by Alexandra H., Brooke T., help from Tom L., Tim D., and Mr. Brown

Edited by Mr. Ledoux

Theory of Plate TectonicsTheory of Plate Tectonics

Earth’s crust is composed of large plates

These plates float on the mantle below

These plates have always moved (slowly)

This movement shapes our Earth’s surface

What it ExplainsWhat it ExplainsThe theory explains the how and why of…

Mountains

Volcanoes

Earthquakes

Similar prehistoric animals lived at the same time on now widely separated continents

History of Plate TectonicsHistory of Plate Tectonics Continental drift was originally proposed by

Alfred Wegener, a German meteorologist, in 1912

His idea was supported by:The fit of the continentsThe distribution of fossilsSimilar rock sequencesAncient climatesThe apparent wandering of the Earth's polar regions

PangaeaPangaea

Wegener used his observations to hypothesize that all of the present-day continents were once part of a single supercontinent called Pangaea.

SpeciesSpecies Fossils of the same species

were found on several different continents.

Wegener proposed that the species dispersed when the continents were connected and later carried to their present positions as the continents drifted apart.

Rock SequencesRock Sequences Rock sequences in

South America, Africa, India, Antarctica, and Australia are very similar.

Same three layers, same order, in areas now separated by great distances

Why?

Correct! He proposed that

the rock layers were made when all the continents were part of Pangaea.

Drifting Magnetic PolesDrifting Magnetic Poles

Wegener did not Wegener did not believe it possible that believe it possible that the magnetic poles the magnetic poles could move far from could move far from the Earth’s poles.the Earth’s poles.

So the apparent drift So the apparent drift over time could be over time could be explained by the explained by the continents moving. continents moving.

Problems with Wegener’s Problems with Wegener’s TheoryTheory

Wegener’s Theory was not accepted by most geologists.

They said that ocean They said that ocean currents or winds currents or winds could scatter the could scatter the ancient plants and ancient plants and animals.animals.

They also thought that They also thought that maybe it was possible maybe it was possible for the poles to for the poles to wander.wander.

The Big ProblemThe Big Problem

Wegener could not explain how the continents could move.

He couldn’t explain what forces could actually cause the continents to move.

The Big SolutionThe Big Solution Arthur Holmes, (Scottish geologist) made this proposal in 1928.

He believed heat trapped in the Earth caused convection currents, areas where fluids beneath the Earth's crust rise, flow laterally, and then fall. The currents would rise beneath continents, spread laterally, then plunge beneath the oceans.

Unfortunately, Wegener died in 1930

Theory of Plate TectonicsTheory of Plate Tectonics

Totally revolutionized our understanding of the Earth, past and present.

Theory ranks with the theories on evolution, relativity, the Big Bang, and Newton’s Laws.

The Ocean FloorThe Ocean Floor

Landforms on the ocean floor are as Landforms on the ocean floor are as diverse as those on landdiverse as those on land

These landforms are also formed by These landforms are also formed by moving platesmoving plates

Ocean Floor Cont.Ocean Floor Cont.The ocean floor, just like land, has The ocean floor, just like land, has mountains, volcanoes, fault lines, ridges, mountains, volcanoes, fault lines, ridges, valleys, and many other landforms.valleys, and many other landforms.

The Break Up of PangaeaThe Break Up of Pangaea

Pangaea was

the large landmass

that separated to

form the continents

millions of years

ago

Scientific Basic FactsScientific Basic FactsCONTINENTAL CRUSTCONTINENTAL CRUST

Less DenseLess Dense (lighter weight): average density = 2.7 gm per cubic (lighter weight): average density = 2.7 gm per cubic centimeter centimeter Thicker: 0 to 40 km, average 35 km under high mountains, the crust Thicker: 0 to 40 km, average 35 km under high mountains, the crust can be thickened, up to 65 km. Under the craton, the can be thickened, up to 65 km. Under the craton, the average thickness is 30 km. . Mineral Composition: granitic (felsic) rocks such as granodiorite and Mineral Composition: granitic (felsic) rocks such as granodiorite and granite enriched in Potassium (K), Sodium (Na), Aluminum (Al), and granite enriched in Potassium (K), Sodium (Na), Aluminum (Al), and Silica (Si) Silica (Si) "Floats" on top of the Mantle"Floats" on top of the Mantle

Oceanic CrustOceanic Crust OCEANIC CRUSTOCEANIC CRUST More denseMore dense (heavier): average density = 3.0 gm per cubic (heavier): average density = 3.0 gm per cubic

centimeter centimeter Thinner: 0 to 10 km, Thinner: 0 to 10 km, average 5 km, thinnest at Mid-Ocean Ridges Mineral Composition: mafic rocks such as basalt and gabbro Mineral Composition: mafic rocks such as basalt and gabbro

enriched in Magnesium (Mg) and Iron (Fe) enriched in Magnesium (Mg) and Iron (Fe) Underlies Ocean BasinsUnderlies Ocean Basins Also “floats” on the mantleAlso “floats” on the mantle

Convection Currents Inside the Convection Currents Inside the EarthEarth

The tectonic plates float on the magma that lies in the core of the earth

This magma is just one big convection current

Earth’s PlatesEarth’s Plates

About Earth’s PlatesAbout Earth’s PlatesThe different plates were formed when Pangaea broke up.

In all there are 14 (depending on your source)

Continental DriftContinental Drift

Continental Drift ContinuedContinental Drift Continued

Continental drift means that the plates move across the magma.

It happens very slowly…2 inches a year is considered very fast!

4 types of plate boundaries:4 types of plate boundaries:

1. Divergent boundary -- new crust is created as -- new crust is created as the plates pull away from each otherthe plates pull away from each other

2. Convergent boundary -- crust is destroyed as -- crust is destroyed as one plate dives under anotherone plate dives under another

3. Transform boundary -- crust is neither -- crust is neither produced nor destroyed as the plates slide produced nor destroyed as the plates slide horizontally past each otherhorizontally past each other

4. Plate boundary zones -- broad belts in which -- broad belts in which boundaries are not well defined and the effects boundaries are not well defined and the effects of plate interaction are unclearof plate interaction are unclear

Transform BoundaryTransform Boundary

Two plates slip past each other, moving in opposite directions

Edges of crust is not damaged.

Earthquakes often occur

Example: San Andreas fault in California

Divergent BoundariesDivergent Boundaries Plates are moving

away from each other Magma from below is

pushing the plates apart. This creates new crust.

Creates mid-ocean ridges and rift valleys

The rift valley in east Africa is about 3,000 km long.

RiftingRifting

Convergent BoundariesConvergent Boundaries Two plates crash

together More dense plate

slides under the less dense plate.

Old crust is recycled back into the mantle.

Creates: A trench (at least 1

oceanic plate) Mountain ranges (2

continental plates)

SubductionSubduction

Oceanic SubductionOceanic Subduction

Continental SubductionContinental Subduction

Mountain BuildingMountain Building

Convergent boundaries can also cause mountains to be built up by the crust folding.

Himalayan Mountains are formed by India pushing up into Asia

BordersBorders This is where all the action is:This is where all the action is: VolcanoesVolcanoes EarthquakesEarthquakes

Plate BoundariesPlate Boundaries

Hot SpotsHot Spots Plates move over an

area where magma is close to the surface.

Volcanoes occur at the same place, but because the plate is moving, a chain of volcanoes can occur.

Hawaiian Islands were formed this way.

Earth’s CrustEarth’s Crust

Future EarthFuture Earth

What do you think the world will look like in What do you think the world will look like in a million years???a million years???

It is predicted that the continents will It is predicted that the continents will eventually crash together on the other side eventually crash together on the other side of the world, creating a new Pangaea.of the world, creating a new Pangaea.

Future WorldFuture World

BibliographyBibliography

http://www.enchantedlearning.com/subjecthttp://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shts/astronomy/planets/earth/Continents.shtmlml

http://www.platetectonics.com/http://www.platetectonics.com/ http://observe.arc.nasa.gov/nasa/earth/http://observe.arc.nasa.gov/nasa/earth/

tectonics/GRAPHICS/plate_opening.jpgtectonics/GRAPHICS/plate_opening.jpg