Drifting ContinentsDrifting ContinentsDid Pangaea Exist?Did Pangaea Exist?

The Theory of Continental DriftThe Theory of Continental Drift A German scientist named A German scientist named

Alfred Wegener formed Alfred Wegener formed the hypothesis that the the hypothesis that the continents had moved!continents had moved!

He proposed that all the He proposed that all the continents had once been continents had once been joined together in a single joined together in a single landmass and have since landmass and have since drifted apart.drifted apart.

The Theory of Continental DriftThe Theory of Continental Drift Wegener’s idea that Wegener’s idea that

the continents slowly the continents slowly moved over the earth moved over the earth became known as became known as continental drift.continental drift.

Unfortunately Wegener Unfortunately Wegener could not provide a could not provide a satisfactory explanation satisfactory explanation for the force that for the force that pushed or pull the pushed or pull the continents. Therefore continents. Therefore most geologists most geologists rejected his idea.rejected his idea.

Evidence of Continental DriftEvidence of Continental Drift Evidence from Evidence from

landforms:landforms: Mountain ranges and Mountain ranges and

other features on the other features on the continents provided continents provided evidence for continental evidence for continental drift.drift.

Mountain ranges in Mountain ranges in South Africa line up with South Africa line up with mountain ranges in mountain ranges in Argentina (South Argentina (South America).America).

Evidence for Continental DriftEvidence for Continental Drift Evidence from fossilsEvidence from fossils A fossil is any trace of A fossil is any trace of

an ancient organism an ancient organism that has been that has been preserved in rock.preserved in rock.

Glossopteris fossils Glossopteris fossils have been found in have been found in rocks in Africa, South rocks in Africa, South America, Australia, America, Australia, India, and Antarctica.India, and Antarctica.

Evidence for Continental DriftEvidence for Continental Drift Evidence from climateEvidence from climate Fossils of tropical Fossils of tropical

plants have been found plants have been found too far north or south to too far north or south to have survived.have survived.

Glacier deposits are Glacier deposits are found too close to the found too close to the equator.equator.

These clues provide These clues provide evidence that evidence that continental drift really continental drift really happened.happened.

Rejection!!Rejection!!

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

Let’s See What Wegner Thought Let’s See What Wegner Thought Really Happened!Really Happened!

http://www.suu.edu/faculty/colberg/Hazards/PlateTectonics/18_Pangaea.html

http://www.exploratorium.edu/origins/antarctica/ideas/gondwana2.html

Energy is constantly Energy is constantly on the move!on the move!

The movement of The movement of energy from warmer energy from warmer object to a cooler object to a cooler object is called a heat object is called a heat transfertransfer

There are three types There are three types of heat transfer: of heat transfer: radiation, conduction, radiation, conduction, and convection.and convection.

RadiationRadiation Radiation is the Radiation is the

transfer of energy transfer of energy through empty space.through empty space.

Heat transfer by Heat transfer by radiation takes place radiation takes place with no direct contact with no direct contact between a heat between a heat source and an object.source and an object.

ConductionConduction

Heat transfer by direct Heat transfer by direct contact of particles is contact of particles is called conduction.called conduction.

When your hands When your hands touches a metal spoon touches a metal spoon sitting in a boiling pot of sitting in a boiling pot of soup, the heat from the soup, the heat from the bottom of the pot is bottom of the pot is transferred to your transferred to your hand by conduction.hand by conduction.

ConductionConduction

ConvectionConvection Convection is the Convection is the

transfer of heat by transfer of heat by the movement of a the movement of a heated fluid.heated fluid.

Convection deals Convection deals with density.with density.

Density is the Density is the measure of how measure of how much mass is there much mass is there in a certain volume of in a certain volume of a substance.a substance.

ConvectionConvection When a liquid or gas When a liquid or gas

is heated, the is heated, the particles move faster particles move faster and the density and the density decreases.decreases.

As the fluid becomes As the fluid becomes cooler, its density cooler, its density increases.increases.

As density increases, As density increases, the fluid sinks.the fluid sinks.

Heat Rises!!Heat Rises!!

ConvectionConvection

The heating and cooling of The heating and cooling of the fluid, changes in the the fluid, changes in the fluid’s density, and the fluid’s density, and the force of gravity combine to force of gravity combine to set convection currents in set convection currents in motion.motion.

Without heat, convection Without heat, convection currents will eventually currents will eventually come to a stop.come to a stop.

Convection Currents in the MantleConvection Currents in the Mantle

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

Convection in the Earth’s MantleConvection in the Earth’s Mantle

The crust “floats” on the The crust “floats” on the mantle, just like mantle, just like Cheerios float on the Cheerios float on the surface of milk. The surface of milk. The convection currents in convection currents in Earth’s mantle cause the Earth’s mantle cause the crust to move ever so crust to move ever so slightly, therefore, slightly, therefore, allowing continents to allowing continents to drift.drift.

Plate TectonicsPlate Tectonics Based on the knowledge that the lithospheric Based on the knowledge that the lithospheric

plates float on the asthenosphere, the theory plates float on the asthenosphere, the theory of plate tectonics was developed.of plate tectonics was developed.

Radiation, Conduction, and Radiation, Conduction, and ConvectionConvection