MondayNovember 1, 2010

(Continental Drift and Plate Tectonics)

The Launch PadMonday, 11/1/10

Why do modern birds show more of a similarity to

modern reptiles than

modern mammals show to modern reptiles?Birds branched off from reptiles much later

than mammals did, thus retaining more of a similarity.

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We will have a test this Friday.

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Continental DriftAn Idea Before Its Time

German scientist Alfred Wegener first proposed the continental drift

hypothesis in 1915. His work was published as “The

Origin of Continents and Oceans.” The continental drift hypothesis

states that a supercontinent called Pangaea began breaking apart about

200 million years ago. The continents “drifted” to their

present positions. Continents “broke” through the

ocean crust.

Antonio Snider-Pellegrini (1858)

Alfred Wegener’s Pangaea

Pangaea approximately 200 million years ago

Figure 7.2

Continental Drift

Evidence Cited by Wegener

• Fit of South America and Africa

Continental Drift

Evidence Cited by Wegener • Fossils match across the

seas

Continental Drift

Evidence Cited by Wegener • Fossils match across the seas

Continental Drift

Evidence Cited by Wegener • Fossils match across the seas

Continental Drift

Evidence Cited by Wegener • Rock types and structures

Similar mountain ranges on different continents

Figure 7.7

Continental Drift

Evidence Cited by Wegener • Ancient climates –

climates evidence matches on present-day continents.

Figure 7.A The Breakup

of Pangaea

Continental DriftAn Idea Before Its Time

The main objection to Wegener’s proposal was the inability to

find a mechanism for continental drift.

The Continental Drift Mechanism Discovered: Plate TectonicsThe concept of plate tectonics is

more encompassing than the idea of continental drift.

Plate tectonics is associated with Earth’s rigid outer shell, called the

lithosphere. Earth’s lithosphere consists of

several “plates”, which are moving very slowly across the mobile

asthenosphere below.The largest of these plates is the

Pacific plate. The plates are mostly beneath the

ocean.

The Earth’s asthenosphere lies just beneath the

lithosphere. The asthenosphere is

hotter and weaker than the lithosphere.

This allows for the motion of the lithosphere over

the asthenosphere

Plate Tectonics

All major interactions among plates occur along their boundaries.

Plate Tectonics

Figure 12.6

GEODe Earth Science

Plate TectonicsSlides 698-725