1. Continental Drift & Plate Tectonics

2. Theory of Continental Drift
Continents moved horizontally over time to current location
On the bottom of the website - convection-plate-tectonics-earthquakes--volcanoes.html

3. What evidence is there for this theory?
PANGAEA ( mya)
Alfred Wegener studied the shape and positions of the continents (looked like puzzle pieces)
In 1912, he proposed that the continents were once joined together = Pangaea
Believed that “super-continent” split apart and each continent drifted to its present location

4. What evidence is there for this theory?
FOSSILS
Plant and animal fossils found on the coastlines of different continents
Mesosaurus fossils found in South America and Africa
Mesosaurus was a fresh water and land animal
**Lands must have been connected at some time in the past**

5. What evidence is there for this theory?
FOSSILS (cont.) (not on note sheet)
Glossopteris fossils found in Africa, Australia, India, South America, and Antarctica
Glossopteris fern found in wide variety of modern climates
**Lands must have been connected at some time in the past**

6. What evidence is there for this theory?
CLIMATE
Warm weather plant fossils on an island in the Arctic Ocean
Glacial deposits and grooves in southern areas of South America, Africa, India, and Australia
**Lands must have been connected and either drifted from tropical areas or from ice covered regions**

7. What evidence is there for this theory?
ROCKS
Similar rock structures found on different continents

8. Problems with the Theory of Continental Drift
No mechanism for movement of continents
He theorized that they moved but he couldn’t explain how
Wind and currents could possibly move continents
what caused them to move?
Theory was not accepted by scientists
Needed more evidence and information

9. Brain Pop

10. Plate Tectonics Part II

11. Theory of Plate Tectonics
Combined continental drift and sea floor spreading
States…Earth’s crust and upper mantle are broken into sections called plates
Plates move around the mantle (Like rafts that float on water)

12. Major Plates on Earth

13. Tectonic Plates 100km thick and less dense than the material under it
Composed of crust and upper mantle - lithosphere
100km thick and less dense than the material under it
Asthenosphere – the layer below the lithosphere
This is the material that the plates “float on”
jello like consistency

14. What causes the plates to move and the sea floor to spread?
Why do the plates move?
What causes the plates to move and the sea floor to spread?
Convection Currents!
Difference in densities cause the hot asthenosphere to be forced toward the surface
When it reaches the surface, it moves horizontally and carries plates with it
Cools, becomes denser and sinks into the mantle taking overlaying crust with it

15. Convection Currents in the Mantle
Animation:

16. Convection Currents