- Alfred Wegener proposed the theory of continental drift, suggesting that continents had once been joined together in a single landmass called Pangaea before drifting apart. However, he could not provide a satisfactory explanation for the force driving the drift. - Evidence from matching landforms, fossil distributions, and climate clues in rock strata provided growing support for continental drift, but it took decades for most geologists to accept the theory. - Convection currents in the Earth's mantle, driven by heat from the core, cause the crust and tectonic plates to slowly move over time, allowing for continental drift. This theory of plate tectonics eventually replaced continental drift as the explanation for drifting continents.

1. Drifting ContinentsDrifting Continents
Did Pangaea Exist?Did Pangaea Exist?

2. The Theory of Continental DriftThe Theory of Continental Drift
 A German scientist namedA German scientist named
Alfred Wegener formedAlfred Wegener formed
the hypothesis that thethe hypothesis that the
continents had moved!continents had moved!
 He proposed that all theHe proposed that all the
continents had once beencontinents had once been
joined together in a singlejoined together in a single
landmass and have sincelandmass and have since
drifted apart.drifted apart.

3. The Theory of Continental DriftThe Theory of Continental Drift
 Wegener’s idea thatWegener’s idea that
the continents slowlythe continents slowly
moved over the earthmoved over the earth
became known asbecame known as
continental drift.continental drift.
 Unfortunately WegenerUnfortunately Wegener
could not provide acould not provide a
satisfactory explanationsatisfactory explanation
for the force thatfor the force that
pushed or pull thepushed or pull the
continents. Thereforecontinents. Therefore
most geologistsmost geologists
rejected his idea.rejected his idea.

4. Evidence of Continental DriftEvidence of Continental Drift
 Evidence fromEvidence from
landforms:landforms:
 Mountain ranges andMountain ranges and
other features on theother features on the
continents providedcontinents provided
evidence forevidence for
continental drift.continental drift.
 Mountain ranges inMountain ranges in
South Africa line upSouth Africa line up
with mountain rangeswith mountain ranges
in Argentina (Southin Argentina (South
America).America).

5. Evidence for Continental DriftEvidence for Continental Drift
 Evidence from fossilsEvidence from fossils
 A fossil is any trace ofA fossil is any trace of
an ancient organisman ancient organism
that has beenthat has been
preserved in rock.preserved in rock.
 Glossopteris fossilsGlossopteris fossils
have been found inhave been found in
rocks in Africa, Southrocks in Africa, South
America, Australia,America, Australia,
India, and Antarctica.India, and Antarctica.

6. Evidence for Continental DriftEvidence for Continental Drift
 Evidence from climateEvidence from climate
 Fossils of tropicalFossils of tropical
plants have beenplants have been
found too far north orfound too far north or
south to have survived.south to have survived.
 Glacier deposits areGlacier deposits are
found too close to thefound too close to the
equator.equator.
 These clues provideThese clues provide
evidence thatevidence that
continental drift reallycontinental drift really
happened.happened.

7. 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.

8. Let’s See What Wegner ThoughtLet’s See What Wegner Thought
Really Happened!Really Happened!
 http://www.suu.edu/faculty/colberg/Hazards/Plhttp://www.suu.edu/faculty/colberg/Hazards/Pl
 http://www.exploratorium.edu/origins/antarcticahttp://www.exploratorium.edu/origins/antarctica

9.  Energy is constantlyEnergy is constantly
on the move!on the move!
 The movement ofThe movement of
energy from warmerenergy from warmer
object to a coolerobject to a cooler
object is called a heatobject is called a heat
transfertransfer
 There are three typesThere are three types
of heat transfer:of heat transfer:
radiation, conduction,radiation, conduction,
and convection.and convection.

10. RadiationRadiation
 Radiation is theRadiation is the
transfer of energytransfer of energy
through empty space.through empty space.
 Heat transfer byHeat transfer by
radiation takes placeradiation takes place
with no direct contactwith no direct contact
between a heatbetween a heat
source and an object.source and an object.

11. ConductionConduction
 Heat transfer by directHeat transfer by direct
contact of particles iscontact of particles is
called conduction.called conduction.
 When your handsWhen your hands
touches a metal spoontouches a metal spoon
sitting in a boiling pot ofsitting in a boiling pot of
soup, the heat from thesoup, the heat from the
bottom of the pot isbottom of the pot is
transferred to yourtransferred to your
hand by conduction.hand by conduction.

12. ConductionConduction

13. ConvectionConvection
 Convection is theConvection is the
transfer of heat bytransfer of heat by
the movement of athe movement of a
heated fluid.heated fluid.
 Convection dealsConvection deals
with density.with density.
 Density is theDensity is the
measure of howmeasure of how
much mass is theremuch mass is there
in a certain volume ofin a certain volume of
a substance.a substance.

14. ConvectionConvection
 When a liquid or gasWhen a liquid or gas
is heated, theis heated, the
particles move fasterparticles move faster
and the densityand the density
decreases.decreases.
 As the fluid becomesAs the fluid becomes
cooler, its densitycooler, its density
increases.increases.
 As density increases,As density increases,
the fluid sinks.the fluid sinks.
 Heat Rises!!Heat Rises!!

15. ConvectionConvection
 The heating and cooling ofThe heating and cooling of
the fluid, changes in thethe fluid, changes in the
fluid’s density, and thefluid’s density, and the
force of gravity combine toforce of gravity combine to
set convection currents inset convection currents in
motion.motion.
 Without heat, convectionWithout heat, convection
currents will eventuallycurrents will eventually
come to a stop.come to a stop.

16. Convection Currents in the MantleConvection Currents in the Mantle
 The heatThe heat
source forsource for
thesethese
convectionconvection
currents in thecurrents in the
mantle comesmantle comes
from the heatfrom the heat
of the Earth’sof the Earth’s
core.core.

17. Convection in the Earth’s MantleConvection in the Earth’s Mantle
 The crust “floats” on theThe crust “floats” on the
mantle, just likemantle, just like
Cheerios float on theCheerios float on the
surface of milk. Thesurface of milk. The
convection currents inconvection currents in
Earth’s mantle cause theEarth’s mantle cause the
crust to move ever socrust to move ever so
slightly, therefore,slightly, therefore,
allowing continents toallowing continents to
drift.drift.

18. Plate TectonicsPlate Tectonics
 Based on the knowledge that the lithosphericBased on the knowledge that the lithospheric
plates float on the asthenosphere, the theoryplates float on the asthenosphere, the theory
of plate tectonics was developed.of plate tectonics was developed.

19. Radiation, Conduction, andRadiation, Conduction, and
ConvectionConvection