Plate Tectonics

Alfred Wegener Proposed the Theory of Continental Drift Evidence to support his theory Fossils of the same plants and animals on South America, Africa and Antarctica Continents of South America and Africa fit together like a puzzle Coal Beds in the Appalachian Mountains line up with Coal beds in Great Britain

Harry Hess Proposed the Theory of Sea-floor Spreading In the middle of the oceans, magma rises and pushes the continents out away from the mid- ocean ridge The scientific community questioned why the Earth’s diameter wasn’t getting larger? What was driving the rising magma in one region?

Convection currents During WWII, studies were done of the ocean floor to lay telegraph line to Europe so we could communicate with troops. Studies were done to find oil, much of which was known to be in ocean beds The first sonar was used to map the ocean floor and much was explained about the movement of the plates Subduction zones were the explanation of the recycling of the plates

Divergent Boundaries Plates move apart Land Features: Mid-Ocean Ridges Shallow earthquakes Magnetic striping Newest crust on Earth Rift Valley Crater Volcanoes Mid-Atlantic Ridge Iceland East African Rift Valley

Transform Boundaries Plates slip past each other Land features: Fault lines Frequent earthquakes Shallow earthquakes San Andreas Fault

Convergent Boundaries Plates move toward each other Oceanic plates are denser than continental plates Denser plates sink below less dense plates – this is called subduction and subduction zones Three types Continental vs. continental Continental vs. oceanic Oceanic vs. oceanic

Convergent Boundaries Continental vs Continental plates push into each other and push up Crust gets thicker Neither plate subducts Deep earthquakes Himalayas are formed this way – they are still getting bigger

Convergent Boundaries Continental vs Oceanic Oceanic plate is denser and subducts Where the plates meet they push each other down creating an ocean trench Where the plate dives back into the mantle it melts and forces its way back to the surface creating a volcanic mountain range near the coast Very deep earthquakes Andes Mountains Cascade Mountains

Convergent Boundaries Oceanic vs Oceanic One plate subducts – the older is denser Crust material forces it’s way back to the surface and forms underwater volcanoes Once they break the surface you get a volcanic island arc Deepest ocean trenches Mariana Trench Japan Aleutian Islands