chapter 6c evidence of the past. paul sereno……1995 found dinosaur skull 1.5 m long...
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CHAPTER 6C
• EVIDENCE OF THE PAST
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Paul Sereno……1995
• Found dinosaur skull 1.5 m long
• Paleontologist – use fossils to reconstruct the past
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Fossils
• Trace remains or imprints of living organisms that are preserved by geological processes.
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The Age of Fossils
• Relative Dating – estimating the age of rocks or fossils by their depth in sedimentary rock
• Absolute Dating – measuring the time it takes for an unstable atom to decay
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Absolute Dating
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The Geologic Time Scale
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Mass Extinctions
• When a species dies out
• Scientists feel that the dinosaurs died out so quickly because of a fast changing environment
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The Changing Earth
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Precambrian Time
• Grand Canyon Bottom
• 4.6 billion yrs ----- 542 million yrs
• Life began here
• Atmosphere was CHAOTIC
• NO Oxygen early on
• 1st prokaryotes
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Precambrian Time
• 2nd – Cyanobacteria
• Photosynthesis and oxygen -- ozone
• NOW life on earth surface
• 1 billion yrs ago
• Multicellular organisms
• eukaryotes
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Paleozoic Era
• 542 million -- 251 million
• WATER – sponges, corals, snails, squids, trilobites, fish, sharks
• LAND – ferns, mosses, horsetails, conifers
• NO flowering plants
• Insects
• Salamander-like animals
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Paleozoic Era
• END of REPTILES and winged insects
• MASS EXTINCTION – 90% of water species are gone
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Mesozoic Time
• 251 million – 185.5 million
• “Middle Life”
• Age of Reptiles– Dinosaurs– Birds– Conifers– Flowering Plants
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Mesozoic Time
• EXTINCTION ??????????
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Cenozoic Time
• 65 million – today
• Recent Life
• Age of Mammals– Mastodons– Saber toothed cats– Camels, sloths, small horses– Humans
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Cenozoic Time
• ICE AGE
• Organisms moved to Equator to live or become extinct