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CHAPTER 6C
• EVIDENCE OF THE PAST
Paul Sereno……1995
• Found dinosaur skull 1.5 m long
• Paleontologist – use fossils to reconstruct the past
Fossils
• Trace remains or imprints of living organisms that are preserved by geological processes.
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
Absolute Dating
The Geologic Time Scale
Mass Extinctions
• When a species dies out
• Scientists feel that the dinosaurs died out so quickly because of a fast changing environment
The Changing Earth
Precambrian Time
• Grand Canyon Bottom
• 4.6 billion yrs ----- 542 million yrs
• Life began here
• Atmosphere was CHAOTIC
• NO Oxygen early on
• 1st prokaryotes
Precambrian Time
• 2nd – Cyanobacteria
• Photosynthesis and oxygen -- ozone
• NOW life on earth surface
• 1 billion yrs ago
• Multicellular organisms
• eukaryotes
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
Paleozoic Era
• END of REPTILES and winged insects
• MASS EXTINCTION – 90% of water species are gone
Mesozoic Time
• 251 million – 185.5 million
• “Middle Life”
• Age of Reptiles– Dinosaurs– Birds– Conifers– Flowering Plants
Mesozoic Time
• EXTINCTION ??????????
Cenozoic Time
• 65 million – today
• Recent Life
• Age of Mammals– Mastodons– Saber toothed cats– Camels, sloths, small horses– Humans
Cenozoic Time
• ICE AGE
• Organisms moved to Equator to live or become extinct
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