1. Drifting Continents
Did Pangea Exist?

2. The Theory of Continental Drift
A German scientist named Alfred Wegener formed the hypothesis that the continents had moved!
He proposed that all the continents had once been joined together in a single landmass and have since drifted apart.
Wegener named this supercontinent Pangea.

3. The Theory of Continental Drift
Wegener’s idea that the continents slowly moved over the earth became known as continental drift.
Unfortunately Wegener could not provide a satisfactory explanation for the force that pushed or pull the continents. Therefore most geologists rejected his idea.

4. Evidence of Continental Drift
Evidence from landforms:
Mountain ranges and other features on the continents provided evidence for continental drift.
Mountain ranges in South Africa line up with mountain ranges in Argentina.

5. Evidence for Continental Drift
Evidence from fossils
A fossil is any trace of an ancient organism that has been preserved in rock.
Glossopteris fossils have been found in rocks in Africa, South America, Australia, India, and Antarctica.

6. Evidence for Continental Drift
Evidence from climate
Fossils of tropical plants have been found too far south to have survived.
Glacier deposits are found too far north to have existed.
These clues provide evidence that continental drift really happened.

7. Rejection!!
Even with the evidence, most scientists rejected Alfred Wegener’s theory for about a half a century, from the 1920s to the 1960s.

8. Convection Currents in the Mantle
Energy is constantly on the move!
The movement of energy from a warmer object to a cooler object is called heat transfer
There are three types of heat transfer: radiation, conduction, and convection.

9. Radiation Radiation is the transfer of energy through empty space.
Heat transfer by radiation takes place with no direct contact between a heat source and an object.

10. Conduction
Heat transfer by direct contact of particles is called conduction.
When your hand touches a metal spoon sitting in a boiling pot of soup, the heat from the bottom of the pot is transferred to your hand by conduction.

11. Convection
Convection is the transfer of heat by the movement of a heated fluid.
Convection deals with density.
Density is the measure of how much mass is there in a volume of a substance.

12. Convection
When a liquid or gas is heated, the particles move faster and the density decreases.
As the fluid becomes cooler, its density increases.
As density increases, the fluid sinks.
Heat Rises!!

13. Convection
The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.
Without heat, convection currents will eventually come to a stop.

14. Convection in the Earth’s Mantle
The heat source for these convection currents in the mantle comes from the heat of the Earth’s core.

15. Radiation, Conduction, and Convection