Slide 1 History of Current Life on Earth Theories and Ideas on What Has Happened Since Life Began

Slide 2 Modern Life

Slide 3 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

Slide 4 Ordovician-Silurian Extinction

Slide 5 Ordovician-Sulurian Extinction Occurred ~450 mya Caused by glaciation Dominant animals were marine –More than 25% of marine families went extinct

Slide 6 Late Devonian Extinction

Slide 7 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

Slide 8 Permian-Triassic Extinction

Slide 9 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

Slide 10 End Triassic Extinction

Slide 11 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

Slide 12 Cretaceous-Tertiary Extinction

Slide 13 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

Slide 14 Fossil Record

Slide 15 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

Slide 16 Lucy

Slide 17 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)

Slide 18 Human Evolution

Slide 19 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