Plate Tectonic Theory TXT pg. 106 Chapter 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