Download - Slide 1 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