Plate Tectonics and Continental Drift

Tectonic plates

large, solid pieces of the Earth’s lithosphere that are continuously moving in different directions atop the asthenosphere

Did you know?

All of the Earth’s crust – even the bottom of the oceans – are sitting on tectonic plates.

Did you know?

There are about seven major tectonic plates, and several minor plates.

We are on the North American plate.

Pangaea

A large, ancient supercontinent, composed of all continents joined together

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Pangaea broke up in stages, first breaking into smaller supercontinents including:LaurasiaGondwanaland

Convergent boundary

boundary between two tectonic plates that are moving toward each other

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Volcanoes are common along convergent boundaries.

A circle of volcanic zones called the Ring of Fire surrounds the Pacific Plate on converging boundaries.

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Convergent boundaries are DESTRUCTIVE because old crust at plate edges is destroyed and recycled as they come together.

Divergent boundary

boundary between two tectonic plates that are moving away from each other

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Divergent boundaries are CONSTRUCTIVE because this is where we find Earth’s youngest crust.

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There is a HUGE divergent boundary running down he middle of the ocean floor in the Atlantic Ocean.

Transform boundary

boundary where two tectonic plates slide past each other horizontally

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Transform boundaries are commonly active earthquake zones.

Southern California has about 10,000 earthquakes each year (most too small to feel).

Theory

A possible explanation that is supported by a large amount of evidence

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The Theory of Continental Drift proposed by Alfred Wegner only dates back to about 1912.

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Fossils of the same species of plants and animals can be found on different continents.

Convection currents

circular movement of heating, rising, cooling, and sinking molten material in Earth's mantle transfers heat that results in the movement of tectonic plates

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You can also find convection currents inThe airThe oceansLava lamps

Subduction zone

A convergent boundary where one tectonic plate slides under another tectonic plate

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Subduction zones often produce volcano chains offshore or along the coast of a continent.Example: Ring of

Fire around the Pacific Ocean - including the west coast of the US

Sea Floor Spreading

Hess's theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge

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Sea floor spreading happens at ocean floor divergent boundaries.

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Sea floor spreading happens at a rate of about 5 cm each year.

Continental Drift

Wegner's hypothesis that all continents were once connected in a large, single landmass that broke apart about 200 million years ago and drifted slowly to their current positions

Did you know?

In the future, another supercontinent may form as continents run into each other again.

(millions of years from now)

Earth’s Future Supercontinent???