Plate Tectonics

Alfred Wegener

German geologist 100 years ago

Noticed the continents looked like a jigsaw puzzle

He thought millions of years ago Earth’s continents were joined together

Continental Drift Theory http://www.eduplace.

com/kids/socsci/ca/books/bkf3/imaps/AC_01_005_drift/AC_01_005_drift.html

Evidence for Continental Drift Mountains on

east coast of South America are the same rocks as mountains on west coast of Africa

Rocks are the same age

Evidence for Continental Drift

Fossils were found of a freshwater reptile Mesosauras have been found in old rocks in South America and Africa

That animal couldn’t swim across the ocean, so the land must have been connected

Evidence- ocean floor spreading

The ocean between South America and Africa spreads 4 centimeters every year.

This matches the Continental Drift Theory- 130 million years X 4 cm = 520,000,000 cm

This is the width of the South Atlantic Ocean

Plate Tectonics

When Wegener thought of his theory, he didn’t understand how the Earth’s crust could move around.

Earth’s continents sit on plates of solid rock The asthenosphere (almost melted rock) acts as

a slippery surface the plates move around on

Plate Tectonics- Ocean spreading

Magma pushes up and forms new land

Causes tension (push/pull) on plate

Push causes the ocean floor apart and separates plates on either side of the mid-ocean ridge

Plate Tectonics- mountain building

Fold mountains Compression = squeeze/pushing

together Example: Himalayan mountains

Plate Tectonics- mountain building

Fault-block mountains One plate rubs past each other causes a shear

(force that twists, tears, pushes past each other) Example: Grand Teton Mountain Range