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