1. Notes: Forces of the Earth

2. Who was the scientist who discovered the fact that the tectonic plates were moving? What evidence did he have? Was his theory supported or rejected? What force can cause the Earth’s tectonic plates to move?

3. Notes: Forces of the Earth
Alfred Wegener was the scientist who coined the term “Pangaea” and developed the theory of continental drift based on several pieces of evidence:
Land features – the continents’ shapes seem to fit together like a jigsaw puzzle.
Fossils – the same type and age of fossil were found on different continents. Some were found on South America, Africa, and Australia and nowhere else on Earth.

5. Notes: Forces of the Earth
Mountain ranges – mountain ranges in the U.S. match up with mountain ranges in Europe.

7. Notes: Forces of the Earth
4. Climate records – fossils and rock records show tropical plants on an island now in the Arctic ocean, and there are glacier scratches in South America.

11. Forces of the Earth
The scientific community reacted with disbelief and were almost hostile to this theory because Wegener could not explain HOW the continents could be broken up and moved apart. Because Wegener could not describe a force that would move something as big as a continent, his hypothesis was rejected.

12. Notes: Forces of the Earth
What can force continents to move?
In the Earth’s asthenosphere, the rock is soft like putty – warmer material rises and cools, while cooler material sinks.
CONVECTION
Convection occurs in the asthenosphere moving the tectonic plates across the surface of the Earth.

13. Notes: Forces of the Earth
What determines the direction of the tectonic plates? In areas where convection currents are moving downward, material from the lithosphere is pulled down into the Earth. In areas where the convection currents are moving upward, material from beneath the lithosphere is pushed upward.