PLATE TECTONICS

Why the Earth is Like It Is

Plate tectonics is the theory that Earth's outer layer is made up of plates, which have moved throughout Earth's history. The theory explains the how and why behind mountains, volcanoes, and earthquakes.

Continental DriftContinental Drift: Alfred Wegener's theory that all continents were once connected in a single, large landmass (called Pangaea) that broke apart about 200 million years ago and drifted slowly to their current positions.

What Did The Earth Look Like In The Past?

What evidence do we have that the continents have moved?Fossil Clues:

Fossils of similar plants and animals have been found on continents that are now very far apart, but were perhaps once joined together.

Climate clues:Evidence of glaciers can be found on land that is now tropical, because that land was once located in a colder region of our planet.

Rock Clues:Similar rock structures can be found on continents that are now far apart, again suggesting that they could have once been joined. Rocks found in the eastern US are similar to those found in western Europe.

Major Tectonic Plates:Tectonic Plates World Map (link)

Do land features continue to change? Are the continents still moving?

The earth’s tectonic plates continue to gradually move even today. The plates interact. Where one plate meets another, is called a boundary.

How do we know?Hot Spots (Hawaii, Yellowstone)

Volcanoes and EarthquakesRing of Fire – very active

region of subduction

Why Do Plates Move?Plates are “pushed” and “pulled” over the surface of the Earth due to unbalanced forces.

When convection currents reach the surface, plates are pushed apart

As the plates move away from each other, part of them are pulled into the Earth’s mantle

Plates Move Toward Each OtherThis is called Convergent Boundary – these are destructive boundaries since they deform the plates

Continent/Continent

Ocean/Continent

Ocean/Ocean

Convergence creates mountainsMost volcanoes (but not all) form along Convergent boundaries, as one plate is pushed under another and the old crust melts. As two plates rub against one another, a number of small and large earthquakes could occur near convergent boundaries.

http://geology.com/nsta/convergent-plate-boundaries.shtml

Convergence – Moving TogetherTrenches

Mountains

Structural Mountains

Volcanic Mountains

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

Divergent BoundariesMost often takes place at ocean ridges.As the two sides of the crust move away from each other, magma

wells up from the Earth's interior. It then solidifies into rock as it is cooled by the sea, creating new

ocean floor. Causes some volcanoes and earthquakes to form.

http://geology.com/nsta/divergent-plate-boundaries.shtml

The ridges are zones of intense volcanic activity. In addition to forming at the bottom of oceans, these divergent boundaries can also form on continents.

When this happens, a line of volcanoes emerges.

Rift Valley – if the land is above water

Sea Floor Spreading – when the land is below water

Divergence – Moving Apart

The San Andreas Fault is undoubtedly the most famous transform boundary in the world. To the west of the fault is the Pacific plate,

which is moving northwest. To the east is the North American Plate which is moving southeast.

http://geology.com/nsta/transform-plate-boundaries.shtml

Plates Move Side By Side - ***SHIFTINGThis is called Transform Boundary – Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.

San Andreas FaultIs a continental transform fault that runs a length of roughly 1,300 km (800 miles) through California.

Review clip(click on the link above)

ReviewDivergent: Boundary between two plates that are moving apart.Convergent: Boundary between two plates that are pushing together.Transform (Strike-slip): Boundary between two plates that are sliding past one another. *** Causes EarthquakesSubduction Zone: The area where one plate pushes down under another. Volcanoes are often created by this.

As two continental plates move toward each other, what landforms would you expect to see?

A. VolcanoesB. CliffsC. New LandD. Mountains

As two continental plates move toward each other, what landforms would you expect to see?

A. Volcanoes Incorrect

These form at edges of plates or over hot spots

As two continental plates move toward each other, what landforms would you expect to see?

B. Cliffs Incorrect

These are erosional landforms or minor uplift areas

As two continental plates move toward each other, what landforms would you expect to see?

C. New Land Incorrect

Forms when plates move apart

As two continental plates move toward each other, what landforms would you expect to see?

D. Mountains – correct - because 2 continental masses will push into each other and “crumple” the edges to form mountains

Where would you find the newest land on Earth?A. In areas of continental convergenceB. In areas where two ocean plates come

togetherC. In areas where plates are moving apartD. In areas where two plates are sliding past each

other

Where would you find the newest land on Earth?A. In areas of continental convergenceIncorrect

Mountains would form here from existing land.

Where would you find the newest land on Earth?B. In areas where two ocean plates come

togetherIncorrect

You would find trenches in this area.

Where would you find the newest land on Earth?D. In areas where two plates are sliding past each

otherIncorrect

You would find land movement but not new land being formed

Where would you find the newest land on Earth?C. In areas where plates are moving apartCorrect

When plates move apart it is due to magma reaching the surface. When magma cools new land is formed.