Drifting ContinentsDrifting ContinentsDid Pangea Exist?Did Pangea 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.

Wegener named this Wegener named this supercontinent supercontinent PangeaPangea..

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 driftcontinental 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 landformslandforms::

Mountain ranges and Mountain ranges and other features on the other features on the continents provided continents provided evidence for evidence for continental drift.continental drift.

Mountain ranges in Mountain ranges in South Africa line up South Africa line up with mountain ranges with mountain ranges in Argentina.in Argentina.

Evidence for Continental DriftEvidence for Continental Drift

Evidence from Evidence from fossilsfossils

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 Evidence from

climateclimate Fossils of tropical Fossils of tropical

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

Glacier deposits are Glacier deposits are found too far north to found too far north to have existed.have existed.

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.

Convection Currents in the MantleConvection Currents in the Mantle

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 you hand transferred to you hand by conduction.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 volume of a in a volume of a substance.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 in the Earth’s MantleConvection in the Earth’s 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.

Radiation, Conduction, and Radiation, Conduction, and ConvectionConvection