Continental Drift and Plate Tectonics How the Earth’s Crust Changes

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Alfred Wegener’s Discovery What did Alfred Wegener discover? Looking at a map, he decided that the continents seemed to fit together and at one time, they must have been together. He called his super continent “Pangaea” Came up with the theory of Continental Drift.

EVIDENCE FOR CONTINENTAL DRIFT What evidence was there for continental drift? The continents fit together like a puzzle. Mesosaurus fossils were found on N. America, S. America, and Africa Glossopteris pollen was found on almost every continent.

EVIDENCE FOR CONTINENTAL DRIFT What evidence was there for continental drift? The mountains of Europe and N. America were formed at the same time and made of the same material. Diamonds in South America and Africa are the same type and the same age

PLATE TECTONICS What is plate tectonics? How do the plates move? Plate tectonics is Alfred’s theory taken a step further. All of the lithosphere (crust) is divided into plates that move. Convection in the mantle

CONVECTION What is convection Convection is a process of heat transfer. Warm magma rises from the bottom of the mantle, and cooler magma sinks in a circular motion The crust must move due to the motion.

PLATE BOUNDARIES What are plate boundaries? What types of plate boundaries are there? Places where the plates of the crust meet. Divergent Convergent Transform

DIVERGENT What is a divergent plate boundary. It is where two plates are moving apart to create new crust. Divergent boundaries are also known as spreading centers or rift valleys The mid Atlantic Ridge is the largest. New crust is created.

CONVERGENT PLATE BOUNDARIES What is a convergent plate boundary? It is where two plates are moving together. There are three types: 1. Ocean/Ocean; denser one sinks into subduction zone 2. Ocean/Continent; ocean plate will sink into subduction zone

SUBDUCTION ZONES What is a subduction zone? A place where the crust goes back down into the mantle to remelt These are also known as trenches Volcanoes are made on the upper plate of the subduction zone.

CONVERGENT PLATE BOUNDARIES What is a convergent plate boundary? The third type of convergent plate boundary is continent- continent collision. Two continents hit, crash and make mountains

Continent Collision

TRANSFORM PLATE BOUNDARY What is a transform plate boundary Where two plates move past each other. The famous transform plate boundary is the San Andreas fault in California.