Three ways tectonic plates interact: Converge (collide) Diverge (move apart) Slide past one another (“Transform Boundary”)

What’s Inside the Earth?

2 types: Ocean and Continental Crust OCEAN crust Denser Thinner Eventually subducted Relatively young CONTINENTAL crust Less dense Thicker Rarely/never subducted Oldest crust on Earth

1912- Theory of Continental Drift Continents were formed from the drifting apart of one super continent: Pangaea Alfred Wegener

Theory of Continental Drift The shape of continents seemed to “fit” together

Found evidence of similar fossils and geological formations on different continents

Geologic Evidence Big flaw with this theory: How did the continents actually move?

Seafloor Spreading In 1962, Hess proposed seafloor spreading as the mechanism for continents to actually drift. Hess proposed that new ocean crust was being created along the Mid Ocean Ridges. As ocean crust collided with other plates, it was subducted and thus destroyed and recycled.

Theory of Plate Tectonics Outer “shell” of Earth is broken into plates Plates are carried by convection cells in mantle Moving plates collide, diverge, or slide by each other

https://youtu.be/kwfNGatxUJI

Convection cells in (upper mantle) cause sea floor spreading

Convergent Boundaries 1. Continental/Oceanic Denser ocean crust is subducted (pulled) under Deep trenches, mountains, strong earthquakes Melting oceanic plates turn into magma http://education.sdsc.edu/optiputer/flash/subduction_5.htm Examples: Andes Mts. Cascade Mts.

Convergent Boundaries 2. Oceanic/Oceanic Slower plate is subducted (pulled under) Outcome = volcanic islands, strong earthquakes, tsunamis, deep trenches Ex: Aleutian islands (Alaska), Japan, Southeast Asia http://education.sdsc.edu/optiputer/flash/convergance2.htm

Convergent Boundaries 3. Continental/Continental Continental Crust is light, so no subduction Instead, piles of crumpled, folded crust = tall mountains Examples: Himalayan Mts., Appalachian Mts., Alps

Himalayan Formation http://www.edumedia-sciences.com/en/a823-formation-of-the-himalayas

Divergent Boundary Normal Fault Mostly below the ocean Sea Floor Spreading - Forms new crust http://education.sdsc.edu/optiputer/flash/seafloorspread.htm Example: Mid Atlantic Ridge, Rift Valley in Africa

Great Rift Valley- Africa

Age of Seafloor: Red is newest, green oldest

Transform Plate Boundaries 2 plates sliding in opposite directions E.g. San Andreas Fault http://education.sdsc.edu/optiputer/flash/SanAndreas.htm

Major Tectonic Plates