Tectonic Plate TheoryTectonic Plate Theory

Understanding Basic Principles of Understanding Basic Principles of Earth Science Related to GeologyEarth Science Related to Geology

Earth’s CrustEarth’s Crust Earth’s crust is the outermost layer.Earth’s crust is the outermost layer. The rigid crust “floats” on the molten part of The rigid crust “floats” on the molten part of

the mantle called the asthenosphere.the mantle called the asthenosphere.

PangeaPangea Pangea was the supercontinent from which all Pangea was the supercontinent from which all

continents have split.continents have split. In 1915 Wegener proposed Earth’s continents looked In 1915 Wegener proposed Earth’s continents looked

this way about 225 million years ago.this way about 225 million years ago. The theory of continental drift was used to explain the The theory of continental drift was used to explain the

current positions of the continents.current positions of the continents. Wegener could not come up with a mechanism for Wegener could not come up with a mechanism for

continental drift.continental drift.

Evidence that Pangea Evidence that Pangea ExistedExisted

Fit of the continentsFit of the continents Fossil similaritiesFossil similarities Rock similaritiesRock similarities Mountain chainsMountain chains **PaleoPaleoclimatic evidence climatic evidence **PaleoPaleomagnetismmagnetism Theory of Plate Tectonics Theory of Plate Tectonics

Fit of the ContinentsFit of the Continents

North and South America match almost North and South America match almost perfectly with Africa and Europeperfectly with Africa and Europe

Fossil SimilaritiesFossil Similarities

**MesoMesosaurussaurus, a reptile similar to an alligator , a reptile similar to an alligator once lived in the shallow waters of both once lived in the shallow waters of both South America and Africa.South America and Africa.

Rock SimilaritiesRock Similarities

Rocks of same age are found in locations of Rocks of same age are found in locations of South America and Africa that were once South America and Africa that were once joined in Pangea.joined in Pangea.

Termination of Mountain Termination of Mountain ChainsChains

The map shows location of Pangean The map shows location of Pangean mountain chains (dark blue) that correspond mountain chains (dark blue) that correspond with current mountain chains.with current mountain chains.

Paleoclimatic EvidencePaleoclimatic Evidence

Glacial deposits at the equatorGlacial deposits at the equator Coral reefs in AntarcticaCoral reefs in Antarctica Therefore the landmasses must have been in different Therefore the landmasses must have been in different

locations in the past.locations in the past.

MagnetismMagnetism

Earth is a bar magnetEarth is a bar magnet Magnetic north and south polesMagnetic north and south poles These are not the same location These are not the same location

as the geographic north and south as the geographic north and south polespoles

Exact location varies year-to-yearExact location varies year-to-year

PaleomagnetismPaleomagnetism

This is magnetism This is magnetism “frozen” in the rock at “frozen” in the rock at the time it was the time it was formed.formed.

Geologists can Geologists can determine pole determine pole reversals by studying reversals by studying rock all over the rock all over the globe.globe.

Sea Floor SpreadingSea Floor Spreading

Surveys of the ocean basins showed a Surveys of the ocean basins showed a system of ridges and trenches.system of ridges and trenches.

This led geologists to come up with the This led geologists to come up with the idea of Sea Floor Spreading.idea of Sea Floor Spreading.

Symmetrical magnetic “stripes” were Symmetrical magnetic “stripes” were discovered on either side of the Atlantic discovered on either side of the Atlantic Mid-ocean ridge.Mid-ocean ridge.

Sea Floor SpreadingSea Floor Spreading

Magnetic Reversals along Magnetic Reversals along a Mid-Ocean Ridge a Mid-Ocean Ridge (“stripes”)(“stripes”)

Oldest rock is farthest from ridge.

Youngest, newest rock is along the ridge.

Theory of Plate TectonicsTheory of Plate Tectonics

A rigid piece of A rigid piece of litholithospheresphere (outer (outer crust) is floating on a partially crust) is floating on a partially plastic (molten, soft) plastic (molten, soft) asthenosphere asthenosphere

Seven Major PlatesSeven Major Plates 3 types of Plate Boundaries3 types of Plate Boundaries

Plate BoundariesPlate Boundaries

**Divergent-Divergent-Spreading Center- Ocean Spreading Center- Ocean ridges and seafloor spreading (Atlantic ridges and seafloor spreading (Atlantic Ocean)Ocean)

**ConvergentConvergent-Creates trenches and -Creates trenches and island arcs (Pacific Ocean)island arcs (Pacific Ocean)

**TransformTransform-Plates move past one -Plates move past one another (San Andreas Fault in another (San Andreas Fault in California)California)

Divergent BoundariesDivergent Boundaries

Magma from deep within Earth forces Magma from deep within Earth forces its way between two plates, pushing its way between two plates, pushing them apart. them apart.

The magma cools and forms new The magma cools and forms new seafloor.seafloor.

More magma emerges and pushes More magma emerges and pushes apart the cooled rock.apart the cooled rock.

Seafloor Spreading/mid-oceanic ridgesSeafloor Spreading/mid-oceanic ridges

Rift ValleyRift Valley

A rift valley forms when a A rift valley forms when a continent is slowing splitting continent is slowing splitting apart along a divergent boundary. apart along a divergent boundary.

The African Rift Valley is an The African Rift Valley is an example.example.

Locations of Seafloor Locations of Seafloor SpreadingSpreading

ConvergentConvergent Plates move togetherPlates move together Oceanic crust slides under continental crust.Oceanic crust slides under continental crust. SubductingSubducting crust slides under. crust slides under. Andes Mountains Chain in South America is an example.Andes Mountains Chain in South America is an example. Mountains formed from volcanoes along the convergent boundaryMountains formed from volcanoes along the convergent boundary ..

Convergent BoundariesConvergent Boundaries

The Pacific Ocean by several The Pacific Ocean by several continental plates.continental plates.

The ocean basin is sliding under the The ocean basin is sliding under the continental plates along the plate continental plates along the plate boundaries.boundaries.

As a result, the Pacific Ocean is As a result, the Pacific Ocean is growing smaller.growing smaller.

Why the Pacific is Shrinking Why the Pacific is Shrinking and the Atlantic is Growingand the Atlantic is Growing

Hawaiian Islands are an Hawaiian Islands are an island arc.island arc.

More Examples of More Examples of Convergent BoundariesConvergent Boundaries

Japanese Islands (Pacific Ocean)Japanese Islands (Pacific Ocean) Cascade Mountains (Northwestern Cascade Mountains (Northwestern

U.S.A.)U.S.A.) Himalaya Mountains (Nepal-AsiaHimalaya Mountains (Nepal-Asia))

Transform Plate Transform Plate Boundary Boundary Plates move past one another along Plates move past one another along

strike-slip faultsstrike-slip faults

What Drives the Tectonic What Drives the Tectonic Plates??Plates??

Convection CellsConvection Cells Hot SpotsHot Spots