The Earth

1. The Earth Francesca D’Argenio

2. The Theory of Plate Tectonics • Developed mid 20th Century • Alfred Wegener, German geologist. • His “TheoriederKontinentalverschiebung” (continental drift) was based on the form of continents and fossils, but lacked explanation for motor of drift and a single impressive circumstantial evidence. • Over decades the pieces of evidence he had were pieced together using the discovery of the sea-floor spreading.

3. Evidence • The first evidence that the plates did move, contrary to the belief of the majority, was the discovery of variable magnetic field in rocks of different ages. • Initially this was explained as the global crust expanding, however later collaborations developed the theory of plate tectonics, but avoided the need for an expanding globe by accounting for new oceanic crust with the crust destroyed at destructive and passive boundaries.

4. Boundaries ^_^ • Divergent: • Convergent: At divergent boundaries the plates move apart. The magma wells up and cools as it meets the icy ocean, forming new plate material. The heavy oceanic plate pushes underneath the lighter, more porous continental plate, destroying the material. This is called a seduction zone. (subduction) When two continental plates come together, they push up against each other, forming mountains which resemble the folds in material, hence why they are called fold mountains. HOT STUFF!!!

5. Volcanoes • Shield and Composite. • Shield: broad, gently sloping volcano with more runny lava. • Composite: steep, viscous lava.