Plate Tectonics

L.O: To understand how tectonic plates move and the theory of continental

drift.

http://www.bbc.co.uk/news/world-asia-pacific-12709598

Boxing Day Tsunami – 2004. Can you explain what caused it?

http://news.bbc.co.uk/1/hi/world/4136289.stm

http://www.youtube.com/watch?v=T1-cES1Ekto

An old theory about the continents and surface of the

earth• Mountains, continents and volcanoes were formed

as a result of the shrinking of the crust as the earth cooled. A bit like cooling custard

• Earthquakes were an action of God.

Wegener’s hypothesis on continental drift

The coastlines of South America and Africa look like they used to fit together, over time all of the

continents have moved apart

Alfred Wegener

Try to make the jigsaw by joining the continents together. What other evidence is there that the continents used to be joined up?

Tectonic theoryPeople once thought that the oceans and the continents were formed by shrinkage from when the Earth cooled down after being formed.

Alfred Wegener proposed something different. People didn’t believe him because he couldn’t prove it, so he had to find some evidence:

These continents look like they “fit” together. They also have similar rock patterns and fossil records. These are the two pieces of evidence that led me to believe that there was once a single land mass. This

is my TECTONIC THEORY.

Wegener had trouble convincing people his theory.

Impossible! continents can’t move the force needed would be so big it would stop the earth rotating. They have the same fossils because there must have

once been land bridges that joined them. The land bridges must have

been flooded over time.

The continents fit together and have similar fossils; they must have once been joined. Perhaps they moved

apart because of tidal forces and the earths rotation.

Sort out the other scientists opinions into for and against Wegener’s theory

The Answer:

1) Scientists discovered 50 years later that the Earth generates massive amounts of heat through radioactive decay in the core. This heat generated convection currents in the mantle causing the crust to move

2) We also now know that the sea floor is spreading outwards from plate boundaries

Tectonic theoryThe Evidence:

1) Some continents look like they used to “fit” together

2) Similar rock patterns and fossil records

The Problems:

Wegener couldn't explain how continental drift happened so nobody believed him

Conclusion – scientists now believe Wegener’s Tectonic Theory

Continental Drift

Crossword