Plate Tectonic Theory

TXT pg. 106Chapter 3…section 5

Definitions to know

• Plates: Sections of the lithosphere that are fitted together along cracks

• Scientific Theory: Well tested concept that explains observations

Theory

• Pieces of the earth’s lithosphare are in slow, constant motion, driven by convection currents in the mantle.

• Explains the formation, movement, and subduction of Earth’s plates.

HOW DO THEY MOVE???

• Movements in the mantle cause the plate to move

• Gravity pulls one side of the plate down by subduction, causing the rest of the plate to move forward

• As they move, the collide, pull apart, or grind with other plates

• This causes the formation of volcanoes, mountain ranges, and deep ocean trenches

Plate Boundaries

• Extend into the lithosphere

• Faults: (Form along the boundaires)Break in the earth’s crust where rocks have slipped past each other

• 3 Kinds:– Divergent– Convergent– Transform

Divergent Boundaries

• Plates move apart (Diverge)

• Most occur on mid ocean ridges

• Can occur on land Causing a Rift valley (deep valley where the plates slide apart

• Example: Death Valley

Convergent Boundaries

• Where 2 plates come together

• When they converge, they will collide. Density decides which one gets forced up and which one down….More dense plate sinks under other past

• Oceanic Crust is more dense than continental crust

• When continental crust collides, neither is more dense, so mountain ranges form.

Transform Boundary

• 2 plates slide past each other in opposite directions (Like rubbing your hands together)

• Crust is not created or destroyed here

• Earthquakes happen at transform boundaries

Pangea Proof

• By proving that the earth’s plates are moving, scientists were able to show that there was once a pangea and that the continents broke apart and moved to their current position.

• Pg. 110 shows this in motion and the time span