Continental Drift

How many continents are there?

Were the continents always located in the same position? llege/geo/egeo/flash/2_1.swf m/books/earth_science/t erc/content/visualizatio ns/es0806/es0806page0 1.cfm?chapter_no=08 Drift animations

A continental puzzle

In 1912 a German meteorologist named Alfred Wegener noticed that the continents fit together like puzzle pieces. He proposed that the continents were joined together in the past, in a large land mass called Pangaea.

Over time, the continents drifted apart – Wegener named his theory “Continental Drift”.

He supported his theory with four pieces of evidence. 1. Puzzle like fit of continent edges

2. Matching fossils of plants and animals on once connected land areas. Fossils of Glossopteris are found in Permian rocks of South Africa, India, Australia, South America, and Antarctica

3. Rock similarities and ages Mountains in South America and Antarctica are believed to have formed as part of the same mountain chain.

4. Climate evidence (Glacial evidence in Africa, South America, Australia, and India and tropical plant fossils in Arctic areas) Fossils found in Antarctic soil indicate that the now frigid continent was once lush with trees and ferns, and home to dinosaurs, amphibians, and later, marsupials.

Wegener’s theory made sense, but no one wanted to accept it until they knew HOW the continents moved.

In the 1960’s, a Princeton University scientist named Harry Hess, discovered how the continents drifted. Continental Drift Whiplash

Seafloor Spreading Magma in the mantel rises and pushes the plates apart, forming new oceanic crust.

Seafloor Spreading causes Continental Drift

Supporting evidence of seafloor spreading 1. Magnetic iron particles record the time of the rock formation Rocks farther away from the opening age at the same rate on both sides.

A map of the ocean floor provides even more evidence

Iceland shows seafloor spreading above the water, which makes it easier to study

Plate Tectonic Theory Theory of Plate Tectonics -Earth’s crust is broken into plates which float and move.

Earth’s crust made of many plates is similar to the panels on the outside of a soccer ball.

There are about 13 plates covering Earth’s surface

Plate Boundaries (edges) When the plates move, their boundaries, or edges, can scrape and collide.

Convergent Boundary Plates move toward each other

Convergent Boundary When two continental plates move into each other, the plates combine and form mountains. (India into Asia)

Convergent Boundary When an oceanic plate runs into a continental plate, the heavier oceanic plate subducts (sinks) back into the mantle. Volcanic mountains are created along this edge.

Oceanic plate into continental Example: Pacific plate (oceanic) subducts (sinks) under Japan (continental).

Divergent Boundary Plates move apart

When both diverging plates are both oceanic, it is called seafloor spreading (Mid-Atlantic Ridge)

When both diverging plates are continental it is called rift valley formation (Africa) hill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/ /30425/19_21.swf::Fig.% % 20-%20Evolution%20of%20a%20Divergent%20Plate%20Boundary

Transform Boundary Plates slide past each other

San Andreas Fault

San Andreas Fault, CA Each time the plates slide past each other, an earthquake occurs

Find the three boundaries

Asthenosphere A plastic-like layer found below the lithosphere. The rigid oceanic and continental plates of the lithosphere sit on top

The Asthenosphere is heated by the hot Outer Core

Convection Current Hot material rises, cooler material sinks, creating a current, called a Convection Current core mantle crust

When the asthenosphere moves, it carries the lithospheric plates (divergent, convergent, and transform motions) Convection currents cause plate motion

Every time these plates move we get earthquakes, volcanic eruptions, and possibly tsunamis