Plate TectonicsHi,

I am Zed and I am going to take you on a trip learning about

Plate Tectonics And I am Buddy…Zed’s

mascot

Continental Drift

• Alfred Wegener – proposed that continents were not always where they are now – called it continental drift.

• Evidence:– Fossils– Landforms– Climate

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• Wegener’s hypothesis was rejected because he couldn’t explain how it happened.

• That evidence was found in 1947 when scientists discovered the mid-ocean ridge.

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Mid-ocean Ridges

• Undersea mountain ranges that encircle the globe (like stitches on a baseball).

• New crust is formed at the ridges.

• Sea-floor crust is very young and the crust closest to the ridges is the youngest.

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Sea-floor spreading

• In the 1950’s scientists started to believe that the mid-ocean ridges were pushing the crust apart.

• New crust forms at the ridge and is pushed away from the ridge – the sea-floor is spreading

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• We cannot see it spread.

• Evidence for sea-floor spreading:– Rocks closest to the ridge are younger than

those further away.– Paleomagnetism

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Paleomagnetism• When new crust cools quickly – the magnetic

pieces in them line up and point north.

• Every 70 million years or so, the magnetic poles reverse – north is south and south is north.

• This can be seen inside of rocks

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• The crust on either side of the mid-ocean ridges shows patterns of magnetic reversals.

• These patterns show that the sea-floor is spreading.

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Plate Tectonics part 2

How continents move.

• The continents sit on top of pieces of the lithosphere.

• The lithosphere sits on top of the asthenosphere.

• The asthenosphere is hot and soft and moves slowly, like putty.

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• The chunks of the lithosphere (plates) move around on top of this soft, hot layer.

• Plates can be made of oceanic crust, continental crust, or both.

• Oceanic crust is more dense than continental crust.

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Plate contact

• Anywhere one plate touches another there are usually earthquakes and volcanoes.

• All of the plates are in motion.

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Plate boundaries

• Plate boundaries are the places that plates touch.

• There are 3 types:– Convergent – Where plates push towards

each other.– Divergent – Where plates are moving away

from each other.– Transform – Where they are sliding past each

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Plate Boundaries

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Why do the plates move?

• Convection – When a liquid or a gas is heated it becomes less dense.– The cooler and more dense material sinks.– This pushes aside the hot material and it

rises.– This sets up convection currents.

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• There are convection currents in mantle.

• Heat from the core drives these convection currents.

• These currents drag the plates above them.

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Plate Tectonics Notes

Part 3

Effects of continental change• As continents move their climate can

change.– Ex. Parts of Antarctica used to be covered

with jungle.

• Living organisms change as well.– When a population is separated it can evolve

differently until they are no longer the same species.

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Supercontinent

• A supercontinent is when most of the earth’s landmasses are attached.

• Pangaea was the last supercontinent.

• It broke apart and continents that were once attached are moving apart.

• In about 250 million years a new supercontinent might form.

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Rock Stress

• Rocks can be changed as pressure is added in different ways.

• Compression is when rocks are pushed together.– This can cause rocks to fold or crack.– Happens mostly at convergent boundaries.

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• Tension happens where rocks are being pulled away from each other.– Mainly happens at divergent boundaries.– Rocks can become thinner or crack.

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• Shear stress – when rocks are being pushed in opposite directions (sideways)– Happens mainly at transform boundaries– Causes rocks to twist, bend, or break.

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Mountains

• Mountains are formed mainly by the collision of 2 plates.

• When oceanic crust meets continental crust the continental crust is pushed.

• The oceanic crust sinks underneath and melts forming volcanoes.

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• When two oceanic plates collide, the more dense one sinks below the other.

• As it sinks, it melts to form volcanoes.

• Examples are Japan and Hawaii

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• When two continents collide, the crust is pushed upwards.

• The Himalayas were formed this way when India ran into Asia. (still growing)

• Some crust may also sink and melt forming volcanoes.

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Types of Mountains

• Folded Mountains– Highest mountain ranges in the world– Tectonic plates colliding squeeze rock layers

upward, folding and faulting them– Himalayas, Appalachians, Alps are examples

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Types of Mountains

• Fault-Block Mountains– Crust has been stretched and broken into

large blocks – Happens where plates are being pulled apart– Sierras, Wasatch, and Teton’s are examples

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• Fault Block Mountains•

Provided by:Sandy Gertsch, Utah County, Utah, School System

• Thirty miles south of Salt Lake City, near the mouth of Provo Canyon in Orem, Utah is an excellent example of fault block mountains. The north-south trending Wasatch Range extends throughout the center of Utah. The western flank of the range is very steep and relatively straight, the result of displacement along the extensive and still-active Wasatch Fault. Summits along the crest of the range have elevations between 9,000 and 10,000 feet. The mountain-sized fault blocks of this region developed in a fairly orderly fashion, breaking roughly at right angles to the westward direction of stress. As visible in this photo, the truncated spurs of the Wasatch Mountains provide evidence that movement on the Wasatch fault is geologically recent. Utah lays claim to many thousands of faults, large and small. Mountains have been formed by normal faults, reverse faults, thrust faults and extension or detachment faults. The valley held an arm of Lake Bonneville, a lake that formerly covered this area 25,000 years ago in the Pleistocene era. This lake varied in level over the years and left clearly seen shorelines, benches, ridges and gravel bars. The slope on the left of this picture is an example of this ancient deposition.

Wasatch Mountains in Utah County

Types of Mountains• Domed Mountains

– Rare type formed when magma rises and pushes up against the surface without breaking through

– A rounded mountain with a center peak– Henry Mts. In Utah, Black Hills of S.D. are

examplesHenry Mountains In Utah

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Salt Domed Mountain• Astronaut view of domed mountain created when salt,

underlain with petroleum deposits was squeezed up through more dense rock layers towards the surface.

The End ?????