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Continental Drift Continental Drift and and

Plate TectonicsPlate Tectonics

Continental drift: An idea Continental drift: An idea before its timebefore its time

Alfred Alfred WegenerWegenerFirst proposed his continental drift First proposed his continental drift

hypothesis in hypothesis in 19151915 Published Published The Origin of Continents and The Origin of Continents and OceansOceans

Continental drift hypothesisContinental drift hypothesis

Supercontinent called Supercontinent called Pangaea Pangaea began began breaking apart about 200 million years agobreaking apart about 200 million years ago

Continental DriftContinental DriftContinental Drift provides an explanation Continental Drift provides an explanation for why the same for why the same plant and and animal species are found in different parts of the species are found in different parts of the world.world.

It would have been impossible for many of It would have been impossible for many of these species to have crossed the entire these species to have crossed the entire Atlantic Ocean. Ocean.

Also, similar types of Also, similar types of rock have been have been found on different continents. found on different continents.

Continental Drift EvidenceContinental Drift Evidence

Continental DriftContinental Drift

Continental drift hypothesisContinental drift hypothesis

Continents "Continents "drifteddrifted" to present positions " to present positions

Evidence used in support of continental Evidence used in support of continental drift hypothesis drift hypothesis

Fit of the continents Fit of the continents

FossilFossil evidence evidence

Rock type and structural similarities Rock type and structural similarities

PaleoclimaticPaleoclimatic evidence evidence

The Great Debate – The EvidenceThe Great Debate – The Evidence

PangaeaPangaea

The Great DebateThe Great Debate

Objections to the continental drift Objections to the continental drift hypothesis

Inability to provide a mechanism capable of Inability to provide a mechanism capable of moving continents across the globemoving continents across the globe

Wegner suggested that continents broke Wegner suggested that continents broke

through the through the ocean crust, much like ice crust, much like ice breakers cut through icebreakers cut through ice

Evidence - MesosaurusEvidence - Mesosaurus

The Great DebateThe Great Debate

Continental drift and the scientific methodContinental drift and the scientific method

Wegner’s hypothesis was Wegner’s hypothesis was correct in in principle, but contained incorrect detailsprinciple, but contained incorrect details

For any scientific viewpoint to gain wide For any scientific viewpoint to gain wide

acceptance, supporting acceptance, supporting evidence from all from all realms of science must be foundrealms of science must be found

A few scientists considered Wegner’s ideas A few scientists considered Wegner’s ideas plausible and continued the search and continued the search

PaleomagnetismPaleomagnetism

Magnetized minerals in rocksminerals in rocks Show the direction to Earth’s magnetic Show the direction to Earth’s magnetic polespoles

Provide a means of determining their Provide a means of determining their

latitude of origin of origin

Revolution of Continental DriftRevolution of Continental Drift

During the 1950s and 1960s technological strides During the 1950s and 1960s technological strides

permitted extensive permitted extensive mapping of the ocean floorof the ocean floor

Seafloor spreading hypothesisSeafloor spreading hypothesis was proposed by was proposed by Harry Hess in the early 1960sin the early 1960s

Paleomagnetism (evidence of past (evidence of past magnetism recorded in the rocks) was the magnetism recorded in the rocks) was the most convincing evidence set forth to most convincing evidence set forth to support the concepts of continental drift support the concepts of continental drift and seafloor spreadingand seafloor spreading

Plate MotionPlate Motion

http://www.nature.nps.gov/geology/http://www.nature.nps.gov/geology/usgsnps/animate/PLATES_3.MPGusgsnps/animate/PLATES_3.MPG

Plate TectonicsPlate TectonicsPlate tectonics is the theory that the Earth’s Plate tectonics is the theory that the Earth’s lithosphere is divided into lithosphere is divided into tectonic plates that plates that move around on top of the asthenosphere.move around on top of the asthenosphere.

Earth’s major platesEarth’s major plates

Seven major lithospheric plates major lithospheric plates

Plates are in motion and continually changing in Plates are in motion and continually changing in

shape and shape and size

Largest plate is the Largest plate is the Pacific plate plate

Several plates include an entire continent plus a Several plates include an entire continent plus a

large area of large area of seafloor

Plate TectonicsPlate Tectonics

Earth’s major platesEarth’s major platesPlates move relative to each other at a very Plates move relative to each other at a very

slow but slow but continuous raterate

– Average about Average about 5 centimeters (2 inches) per yearcentimeters (2 inches) per year

– CoolerCooler, denser slabs of oceanic lithosphere , denser slabs of oceanic lithosphere

descend into the mantleinto the mantle

Divergent Plate BoundariesDivergent Plate Boundaries

When 2 tectonic plates When 2 tectonic plates SEPARATE, the , the boundary is known as a divergent boundary is known as a divergent boundaryboundary

The 2 plates are moving away from each The 2 plates are moving away from each other.other.

Most divergent boundaries occur on the Most divergent boundaries occur on the seafloor. If they occur on land, it forms a . If they occur on land, it forms a valley called a valley called a trench..

Divergent Plate BoundariesDivergent Plate Boundaries

Divergent BoundariesDivergent Boundaries

http://www.classzone.com/books/http://www.classzone.com/books/earth_science/terc/content/visualizations/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?es0804/es0804page01.cfm?chapter_no=visualizationchapter_no=visualization

Mid-ocean ridges Mid-ocean ridges are the result of are the result of divergent boundariesdivergent boundaries

Mid-Ocean RidgeMid-Ocean Ridge

Convergent Plate BoundariesConvergent Plate Boundaries

When 2 tectonic plates collide, the When 2 tectonic plates collide, the boundary is known as a boundary is known as a convergent convergent boundary. (2 plates come together)boundary. (2 plates come together)

There are There are 33 different types of convergent different types of convergent plate collisions:plate collisions:– Continental-ContinentalContinental-Continental– Continental-OceanicContinental-Oceanic

– Oceanic- Oceanic- OceanicOceanic

Convergent BoundariesConvergent Boundaries

Convergent BoundariesConvergent Boundaries

When two plates collide, the When two plates collide, the LIGHTERLIGHTER of of the plates determines which one comes the plates determines which one comes out on top (if it does).out on top (if it does).


Oceanic-OceanicOceanic-Oceanic

The plate that is The plate that is MOREMORE dense dives dense dives under the other plate and returns to under the other plate and returns to the mantle.the mantle.

This process is This process is SUBDUCTIONSUBDUCTION..

Oceanic-ContinentalOceanic-Continental

The oceanic plate dives The oceanic plate dives UNDERUNDER the the continental plate (called subduction)continental plate (called subduction)http://www.classzone.com/books/http://www.classzone.com/books/earth_science/terc/content/visualizations/earth_science/terc/content/visualizations/es0902/es0902page01.cfm?es0902/es0902page01.cfm?chapter_no=visualizationchapter_no=visualization

Continental-ContinentalContinental-Continental

Subduction does Subduction does NOTNOT take place. take place.

The plates crash head-on, folding over The plates crash head-on, folding over one another, squeezing the crust into a one another, squeezing the crust into a MOUNTAINMOUNTAIN..


Transform BoundariesTransform Boundaries

When 2 tectonic plates slide past one When 2 tectonic plates slide past one another another horizontallyhorizontally, the boundary is a , the boundary is a transform boundary.transform boundary.

San Andreas Fault in San Andreas Fault in CaliforniaCalifornia

Transform boundaries cause Transform boundaries cause earthquakesearthquakes all over the world.all over the world.

San Andreas Fault in San Andreas Fault in CaliforniaCalifornia

Why do the plates move?Why do the plates move?

Three driving forces for plate motion:Three driving forces for plate motion:1.1. Ridge PushRidge Push: because of ridge push, the : because of ridge push, the

oceanic lithosphere slides downhill under oceanic lithosphere slides downhill under the force of gravity.the force of gravity.

2.2. ConvectionConvection: convection causes the oceanic : convection causes the oceanic lithosphere to move sideways and away lithosphere to move sideways and away from the mid-ocean ridge.from the mid-ocean ridge.

3.3. Slab PullSlab Pull: oceanic lithosphere is dense and : oceanic lithosphere is dense and sinks. It pulls the rest of the tectonic plate sinks. It pulls the rest of the tectonic plate with it in a process called slab pull.with it in a process called slab pull.

Tracking the motion of platesTracking the motion of plates

GPSGPS is used to track and measure the rate is used to track and measure the rate of tectonic plate movement.of tectonic plate movement.

Radio signals are beamed from satellites Radio signals are beamed from satellites to ground GPS units.to ground GPS units.

With this information, scientists can With this information, scientists can estimateestimate the amount a plate movements the amount a plate movements within within one yearone year..