Earth ScienceEarth SciencePhysical GeologyPhysical Geology

Plate TectonicsPlate TectonicsChapter 4Chapter 4Notes 1Notes 1

Continental DriftContinental Drift Alfred WegenerAlfred Wegener (1912) (1912)

German scientistGerman scientist All continents were once in one super All continents were once in one super

continent called continent called PangaeaPangaea During the During the Mesozoic EraMesozoic Era, began to break , began to break

upup Wegener died before he found the Wegener died before he found the

reason for continental driftreason for continental drift

Evidence of Continental Evidence of Continental DriftDrift

Similarities in coastlinesSimilarities in coastlines FossilsFossils of the same plants and animals of the same plants and animals

are found on different continentsare found on different continents Geological evidenceGeological evidence begins on one begins on one

continent and ends on anothercontinent and ends on another Climate patternsClimate patterns

Coal deposits found in cold regionsCoal deposits found in cold regions Evidence of glaciers can be found in Evidence of glaciers can be found in

tropical areastropical areas

Final EvidenceFinal Evidence Seafloor SpreadingSeafloor Spreading

In 1947, scientist In 1947, scientist mapped the Mid-mapped the Mid-Atlantic RidgeAtlantic Ridge

Found rocks Found rocks closest to the ridge closest to the ridge were younger than were younger than the rocks closer to the rocks closer to the continentsthe continents

PaleomagnetismPaleomagnetism Evidence for Seafloor SpreadingEvidence for Seafloor Spreading Found there are bands of rocks on Found there are bands of rocks on

the ocean floor that have alternating the ocean floor that have alternating polarities polarities Normal = minerals pointing northNormal = minerals pointing north Reverse = minerals pointing southReverse = minerals pointing south Earth’s magnetic field has reversed itself Earth’s magnetic field has reversed itself

many times in earth’s historymany times in earth’s history

PaleomagnetismPaleomagnetism

Theory of Plate TectonicsTheory of Plate Tectonics Earth’s Crust:Earth’s Crust:

OceanicOceanic ContinentalContinental Together with the rigid upper mantle Together with the rigid upper mantle

make the make the lithospherelithosphere broken into plates that are carried broken into plates that are carried

like blocks of wood on waterlike blocks of wood on water Float on top of the asthenosphere Float on top of the asthenosphere

(like putty)(like putty)

Lithospheric Plate Lithospheric Plate BoundariesBoundaries

Divergent BoundariesDivergent Boundaries Two plates moving away from each Two plates moving away from each

otherother Molten rock fills in the crack that is Molten rock fills in the crack that is

formedformed Most are found on oceanic boundariesMost are found on oceanic boundaries Ex: Mid-Atlantic RidgeEx: Mid-Atlantic Ridge

Convergent BoundariesConvergent Boundaries Two plates moving toward each otherTwo plates moving toward each other

Convergent BoundariesConvergent Boundaries Oceanic and continental crustOceanic and continental crust

Oceanic crust is denser and Oceanic crust is denser and subducted (forced under the other)subducted (forced under the other)

Creates a subduction zone, where the Creates a subduction zone, where the oceanic crust is pushed under the oceanic crust is pushed under the continental crustcontinental crust

Also creates a deep ocean trenchAlso creates a deep ocean trench Water seeps into the mantle and Water seeps into the mantle and

melts the mantle; creates magma and melts the mantle; creates magma and volcanic eruptionsvolcanic eruptions

Convergent BoundariesConvergent Boundaries Continental and continental crustContinental and continental crust

Both are pushed upwardBoth are pushed upward Produces large mountains like the Produces large mountains like the

HimalayasHimalayas Oceanic and oceanic crustOceanic and oceanic crust

One plate is subducted, creates a deep One plate is subducted, creates a deep ocean trenchocean trench

Magma is made and a volcanic island is Magma is made and a volcanic island is createdcreated

Called an island arcCalled an island arc

Transform BoundaryTransform Boundary Two plates grind past one another Two plates grind past one another

horizontallyhorizontally Sudden spurts of movementSudden spurts of movement

Ex: San Andreas Fault in CaliforniaEx: San Andreas Fault in California

Causes of Plate MotionCauses of Plate Motion ConvectionConvection: transfer of heat through : transfer of heat through

movement of heated materialmovement of heated material Hot material rises; Cold material sinksHot material rises; Cold material sinks Creates a convection currentCreates a convection current

Believe there are convection currents in the Believe there are convection currents in the asthenosphereasthenosphere

As the plates move apart, upwellings from As the plates move apart, upwellings from deep in the mantle replace the hard deep in the mantle replace the hard lithospherelithosphere

As the lithosphere becomes older, colder As the lithosphere becomes older, colder and denser, it begins to sink back into the and denser, it begins to sink back into the mantlemantle

HomeworkHomework

Study for Quiz on Ch. 4Study for Quiz on Ch. 4Do Key TermsDo Key Terms