1. Plate Tectonics

2. Aim: How does the Theory of Plate Tectonics influence the way the Earth is today?
I. Plate Tectonics
A. Theory of Plate Tectonics
1. The surface of the Earth is composed of about a dozen major rigid, moving crustal plates and several smaller plates

4. Plates
a. Slabs of Earth’s lithosphere (crust and upper mantle)
b. Average thickness is 100 km (62 miles)
c. Most plates support both continent and ocean
B. Continental Drift – states that the continents have drifted and still are drifting apart.

6. C. Why do the plates move?
Due to tremendous heat, rock in the asthenosphere is like hot taffy
This allows plates to ride on top of hot, flowing rock.
3. Plates move because heat is being released from deep inside the earth.
4. Convection currents causes hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge).

8. Alfred Wegener

9. D. Alfred Wegener – proposed that in the distant past, the Earth’s continents were all joined as a single landmass.
1. Evidence for his theory
South America and Africa would fit remarkably well, shoreline to shoreline.
If the Americas were moved next to Africa and Europe, there would be a match of ancient continental rocks and tectonic (fold and fault) structures.
c. Pangaea – when Wegener placed all the continents together like a puzzle, it formed a large landmass which he called Pangaea.

10. Fossil Evidence

12. GIF image 240x180 pixels
Animated Plate Tectonic Reconstruction