Plate Tectonics

The theory of Continental Drift explained the following pieces of evidence: matching coastline shapes, the same fossils on different continents, tropical plants found in cold climates. The theory of Plate Tectonics explains the formation, movement and subduction of the Earth’s plates.

The Earth’s lithosphere is made of a number of different plates moving in a variety of directions. How the plates move relative to each other determines the type of boundary and the type of stress. There are 3 types of boundaries and stress are:

Divergent Boundaries= Tension At divergent boundaries the plates are moving apart. As the crust splits new crust is formed from magma moving up from below.

Evidence of Sea-Floor Spreading Type of Rock found here is called “Basalt” which is made from Lava. Age of Rock gets older as distance from Rift increases. Magnetic Alignment of Iron Particles is like a “mirror” on each side of Rift. Thermal Heat Vents exist here.

Divergent Boundaries These often form rift valleys.

Transform Boundaries= Shearing In Transform boundaries the two plates slide past each other (Pacific & North American Plate). Usually find many earthquakes along these boundaries.

Convergent Boundaries= Compression Convergent Boundaries are formed when two plates collide. One, or both, of the plates is subducted depending on the type of crust.

Convergent Boundaries If dense ocean crust meets light continental crust the ocean crust usually subducts. The resulting friction often causes deep earthquakes and chains of volcanic mountains along the edge of continents. Ocean trenches are also created here.

Subduction Subduction is when crust material is forced back down into the mantel.

Convergent Boundaries

Convergent Boundaries Ocean crust colliding with ocean crust can cause one of the plates to subduct. The friction can cause volcanic island arcs in the ocean.

Convergent Boundaries

Convergent Boundaries When continental crust meets continental crust light continental crust layers buckle up. This forms interior mountain regions that grow taller every year.

Convergent Boundaries

Convergent Boundaries

http://www.youtube.com/watch?v=HrKTuCDierM