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10.3 The Changing Continents
Transcript of 10.3 The Changing Continents
The Changing Continents
Shaping Earth's Crust
Slow movements of plate change the size and shape of the continents over millions of years.
All the continents that exist today contain cratons.
- large areas of stable rock that are older than 540 million years.
Rocks within cratons that have been exposed at Earth's surface are called
Effects of Continental Change
Modern climates are a result of past movements of plates.
When continents move, the flow of air and moisture around the globe changes.
Changes in Climate
Geologic evidence shows that ice once covered most of Earth's continental surfaces.
Much of the ice sheets melted as continents drifted.
The Supercontinent Cycle
The Supercontinent Cycle - the process by which supercontinents form and break up over millions of years.
Rifting and Continental Breakup
One way that continents change shape is by breaking apart (
Rifting can occur on both oceanic and continental crust.
Terranes and Continental Growth
Continents can also change by gaining material.
Most continents contain cratons surrounded by terranes.
- a piece of lithosphere that has a unique geologic history.
May be part of a large piece of lithsophere.
Changes in Life
Populations of organisms get separated when mountains for rifts form.
New species may evolve after separation.
Why Supercontinents Form
Formation of Pangaea
Breakup of Pangaea
The Modern Continents
The Geography of the Future
Convergent plate boundaries cause continents to collide.
Neither continent suducts, the plate boundary eventually becomes inactive.
Over time, all continents collide to form a supercontinent.
Pangaea - the supercontinent that formed 300 mya.
Began to break up 200 mya.
The Appalachian Mountains formed during the collisions that created Pangaea.
Panthalassa - a single, large ocean that covered Earth's surface during the time of Pangaea.
About 200 mya, Pangaea began to break apart.
Laurasia and Gondwanaland
Laurasia drifted northward and broke up into N. America and Eurasia.
Gondwanaland broke into two parts.
One became S. America and Africa.
The other became India, Australia, and Antarctica.
As plates move, Earth's geography will change dramatically.
Scientists predict that in 250 million years, the continents will come together again to form a new supercontinent.
As the continents drifted, they collided with tarranes and other continents.
Mountains such as the Rocky Mountains formed.
Late motion also caused new oceans to open up and others to close.
When a plate carrying a terrane subducts another a plate made of continental crust, the terrane is scraped off.
- when a terrane becomes a part of the continent.
Major mountain chains can form this way.
Los Angeles will move north and eventually be located
of San Francisco.
In ~150 million years.