Plate TectonicsPlate Tectonics

http://www.learner.org/interactives/dynamicearth/images/new_map.jpg

Tectonic PlatesTectonic Plates

• The Earth’s crust is made of many gigantic plates that move as they ‘float’ on the mantle.

• According to the theory of continental drift, the plates are moving.

• Europe and North America are thought to be moving away from each other 3cm each year.

• Other plates are moving toward each other and some are sliding against each other.

• Wherever plates meet, earthquakes signal their movement.

Tectonic PlatesTectonic Plates

PangaeaPangaea

• Have you ever noticed that the continents look like puzzle pieces?

• In 1912, Alfred Wegener suggested that millions of years ago the continents were all part of one big continent called Pangaea.

http://upload.wikimedia.org/wikipedia/commons/1/16/Wegener_Expedition-1930_008.jpg

Pangaea

http://azgenweb.org/navajo/History/Petrified/Pangaea_continents.png

Continental DriftContinental Drift• Wegener suggested that Pangaea had

broken apart and that the continents had and still are drifting apart.

• This theory is called Continental Drift

• At the time, Wegener’s theory was dismissed as he had no evidence besides the fact that the continents fit together.

http://newpangaea.eu/sitebuildercontent/sitebuilderpictures/Pangaea.JPG

The EvidenceThe Evidence

• Certain fossils of extinct reptiles found only in Africa and South America.

• Fossils of plants and animals found in Antarctica, which is now inhabitable.

• Rocks similar in age and type found along the coasts of continents that fit together.

http://www.lostrivers.ca/points/pangaea.gif

Plate Tectonics TheoryPlate Tectonics Theory• Theory that states that the Earth’s crust is

made up of several large sections called plates.

• These plates are slowly moving, floating on top of the Earth’s mantle.

• Continents drift by riding on top of the plates.

http://www.geography-site.co.uk/pages/physical/earth/images/plates.gif

Sliding-By PlatesSliding-By Plates• When two plates slide against each other,

a fault is formed.

• The plates do not collide or separate; they just slip by.

• Ex) The San Andreas Fault in California.

http://lacreekfreak.files.wordpress.com

Plate CollisionsPlate Collisions

• When two plates collide, one plate usually plunges below into the hot mantle where it heats up and melts.

• This process is called subduction.

http://whyfiles.org/031volcano/images/subduction.gif

Separating PlatesSeparating Plates• When two plates move apart, magma from

the mantle rises up into the crack between the two plates and hardens.

• This forms ridges of new rock.

• Ridges usually form under the ocean but does occur in Iceland also.

http://www.utexas.edu/tmm/npl/mineralogy/blowups/oceanicridge.jpg