Theory Of Plate Tectonics

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J. Tuzo Wilson

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Canadian Scientist

Observed cracks in the continental crust similar to those on the ocean floor.

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Plates

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A section of the lithosphere that slowly moves of continental and oceanic crust

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Theory of Plate Tectonics

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Explains the formation, movement and subduction of Earth's crust
Plates carry the ???, parts of the ocean floor, or both

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Scientific Theory

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Well tested concept that explains a wide range of observations

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Plate Tectonics

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Theory that pieces of Earth's crust are in constant, slow motion, driven by convection currents in the mantle.

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Convection Currents

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The movement of a fluid, caused by difference in temperatures, transfers heat from one part of the fluid to another.

Geologists believe this causes plate movement.

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How can Earth's plates move?

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The plates of the lithosphere float on the top of the asthenosphere

As plates move, they collide, pull apart, or grind past each other, producing changes in the Earth's surface (mountains, volcanoes, deep ocean trenches, and earthquakes)

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Plates that include only ocean floor

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Pacific Plate
Nazca Plate

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Plates that include both continents and ocean floor

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All other plates (other than Pacific & Nazca)

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What would happen if the plates continue to move?

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They will collide & form mountains

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Faults

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A break in the Earth's crust where slabs of rock slip past each other

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3 types of plate boundaries

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1. Transform
2. Divergent
3. Convergent

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Transform Boundary

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Where two plates move past each other in opposite direction

Earthquakes form at this boundary

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Divergent Boundary

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Where two plates move away from each other

Most occur in the ocean - Mid Ocean Ridge

Occur on land - Rift Valleys

Example - Great Rift Valley - South Africa

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Convergent Boundary

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Where two plates move toward each other

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Rift Valley

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A deep valley that forms where two continental plates slide apart

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Deep-Ocean Trench

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A deep valley along the ocean floor through which oceanic crust slowly sinks back towards the mantle

Caused by the collision between oceanic plates

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Subduction

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The process by which oceanic crust sinks through a deep-ocean trench and back into the mantle

(more dence plates dive back into the mantle)

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Mid-Ocean Ridge

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The undersea mountain chain where new ocean floor is produced; a divergent plate boundary

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Volcanic Eruptions

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Caused by the collision between oceanic plates and continental plates

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Mountain Ranges

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Caused when plates carrying continental crust collide

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Continents' Slow Dance

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Plates move at a rate of between 1 and 10 centimeters per year.