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 warmer object to a cooler object is called a 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 hands touches a metal spoon sitting in a boiling pot of soup, the heat from the bottom of the pot is transferred to you hand by conduction.

11. Conduction

12. 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.

13. 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!!

14. 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.

15. 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.

16. Radiation, Conduction, and Convection