Unit 4Unit 4Chapter 10Chapter 10

Plate TectonicsPlate Tectonics

Section 1 Continental DriftSection 1 Continental Drift

Wegener’s HypothesisWegener’s Hypothesis  In 1912 German scientist Alfred Wegener In 1912 German scientist Alfred Wegener

proposed the theory of proposed the theory of Continental Continental Drift. Drift. He stated that the continents He stated that the continents seemed to fit together and have since seemed to fit together and have since moved away from each other. moved away from each other. According to Wegener, the super According to Wegener, the super continent started breaking up about continent started breaking up about 200 million years ago.200 million years ago.

EvidenceEvidenceFossil EvidenceFossil EvidenceWegener found similarities in the coastlines of the continents, and he found other Wegener found similarities in the coastlines of the continents, and he found other

evidence as well. He found identical fossils of the mesosaurus that were located evidence as well. He found identical fossils of the mesosaurus that were located on the coasts of Eastern South America and Western Africa. This animal did not on the coasts of Eastern South America and Western Africa. This animal did not swim across the ocean.swim across the ocean.

  Evidence from Rock FormationsEvidence from Rock FormationsAlong with fossil evidence, rock evidence pointed to the lands being joined at one Along with fossil evidence, rock evidence pointed to the lands being joined at one

time. The Appalachian Mountains extend Northward along Eastern Coast of time. The Appalachian Mountains extend Northward along Eastern Coast of North America are the same age and structure of the mountains found in North America are the same age and structure of the mountains found in Greenland, Scotland and Northern Europe.Greenland, Scotland and Northern Europe.

  Climatic EvidenceClimatic EvidenceAncient glacial debris was found in Southern Africa and South America.Ancient glacial debris was found in Southern Africa and South America.  Missing mechanismsMissing mechanismsWegener could not come up with the “how” part of the hypothesis. He died in 1930 Wegener could not come up with the “how” part of the hypothesis. He died in 1930

before anyone would discover the actual answer.before anyone would discover the actual answer.  

Mid Ocean RidgesMid Ocean RidgesIn 1947 Scientists set out to map the Mid-Atlantic Ridge, which was part of the In 1947 Scientists set out to map the Mid-Atlantic Ridge, which was part of the

underground mountain ranges. They discovered two surprising trends.underground mountain ranges. They discovered two surprising trends.

Sediments were thinner near the center and thicker farther away from the center.Sediments were thinner near the center and thicker farther away from the center.The ocean floor was younger than the continents. Youngest rocks were by the mid-The ocean floor was younger than the continents. Youngest rocks were by the mid-

ocean ridge.ocean ridge.

Sea-Floor SpreadingSea-Floor Spreading

In the late 1950’s geologist Harry Hess came up In the late 1950’s geologist Harry Hess came up with a new hypothesis. He proposed that the with a new hypothesis. He proposed that the center valley was actually a ridge where center valley was actually a ridge where molten rock would come to the surface and fill molten rock would come to the surface and fill the cracks and push the land away.the cracks and push the land away.

  Robert Dietz renamed the process as “Sea Floor Robert Dietz renamed the process as “Sea Floor

Spreading”. Hess’s hypothesizes were proven Spreading”. Hess’s hypothesizes were proven with more evidence discovered in the mid with more evidence discovered in the mid 1960’s. The evidence was discovered through 1960’s. The evidence was discovered through paleomagnetism which is the study of the paleomagnetism which is the study of the magnetic properties of rocks.magnetic properties of rocks.

PaleomagnetismPaleomagnetismPaleomagnetism- when magma hardens the iron-rich Paleomagnetism- when magma hardens the iron-rich mineral aligns with Earth’s magnetic field.mineral aligns with Earth’s magnetic field.

Magnetic ReversalsMagnetic ReversalsIt has been discovered that Earth’s magnetic properties have changed orientation. It has been discovered that Earth’s magnetic properties have changed orientation.

Since the rocks magnetism goes along with the magnetic field, Scientists have Since the rocks magnetism goes along with the magnetic field, Scientists have discovered a pattern of normal (points north) and reversal (points south) discovered a pattern of normal (points north) and reversal (points south) magnetic orientations in rocks along the mid ocean ridge. The pattern it magnetic orientations in rocks along the mid ocean ridge. The pattern it created is called the geomagnetic reversal time scale.created is called the geomagnetic reversal time scale.

  Magnetic SymmetryMagnetic SymmetryScientists discovered that our form the center of the mid ocean ridge to the edges Scientists discovered that our form the center of the mid ocean ridge to the edges

of the continents a pattern of normal and reversed polarity formed. These of the continents a pattern of normal and reversed polarity formed. These patterns were mirror images on either side of the ridge. They also discovered patterns were mirror images on either side of the ridge. They also discovered the youngest rocks were on either side of the ridge with the oldest rocks by the the youngest rocks were on either side of the ridge with the oldest rocks by the continents.continents.

The symmetry of both the magnetic patterns and the rock ages supports Hess’s The symmetry of both the magnetic patterns and the rock ages supports Hess’s theory.theory.

Wegener RedeemedWegener RedeemedAnother group of scientists discovered the reversal pattern on land was similar to Another group of scientists discovered the reversal pattern on land was similar to

the one in the ocean. This added to the support of the continental drift theory. the one in the ocean. This added to the support of the continental drift theory. They also suggested that the mechanics involved was similar to a conveyor belt They also suggested that the mechanics involved was similar to a conveyor belt moving on both sides of the mid ocean ridge.moving on both sides of the mid ocean ridge.

Section 2 The Theory of Plate TectonicsSection 2 The Theory of Plate Tectonics

In the 1960s, the evidence supporting the continental drift theory and In the 1960s, the evidence supporting the continental drift theory and sea floor spreading lead to a new theory called Plate Tectonics. sea floor spreading lead to a new theory called Plate Tectonics.

  Plate Tectonics -Plate Tectonics -

Is the study of the formation and movement of those platesIs the study of the formation and movement of those platesThe plates are attached to the lithosphere and move that way.The plates are attached to the lithosphere and move that way.

  How continents MoveHow continents Move  Lithosphere - solid layer of crust & uppermost part of the mantleLithosphere - solid layer of crust & uppermost part of the mantle

-Similar composition (100 kms)-Similar composition (100 kms)

Two types of crustTwo types of crustContinental – made up of rocks rich in silica (granites), less dense 2.7Continental – made up of rocks rich in silica (granites), less dense 2.7Oceanic – made up of rocks rich in iron and magnesium (basalts), Oceanic – made up of rocks rich in iron and magnesium (basalts),

more more dense 3.0dense 3.0

  Asthenosphere -lower part of the lithosphere similar composition but Asthenosphere -lower part of the lithosphere similar composition but

much hotter almost melted - the rock flows in CONVECTION much hotter almost melted - the rock flows in CONVECTION CURRENTS which allows the rigid upper crust to move.CURRENTS which allows the rigid upper crust to move.

Tectonic PlatesTectonic Plates

There are approximately 15 major plates that fit together on There are approximately 15 major plates that fit together on the earth’s surface like a jigsaw puzzle.the earth’s surface like a jigsaw puzzle.

http://www.p12.nysed.gov/osa/reftable/earthscience-rt/esrt201http://www.p12.nysed.gov/osa/reftable/earthscience-rt/esrt2010-engw.pdf0-engw.pdf

  

EarthquakesEarthquakesSudden shifts or movements along plate boundariesSudden shifts or movements along plate boundaries

  

VolcanoesVolcanoesThey are formed when the movement of plates generates a They are formed when the movement of plates generates a

magma buildup that erupts.magma buildup that erupts.

Types of BoundariesTypes of BoundariesBoundaries are areas on Earth’s surface where volcanic and Boundaries are areas on Earth’s surface where volcanic and earthquake activity occurs.earthquake activity occurs.

Diverging Boundaries Diverging Boundaries

When two plates moving apart, deep areas the length of When two plates moving apart, deep areas the length of the ridgethe ridge

Mid ocean ridges (between America & Africa)Mid ocean ridges (between America & Africa)

Convergent Boundaries Convergent Boundaries - 2 plates moving together - 2 plates moving together (converging)(converging)

Convergent Boundaries - Convergent Boundaries - 2 plates moving together (converging)2 plates moving together (converging)

Collision Boundary -two continents colliding together to make a larger continent - Collision Boundary -two continents colliding together to make a larger continent - India moving into Asia- Himalayan Mountains are the result.India moving into Asia- Himalayan Mountains are the result.

  Transform Boundaries -plates sliding past each other - California/Pacific plate Transform Boundaries -plates sliding past each other - California/Pacific plate

sliding past the American Platesliding past the American Plate

  Fault -crack in the earth's crust where movement has occurredFault -crack in the earth's crust where movement has occurredSan Andrea's Fault moves 5cm/yearSan Andrea's Fault moves 5cm/year  Thin Skin Thrusting -pushing of thin rock layers at continental margins over long Thin Skin Thrusting -pushing of thin rock layers at continental margins over long

distance (Appalachian Mountains)distance (Appalachian Mountains)  

Causes of Plate MotionCauses of Plate MotionMantle convection is the driving force of the plates. Convection Mantle convection is the driving force of the plates. Convection is the movement of heated material. is the movement of heated material.

Mantle ConvectionMantle ConvectionThis is the heat transfer through the mantle where less dense, heated This is the heat transfer through the mantle where less dense, heated

material rises. The cooler denser material flows away from the hot material rises. The cooler denser material flows away from the hot material and sinks back into the mantle to replace the rising material.material and sinks back into the mantle to replace the rising material.

Moho – Real name Mohorovicic discontinuityMoho – Real name Mohorovicic discontinuityIt is the boundary between the crust and the mantle where dense rock of It is the boundary between the crust and the mantle where dense rock of

the mantle meets less dense rock of the crust. It is an average of 32 the mantle meets less dense rock of the crust. It is an average of 32 km under the continents, and 8 km under the sea. This is where most km under the continents, and 8 km under the sea. This is where most of the action occurs.of the action occurs.

Ridge PushRidge PushThis happens when the cooling lithosphere slides down the slope This happens when the cooling lithosphere slides down the slope formed by the elevation of the mid-ocean ridge. The force formed by the elevation of the mid-ocean ridge. The force pushed the rest of the plate away.pushed the rest of the plate away.

Slab PullSlab PullThis happens when the leading edge of the subducting plate moves This happens when the leading edge of the subducting plate moves

under the upper plate. It pulls the plate back into the under the upper plate. It pulls the plate back into the asthenosphere.asthenosphere.

    

  Scientists believe that all three mechanisms together create the Scientists believe that all three mechanisms together create the

convecting system that makes the Earth’s tectonic plates move convecting system that makes the Earth’s tectonic plates move constantly.constantly.

Section 3 The Changing ContinentsSection 3 The Changing Continents

The continents did not always look they way they do The continents did not always look they way they do now and through time, they will once again change now and through time, they will once again change shape and positions. Remember, we are Dynamic.shape and positions. Remember, we are Dynamic.

  Reshaping Earth’s CrustReshaping Earth’s Crust  Craton – large areas of rock more than 540 million Craton – large areas of rock more than 540 million

years oldyears oldShields – areas of craton exposed to earth’s elementsShields – areas of craton exposed to earth’s elements  Rifting and Continental BreakupRifting and Continental BreakupRiftingRifting

Is the process by which Earth’s crust breaks apart Is the process by which Earth’s crust breaks apart anywhere, either on a continent or in the ocean. It anywhere, either on a continent or in the ocean. It is the pressure build up that causes the crust to is the pressure build up that causes the crust to break and move.break and move.

Terranes and Continental GrowthTerranes and Continental Growth

TerraneTerraneIt is a piece of lithosphere that has a unique geologic historyIt is a piece of lithosphere that has a unique geologic history

Contains rocks & fossils that differ from the surrounding areaContains rocks & fossils that differ from the surrounding areaHas major faults at the boundariesHas major faults at the boundariesHas magnetic properties that do not match an areaHas magnetic properties that do not match an area  As oceanic crust subducts, a terrane is scraped off and becomes As oceanic crust subducts, a terrane is scraped off and becomes

part of the continental crust (accretion). It can also be part of the continental crust (accretion). It can also be continental crusts colliding. The Himalaya Mountains formed continental crusts colliding. The Himalaya Mountains formed this way 500 million years ago.this way 500 million years ago.

  

Effects of Continental ChangeEffects of Continental Change

When the continent moved, it changed the climate. The When the continent moved, it changed the climate. The nearness of the continent to the equator or the poles brought nearness of the continent to the equator or the poles brought about a different climate. The location by oceans and other about a different climate. The location by oceans and other continents plays an important role too. When continents continents plays an important role too. When continents move, they also change the flow of air round the globe.move, they also change the flow of air round the globe.

  Change in ClimateChange in ClimateGeologic evidence shows ice once covered most of Earth’s Geologic evidence shows ice once covered most of Earth’s

surfaces. Even the Sahara had ice. This occurred about 450 surfaces. Even the Sahara had ice. This occurred about 450 million years ago when all the land was located near the South million years ago when all the land was located near the South Pole.Pole.

    Change in LifeChange in LifeThe separating of the continents caused species to have to The separating of the continents caused species to have to

evolve into different ones. Isolation of species also caused life evolve into different ones. Isolation of species also caused life to adapt to its new environments.to adapt to its new environments.

The Supercontinent CycleThe Supercontinent CycleWhen the continents are arranged as to create a large When the continents are arranged as to create a large

landmass called a Supercontinent. These landmass called a Supercontinent. These supercontinents break apart and can form new and supercontinents break apart and can form new and different ones. This is called the Supercontinent cycle.different ones. This is called the Supercontinent cycle.

  Why Super Continents ForWhy Super Continents FormmSupercontinents form when convergent boundaries Supercontinents form when convergent boundaries

between two continents collide, neither plate between two continents collide, neither plate subducts, the boundaries become inactive and a new subducts, the boundaries become inactive and a new supercontinent is formed. When the pressure builds supercontinent is formed. When the pressure builds up, the continent breaks apart.up, the continent breaks apart.

  Formation of PangaeaFormation of PangaeaPangaea formed 300 million years ago. It also formed Pangaea formed 300 million years ago. It also formed

the Appalachian Mountains and the Ural Mountains of the Appalachian Mountains and the Ural Mountains of Russia. The Tethys Sea cut into Pangaea and the Russia. The Tethys Sea cut into Pangaea and the ocean that surrounded it was later called Panthalassa.ocean that surrounded it was later called Panthalassa.

Break up of PangaeaBreak up of Pangaea200 million years ago during the Mesozoic Era, Pangaea broke up into 2 200 million years ago during the Mesozoic Era, Pangaea broke up into 2

continents, Laurasia and Gondwanaland.continents, Laurasia and Gondwanaland.

  

Laurasia drifted northward and rotated and then split into North America and Laurasia drifted northward and rotated and then split into North America and Eurasia with the North Atlantic Ocean between them. It also shrank the Eurasia with the North Atlantic Ocean between them. It also shrank the Tethys Sea to become the Mediterranean Ocean.Tethys Sea to become the Mediterranean Ocean.

  

Gondwanaland also changed, South America and Africa were formed. Then Gondwanaland also changed, South America and Africa were formed. Then about 150 million years ago a split began to happen between South about 150 million years ago a split began to happen between South America and Africa opening up the South Atlantic Ocean. The other chunk America and Africa opening up the South Atlantic Ocean. The other chunk of Gondwanaland broke to form India, Australia and the Antarctic. India of Gondwanaland broke to form India, Australia and the Antarctic. India started to move northward and at about 50 million years ago, it collided started to move northward and at about 50 million years ago, it collided with Eurasia to form the Himalayan Mountains.with Eurasia to form the Himalayan Mountains.

  The Modern ContinentsThe Modern ContinentsAs the continents continued to shift and collide, As the continents continued to shift and collide,

other features were formed. The Rocky other features were formed. The Rocky Mountains, the Alps and the Andes Mountains Mountains, the Alps and the Andes Mountains were all formed at this time.were all formed at this time.

  Geology of the FutureGeology of the FutureSome Scientists believe in approximately 150 Some Scientists believe in approximately 150

million years, Africa may collide with Eurasia million years, Africa may collide with Eurasia and the Mediterranean will close. New and the Mediterranean will close. New subductive zones will form by the East Coast subductive zones will form by the East Coast of North and South America and they will of North and South America and they will collide with Eurasia. The Atlantic Ocean will collide with Eurasia. The Atlantic Ocean will disappear. Mexico’s Baja Peninsula will disappear. Mexico’s Baja Peninsula will become part of Alaska. In about 250 million become part of Alaska. In about 250 million years from now we will have another years from now we will have another supercontinent.supercontinent.