The History of Life on Earth

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Plate

Cocos Plate

Caribbean

Plate

Arabian

Plate

African

Plate

Scotia Plate

North

American

Plate

South

American

Plate

Antarctic

Plate

Australian

Plate

Philippine

Plate

Indian

Plate

Eurasian Plate

Slide 38

Consequences of Continental Drift

Formation of the supercontinent Pangaea about 250 million years ago had many effects:

A reduction in shallow water habitat

A colder and drier climate inland

Changes in climate as continents moved toward and away from the poles

Changes in ocean circulation patterns leading to global cooling.

Slide 39

History of Continental Drift

South

America

Pangaea

Millions of years ago

65.5

135

Mesozoic

251

Paleozoic

Gondwana

Laurasia

Eurasia

India

Africa

Antarctica

Australia

North America

Madagascar

Cenozoic

Present

Slide 40

The break-up of Pangaea lead to allopatric speciation.

The current distribution of fossils reflects the movement of continental drift. Similarity of fossils in parts of South America and Africa supports the idea that these continents were formerly attached.

The fossil record shows that most species that have ever lived are now extinct.

At times, the rate of extinction has increased dramatically and caused a mass extinction.

In each of the five mass extinction events, more than 50% of Earth’s species became extinct.

Slide 41

Five Big Mass Extinctions

Total extinction rate

(families per million years):

Time (millions of years ago)

Number of families:

Cenozoic

Mesozoic

Paleozoic

E

O

S

D

C

P

Tr

J

542

0

488

444

416

359

299

251

200

145

Era

Period

5

C

P

N

65.5

0

0

200

100

300

400

500

600

700

800

15

10

20

Slide 42

The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras.

This mass extinction caused the extinction of about 96% of marine animal species and might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen.

The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic.

Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs.

Slide 43