Plate Tectonics

What Did The Earth Look Like

In The Past?

CONTINENTAL DRIFT THEORY

• Alfred Wegener - 1912 - developed theory of a large land mass called Pangaea (means all land). The ocean was called Panthalassa. He thought Pangaea broke apart and floated on the ocean floor due to earth’s rotation.

• Evidence of proof: fossils of plants & animals, rocks, glacial clues, matching climate and continents fitting together like a puzzle.

• Theory was ignored because there was no explanation of how, when, or why these changes took place.

Evidence of Continental Drift

MESOSAURUS - M Freshwater/Land reptile

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G

GLOSSOPTERIS - GFossil plant /Similar climate

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MM

G

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CLIMATE - CWarm weather plants

GLACIERS - GLGlacial deposits &Rock surfaces scoured& polished by glaciers

GL

C/W

GL

GL

GL

ROCK CLUE - RRock structures aresimilar types & ages

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LYSTROSAURUS - LA small reptile

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Principle of Uniformitariantism - states that the processes we see changing Earth’s surface today are the same as those that changed it in the past.

Principle of Superposition - states that layers of sedimentary rock near the surface are younger than layers of rock deeper down, unless somethingHas disturbed the layers.

Unconformity - is a place where rock layers are missing.

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PLATE TECTONICS

In 1968, scientists aboard the research ship Glomar Challenger drilled into the seafloor for rock samples. They discovered that the youngest rocks were located on the mid-ocean ridge in the Atlantic Ocean. The rocks became older as they moved farther away from the ridge.

This gave evidence to the theory of seafloor spreading that was suggested by a Princeton University scientist, Harry Hess. Hess was on a Navy vessel in WW II,mapping the ocean floor with a fathometer - a type of sonar that used echo sounding to help ships know where the bottom of the ocean floor was. He proposed that hot, less dense material below the crust rises toward the surface at the mid ocean ridges, flowing sideways, carrying the seafloor away from the ridge in both directions.

Divergent plates spread apart from each other, creating newcrust. Hot, molten magma rises to the surface of the oceanfloor, pushing the floor outward. On the Mid- Atlantic Ridge, the North American plate is movingaway from the Eurasian and the African Plates. This process is making the Atlantic Ocean larger.

The Great Rift Valley in eastern Africa is becoming a divergentplate boundary. Iceland is also.

When new seafloor is created by this plate movement, the magma cools quickly, forming a crust made of basalt rock. This creates a very heavy, dense crust, even though it is only 3 miles thick.

SEAFLOORSPREADING

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Names of Plates

The Earth’s crust appears to be broken into pieces like a puzzle, which are called plates. These rigid plates are being moved by the convection currentsin the hot, molten mantle. The plates spread apart, collide or slide past each other, causing earthquakes, volcanoes, mountains and ridges. The plates can move 2 to 15 centimeters each year.

Plates Move Away From Each OtherThis is called Divergence – these are constructive

boundaries since they produce new land

Africa and ArabiaNorth America

and Eurasia

Mid-Atlantic Ridge

Rift Valley – if the land is above water

Sea Floor Spreading – when the land is below water

Divergence – Moving Apart

Plates Move Toward Each OtherThis is called Convergence – these are destructive

boundaries since they deform the plates

Continent/ContinentOcean/Continent

Ocean/Ocean

Subduction

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13. Convergent

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Subduction15.

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18. Andes Mountains

Convergent19.

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Folded Mountains21.

Convergence – Moving TogetherTrenches

Mountains

Structural Mountains

Volcanic Mountains

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A convergent boundary is created when two plates collide into each other. When this occurs, mountains and/or volcanoes are created and earthquakes can happen. When the heavier oceanic floor collides into the lighter continental crust, the continental crust is pushed over the oceanic crust. The oceanic crust “dives” under the continental crust creating a subduction zone. Land is lostin this area. The Pacific Ocean isgetting smaller because of this process.

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Rock parts pulled

Apart from faults

Sierra &Teton Range

Rock layers folded

Orcompressed

Appalachians

Plates sink andMelting occursLava piles upFrom magma

HawaiianIslands

Forces in EarthPush on crust

Rocky &

Adirondack

Active Movements - Faults

One day – Los Angeles and San Francisco will be next to each other

TRANSFORM FAULT

This type of boundary occurs where two plates slide past one another. They move in opposite directions or in the same direction at different rates. When one plate slips past another suddenly, earthquakes occur.

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24. Shearing

Transform

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Foot Wall Hanging Wall

FAULTS are fractures or break in earth’s crust - movement has taken place - rock strata layers do not match - create mountains- Niagara Falls.

Blocks are pulled apartoverlying block movesdown the fault plane.A spreading zone.Sierra Nevada's

Squeezing or compressing Blocks are pushed togetherMoves up the fault plane.Himalayas Mts. - India

Transform - strike -slip fault - a lateral faultSlide past each other.San Andreas, CA.

Foot Wall Hanging Wall

DIVERGENT

CONVERGENTCONVERGENT

OCEAN

LAND

Earthquakes, Volcanoes & Mountains

Earthquakes

Earthquakes & Volcanoes

Divergent

Convergent

Convergent

Convergent

Transform

Sea floor spreading

Mid ocean ridge

Rift Valley Iceland

Mid-Atlantic Ridge

Collision ofOcean-ocean

Subduction Trench

Island arc ConvergentOcean-ocean

subductionVolcanicmountains

Collision ofContinental/

oceanicTrench

AndesMountains

Shearing

Collision ofContinental/continental

Foldedmountains

HimalayaMountains

Transformfault

San Andreasfault

Types of Boundary – convergent, divergent, transformChoices of Motion at Boundary – collision of continental/continentalCollision of oceanic/oceanicCollision of continental/oceanicOcean floor spreadingShearingSubductionLand Features Formed -Island arcFolded mountainsMid-ocean ridgeRift valleyTransform faultTrenchVolcanic MountainsActual Examples –Andes MountainsAleutian IslandsHimalaya MountainsIcelandMid-Atlantic RidgeSan Andreas