Continental DriftContinental Drift

Chapter 10Chapter 10

Wegener’s HypothesisWegener’s Hypothesis

Once a single supercontinentOnce a single supercontinent Started breaking up about 200 myaStarted breaking up about 200 mya Continents drifted to current locationContinents drifted to current location Evidence, but no mechanismEvidence, but no mechanism

PangaeaPangaea

PangaeaPangaea

Wegener’s EvidenceWegener’s Evidence

1.1. FossilsFossils– Similar ones found in areas thought to have been Similar ones found in areas thought to have been

connectedconnected

2.2. Rock formationsRock formations– Rock ages same on African & S. American coastRock ages same on African & S. American coast– Continuation of mountain ranges across continentsContinuation of mountain ranges across continents

3.3. Climatic evidenceClimatic evidence– Glaciers in Africa and S. AmericaGlaciers in Africa and S. America– Tropical fossils in colder climatesTropical fossils in colder climates

Rock EvidenceRock Evidence

Fossil EvidenceFossil Evidence

Climate evidenceClimate evidence

Glacial evidence in south Africa, Australia, South America, and India. Occurred at same time.

Pangaea BreakupPangaea Breakup

Breakup of Pangaea (cont)Breakup of Pangaea (cont)

Breakup of Pangaea (cont)Breakup of Pangaea (cont)

Breakup of Pangaea (cont)Breakup of Pangaea (cont)

Mid – Ocean RidgesMid – Ocean Ridges

Under sea mountain rangesUnder sea mountain ranges Sediment thicker farther away from ridgesSediment thicker farther away from ridges Sediment closer to ridges is youngerSediment closer to ridges is younger Ocean floor is young compared to EarthOcean floor is young compared to Earth

Mid - ocean RidgesMid - ocean Ridges

Mid – Ocean RidgesMid – Ocean Ridges

Sea Floor SpreadingSea Floor Spreading

Suggested by Harry HessSuggested by Harry Hess Ocean ridge is a crack (Rift) in Earth’s crustOcean ridge is a crack (Rift) in Earth’s crust Magma fills the crackMagma fills the crack As ocean floor spreads, continents also As ocean floor spreads, continents also

movemove

Sea Floor SpreadingSea Floor Spreading

Sea Floor SpreadingSea Floor Spreading

PaleomagnetismPaleomagnetism

Study of magnetic properties of rocksStudy of magnetic properties of rocks Iron rich minerals in magma align with Iron rich minerals in magma align with

Earth’s magnetic fieldEarth’s magnetic field As magma solidifies, magnetic orientation As magma solidifies, magnetic orientation

becomes permanentbecomes permanent Residual magnetism is paleomagnetismResidual magnetism is paleomagnetism

Earth as a MagnetEarth as a Magnet

Polar WanderingPolar Wandering

Makes more sense for the continents to move than for the North Pole to move

Magnetic Properties from PangaeaMagnetic Properties from Pangaea

Paths coincide if continents started as Pangaea

Magnetic ReversalsMagnetic Reversals

Earth’s magnetic field does not always point Earth’s magnetic field does not always point northnorth

Magnetic reversals – orientation is opposite Magnetic reversals – orientation is opposite of normalof normal

““Normal” rocks and “Reversal” rocks line up Normal” rocks and “Reversal” rocks line up by time periodby time period

Alternating normal and reversed polarity Alternating normal and reversed polarity over timeover time

Geomagnetic time scaleGeomagnetic time scale

Magnetic ReversalsMagnetic Reversals

Magnetic ReversalsMagnetic Reversals

Plate TectonicsPlate Tectonics

Theory that explains how large pieces of Theory that explains how large pieces of lithosphere, called plates, move and change lithosphere, called plates, move and change shapeshape

Study of formation of features in Earth’s Study of formation of features in Earth’s crustcrust

LithosphereLithosphere

Solid outer layer of EarthSolid outer layer of Earth Consists of the crust and rigid upper part of Consists of the crust and rigid upper part of

the mantlethe mantle Broken into blocks called platesBroken into blocks called plates Plates float on the asthenospherePlates float on the asthenosphere

AsthenosphereAsthenosphere

Solid plastic layer of mantle below the Solid plastic layer of mantle below the lithospherelithosphere

Made of mantle rock that flows very slowlyMade of mantle rock that flows very slowly Allows tectonic plates to moveAllows tectonic plates to move

Lithosphere & AsthenosphereLithosphere & Asthenosphere

Crust typesCrust types

1.1.Oceanic crustOceanic crust– DenseDense– Rich in magnesium and ironRich in magnesium and iron

2.2.Continental crustContinental crust– Low densityLow density

– Rich in silica (SiORich in silica (SiO22))

Continental & Oceanic CrustContinental & Oceanic Crust

Tectonic platesTectonic plates

Can be either or both oceanic and Can be either or both oceanic and continental crustscontinental crusts

15 major plates15 major plates Earthquakes – sudden shifts along plate Earthquakes – sudden shifts along plate

boundariesboundaries Volcanoes – plate motions generate magma Volcanoes – plate motions generate magma

that eruptsthat erupts

Tectonic PlatesTectonic Plates

Types of Plate BoundariesTypes of Plate Boundaries

1.1. Divergent boundariesDivergent boundaries– Plates move away from each otherPlates move away from each other– Most on the ocean floorMost on the ocean floor– Form ocean ridges (rifts)Form ocean ridges (rifts)– Plates separate at rift valleyPlates separate at rift valley

Divergent BoundaryDivergent Boundary

Divergent Boundary (on land)Divergent Boundary (on land)

Types of Plate BoundariesTypes of Plate Boundaries

2.2. Convergent boundariesConvergent boundaries– Plates move toward each otherPlates move toward each other– Plates eventually collidePlates eventually collide– 3 types of collisions3 types of collisions

Convergent BoundaryConvergent Boundary

Continental – Oceanic Crust CollisionsContinental – Oceanic Crust Collisions– Subduction zone – oceanic sinks under Subduction zone – oceanic sinks under

continentalcontinental– Magma rises to surface and forms volcanic Magma rises to surface and forms volcanic

mountainsmountains

Continental – Oceanic Continental – Oceanic CollisionCollision

Convergent BoundaryConvergent Boundary

Oceanic – Oceanic Crust CollisionOceanic – Oceanic Crust Collision– Forms ocean trench (subduction)Forms ocean trench (subduction)– Magma forms island arc (Example: Japan)Magma forms island arc (Example: Japan)

Convergent BoundaryConvergent Boundary

Continental – Continental CollisionContinental – Continental Collision– Forms mountainsForms mountains– Edges crumple and thickenEdges crumple and thicken– Creates upliftCreates uplift

Continent CollisionsContinent Collisions

The HimalayasThe Himalayas

Types of BoundariesTypes of Boundaries

3.3. Transform boundariesTransform boundaries– Plates slide past each otherPlates slide past each other– Sudden motion produces EarthquakesSudden motion produces Earthquakes– No magma involvedNo magma involved

Transform boundaryTransform boundary

San Andreas San Andreas FaultFault

Earthquakes – 1 YearEarthquakes – 1 Year

North America – EarthquakesNorth America – Earthquakes10 Year Period10 Year Period

Causes of Plate MotionCauses of Plate Motion

1.1. Mantle convectionMantle convection– Convection currents drag platesConvection currents drag plates

2.2. Ridge PushRidge Push– Newly formed rock slides downhill at mid Newly formed rock slides downhill at mid

ocean ridgeocean ridge

3.3. Slab pullSlab pull– Subducting plate pulls more crust with itSubducting plate pulls more crust with it

Plate MotionPlate Motion

RiftingRifting Breaking apart of Earth’s crustBreaking apart of Earth’s crust

TerraneTerrane

Piece of Piece of lithosphere lithosphere with a unique with a unique geologic geologic history history incorporated incorporated into another into another piece of piece of lithospherelithosphere

Western U.S. TerraneWestern U.S. Terrane

Alaska AccretionsAlaska Accretions

Continental GrowthContinental Growth

Effects of Continental ChangeEffects of Continental Change

Climate changesClimate changes LifeLife

– As populations As populations separate, new species separate, new species developdevelop