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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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• To interpret history correctly, must understand what sorts of organisms are likely to be preserved? • What sorts of environments are
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This note was uploaded on 09/28/2008 for the course BIOEE 2780 taught by Professor Geber during the Fall '07 term at Cornell.

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

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