by alexandra h., brooke t., help from tom l., tim d., and mr. brown edited by mr. ledoux
Post on 11-Jan-2016
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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
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