Continental Drift Theory and Plate Tectonics

Continental Drift Theory

• Proposed in 1912 by ___________?

• Theory - 200 million years ago the Earth was one giant continent called _______________?

• From this one continent today's continents broke apart and drifted into their current locations.

• How did Wegener support his theory?

Support For Continental Drift Theory

• The Shapes Match

• The continents look as if they were pieces of a giant jigsaw puzzle

• The Plants and Animals Match

• Identical fossil species along the coastal parts of Africa and South America.

• Rocks Match - These broad belts match when the end of the continents are joined.

Clues from the Ocean on Continental Drift

• According to scientists, how does lava get to the ocean floor?

• How do scientists explain why ocean floor is older farther away from the mid ocean ridge?

Why Few People Believed

• It was difficult to conceive that large continents could plow through the sea floor to move to new locations.

• What kind of forces could be strong enough to move such large masses of solid rock over such great distances?

Theory of Plate Tectonics

• The theory of plate tectonics states that the Earth's outer shell is not one solid sheet of rock but a series of large and small moving plates.

• What did scientists realize when they “connected the dots?”

What is a Tectonic Plate?

• A tectonic plate is a massive, irregularly shaped slab of solid rock.

• Plate size can vary greatly, from a few hundred to thousands of kilometers across

How do the Plates Move?

• No one knows for sure but most think that the plate driving force is the slow movement of hot, softened mantle that lies below the rigid plates (CONVECTION)

Plate Boundaries

Types of Plate Boundaries

• Divergent (Spreading) Plate Boundaries – Oceanic

• Divergent (Spreading) Plate Boundaries –Continental

• Convergent Plates– Subduction: Continental and Oceanic– Subduction: Oceanic– Continental

• Transform (Faulting) Boundaries

In Conclusion….

• How does the theory of Plate Tectonics affect us?