geologic Column 12%
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In some places, like the Grand Canyon, there is an extraordinary record of sedimentation and igneous flows. A long history of fossils is preserved and these can be assigned relative and absolute dates.
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Fossil of marine sponge from Kaibab formation ~50 mya Kaibab Formation
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Grand Canyon Supergroup 1 bya Stromatolite deposits By-products of bacterial growth
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How do we derive the geological time scale? Integrate across many stratigraphic columns from independent sites. William Smith (early 19th century British engineer, surveyor, canal builder) noted that rocks from different localities contained same unique fossil assemblages. He reasoned that rocks with same assemblages had been deposited at same time. Reliance on index fossils - abundant fossils with short time range and widespread distribution.
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Foraminifera: marine protozoans with test or skeleton (usually calcium carbonate) Important as index fossils because of wide distribution and (for each type) short stratigraphic range
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Fossils as Evidence of Past Life Fossils provide direct evidence about the history of life, but the record is incomplete and biased toward the preservation of certain organisms.
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Fossils as Evidence of Past Life • To interpret history correctly, must understand what sorts of organisms are likely to be preserved? • What sorts of environments are favorable for preservation?
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What Gets Preserved?
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