Plate TectonicsPlate Tectonics

Earth Science Ch. 17Earth Science Ch. 17

Plate tectonicsPlate tectonics

Earth’s crust is “broken” into many platesEarth’s crust is “broken” into many plates

There are 7 large platesThere are 7 large plates

Plates move 1-10 cm per yearPlates move 1-10 cm per year

HowStuffWorksHowStuffWorks Videos "Continental Drift" Videos "Continental Drift"

PlatesPlates

Possible evidence forPossible evidence for moving plates moving plates

Shape of continents (“fit” together)Shape of continents (“fit” together)

Rock formations-p. 444Rock formations-p. 444

Fossil evidence: Fig. 17-2Fossil evidence: Fig. 17-2– Similar fossils found on opposite sides of Similar fossils found on opposite sides of

oceansoceans Ancient climate evidence (coal on Ancient climate evidence (coal on

antarctica, glacial deposits in africa)antarctica, glacial deposits in africa)

Alfred WegenerAlfred Wegener

German scientist who proposed German scientist who proposed “continental drift.”“continental drift.”

Named his supercontinentNamed his supercontinent PangaeaPangaea

Pangaea Fig. 17-1Pangaea Fig. 17-1

How do the continents drift?How do the continents drift?

http://videos.howstuffworks.com/hswhttp://videos.howstuffworks.com/hsw/21687-plate-tectonics-volcanoes-and/21687-plate-tectonics-volcanoes-and-earthquakes-video.htm-earthquakes-video.htm

Sea-floor spreadingSea-floor spreading

Sonar Fig. 17-5Sonar Fig. 17-5

Uses echo-sounding to measure Uses echo-sounding to measure depth of ocean floordepth of ocean floor– Discovered underwater mtn chainsDiscovered underwater mtn chains– And trenchesAnd trenches

MagnetometerMagnetometer: detects changes in : detects changes in magnetic fieldsmagnetic fields

Ocean floorOcean floor

Age of ocean sedimentsAge of ocean sediments

Youngest rocks-Youngest rocks-closer to ridgescloser to ridges

New crust forms at New crust forms at ridgesridges

Oldest are farther Oldest are farther awayaway

Crust is destroyed Crust is destroyed at trenchesat trenches

Plate tectonics Fig. 17-13Plate tectonics Fig. 17-13

Plate boundariesPlate boundaries

Divergent: move apartDivergent: move apart

Convergent: push togetherConvergent: push together

Transform: slide past each otherTransform: slide past each other

Divergent (move apart)Divergent (move apart) Fig. 17-14 Fig. 17-14

Most found on seafloor, but also the Most found on seafloor, but also the East African Rift ValleyEast African Rift Valley

Formation of new crustFormation of new crust

Atlantic Ocean grows about 1” a yearAtlantic Ocean grows about 1” a year

Convergent (come together)Convergent (come together)Fig. 17-15a,b,cFig. 17-15a,b,c

3 types-depends on crust types3 types-depends on crust types

Ocean-oceanOcean-ocean Ocean-continentalOcean-continental Continental-continentalContinental-continental

Ocean-ocean Fig. 17-15aOcean-ocean Fig. 17-15a

One ocean plate One ocean plate subductssubducts, or goes , or goes underneath the other ocean plateunderneath the other ocean plate

A trench formsA trench forms

Crust is destroyed hereCrust is destroyed here

Continent-ocean Fig. 17-15bContinent-ocean Fig. 17-15b-more dense ocean plate sinks-more dense ocean plate sinks

Continental-continentalContinental-continentalFig. 17-15cFig. 17-15c

Both plates are too buoyant to sinkBoth plates are too buoyant to sink

Forms a mtn range insteadForms a mtn range instead

Ex. Himalayas Ex. Himalayas

Transform (slide past) Transform (slide past) Fig. 17-17Fig. 17-17

Crust is fractured, generally forms Crust is fractured, generally forms faultsfaults

Most occur in oceansMost occur in oceans

Most famous example is San Andreas Most famous example is San Andreas Fault in CAFault in CA

San Francisco eartSan Francisco earthquake 1989 - Goohquake 1989 - Google Videogle Video

Possible causes of plate motionsPossible causes of plate motions

Mantle convectionMantle convection

Push and pull of the plates (gravity)Push and pull of the plates (gravity)

The End!The End!

ReferencesReferences