Table of Contents

Drifting Continents 5:1

Pg. 164-167

Sea-Floor Spreading 5:2

Pg. 168-173

The Theory of Plate Tectonics 5:3

Pg. 174-179

Plate Tectonics

Inside Our Planet

Drifting Continents 5:1

Alfred Wegener, a German scientist, hypothesized that all the continents were once joined together in a single landmass and have drifted apart.

Wegener called this single landmass, or supercontinent, Pangaea.

This theory became known as Continental Drift.

http://www.agci.org/classroom/geosphere/animations/pangea-

animation.php

Continental Drift

Drifting Continents 5:1

Wegener used evidence from:

* Land Features

* Fossils

* Climate

His hypothesis was rejected, however, because he could not explain HOW the continents moved to their present day location.

Sea-Floor Spreading 5:2

The mid-ocean ridge forms the longest chains of mountains in the world, rising up from the ocean floor.

Ocean FloorsMid-ocean ridges rise from the sea floor like stitches on the seams of a baseball.

The Sea-Floor is Spreading

Sea-Floor Spreading 5:2

Sea-floor spreading adds more crust to the ocean floor. At the same time, older strips of rock move outward from either side of the ridge.

Evidence for sea-floor spreading comes from:

•Pillow like lava rocks on the ocean floor

•Magnetic stripes follow similar patterns on either side of the ridge

•Ages of rocks are older further from the mid-ocean ridge

Sea-Floor Spreading 5:2

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches in a process called subduction.

http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_boundaries/en/index2.html?width=570&height=475&popup=true

The Theory of Plate Tectonics 5:3

The theory of plate tectonics states that Earth’s plates are in slow, constant motion driven by convection currents in the mantle.

Plate Tectonics

Plates meet at one of three types of plate boundaries:

• Divergent

• Convergent

• Transform

The Theory of Plate Tectonics 5:3

Ticket Out The Door

Use the index card corresponding with your number to create one question about Plate Tectonics that can be answered by another student.