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Drifting Continents. Did Pangea Exist?. 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.
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Drifting Continents Did Pangea Exist?
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.
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.
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.
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.
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.
Rejection!! Even with the evidence, most scientists rejected Alfred Wegener’s theory for about a half a century, from the 1920s to the 1960s.
Convection Currents in the Mantle • https://www.youtube.com/watch?v=Kpoko_l34ZE WATCH VIDEO • 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.
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.
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.
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.
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!!
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.
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.
