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History of Current Life on Earth. Theories and Ideas on What Has Happened Since Life Began. Modern Life. Modern Life. Cambrian Explosion ~ 500 mya All modern animal phyla appear in fossil record First records of modern animal life Five catastrophes = Five mass extinctions.

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History of Current Life on Earth

Theories and Ideas on What Has Happened Since Life Began



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Modern Life

  • Cambrian Explosion

    • ~ 500 mya

    • All modern animal phyla appear in fossil record

    • First records of modern animal life

  • Five catastrophes = Five mass extinctions



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Ordovician-Sulurian Extinction

  • Occurred ~450 mya

  • Caused by glaciation

  • Dominant animals were marine

    • More than 25% of marine families went extinct



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Late Devonian Extinction

  • ~380 mya

  • Caused by cooling temperatures and a possible meteorite impact

  • Prior to extinction the dominant animals were reef builders.

    • About 22% of marine families perished



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Permian-Triassic Extinction

  • ~250 mya

  • Worst mass extinction

    • Up to 95% of all species on Earth suddenly became extinct

    • Reason unknown, believed that the ocean levels may have dropped



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End Triassic Extinction

  • ~200 mya

    • Most likely caused by massive floods of lava erupting from the central Atlantic

    • Up to 22% of marine families

    • Vertebrate deaths unknown



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Cretaceous-Tertiary Extinction

  • ~65 mya

  • Cretaceous period lasted 150 million years

  • Extinction mostly likely caused by giant asteroid hit off of Mexico

    • 16% of marine families went extinct

    • 18% of vertebrates went extinct



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Fossil Record

  • Fossil record

    • Remains of a once living organism

    • Bones, molds, casts, footprints

  • Can be dated

    • Relative Dating

      • Estimates the age of events and fossils using basic stratigraphic rules

      • Provides a sequence of age

    • Absolute Dating

      • Based on the physical or chemical properties of the materials artifacts and fossils

      • Provides a numerical age



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Lucy

  • Discovered by a team working in Ethiopia with Donald Johanson

  • 40% of a skeleton of a member of Australopithecus afarensis

  • About 3.2 million years old

  • Small brain capacity (like apes) but walked bipedal (like hominids)



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Human Evolution

  • One current model looking at human evolution and where it occurred

  • Homo refers to human

  • Different species existed and were relations to each other, but did not necessarily give direct rise to each other

  • Many other hominines exist and most likely were common ancestors of those in the genus Homo


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