Theory of Plate Tectonics

Oceans 11

But first…a little about the internal structure of the Earth

A Brief look Earth’s 2 major layers

Earth’s Internal Structure

• Earth can be divided into 3 main layers:• Crust (outside of Earth)• Mantle • Core (very inside)

Earth’s Crust• Crust is the outermost layer.• Two Parts of Crust:

– Continental crust• Mainly granite• Up to 75km thick• Density 2.6g/cm3

– Oceanic crust• Made up of basalt rock (type of volcanic rock)• Up to 8 km thick• Density 3.0g/cm3

The Mantle• The mantle is the next layer.• This zone is about 2900km thick and makes up

great 82% of Earth’s volume.• Fragments of the mantle have been brought to

the surface by volcanic eruptions.

Earth’s Core• Earth’s core is extremely hot – hot as the

sun!• Divided into two parts.

– Outer Core• Liquid iron and nickel

– Inner Core • Solid iron

Now let’s look at the Theory of Plate Tectonics…

Plate Tectonics – brief history• 1912

– Alfred Wegener, German geophysicist and meteorologist

– Wegener thought that all landmasses formed one supercontinent approximately 225 mya “Pangaea” meaning all earth.

Wegener’s research:• Geologic record (rock strata)• Fossil record• Climatic record of continents• A KEY FINDINGS:

– Southern America & Africa have many similarities

• Large coal deposits

Resistance…• Wegener was met with a lot

of skepticism from other scientists and the church.

• 1950 to 1960’s – Geologic Discoveries:

• Similar fossils on each continent

• Same age rock on coast lines• It wasn’t until the 1960’s

that Wegener’s theory was accepted and coined Theory Plate Tectonics

Animation of Continental Drift

• http://education.sdsc.edu/optiputer/flash/pangea_4.htm

PANGEA

Definition of Plate Tectonics• Tectonic – Greek meaning “building” or

“construction”• Refers to the configuration of Earth’s crust

as a result of internal forces.

Plate Tectonic Processes• Include:

– Upwelling of magma– Crustal plate movements– Sea-floor spreading– Subduction of crust– Earthquakes– Volcanic activity– Warping, folding and faulting of crust.

Earth’s Plates• Plates are made up of:

– Continental crust– Oceanic crust

• These plates float upon the moving asthenosphere.

• Plates move 1 to 19 cm per year– Movement of plates are a result of convection

currents in the asthenosphere– http://education.sdsc.edu/optiputer/flash/convection.htm

Earth’s Plates

• What do you notice about the relationship between volcanoes(red), earthquakes (yellow) and location of plate boundaries?

3 Main types of Plate Boundaries

1. Divergent plate boundary2. Convergent plate boundary3. Transform plate boundary

Divergent Plate Boundaries• Plates separate (move away from each other)• Almost always occurs between two ocean plates. • When ocean plates separate, new crust is formed through the

upwelling of magma. This is called sea-floor spreading.– http://education.sdsc.edu/optiputer/flash/seafloorspread.htm

– Mid-oceanic ridges – http://www.planetseed.com/files/flash/science/features/earth/

livingplanet/plate_boundaries/en/index2.html?width=570&height=475&popup=true

• Iceland, "the land of fire and ice", is being split by an oceanic ridge that surfaces to create an oceanic island (left and below) in the North Atlantic Ocean.

• Red triangles show Iceland's active volcanoes, including Krafla. Reykjavik is Iceland's capital.

Divergent Plate Boundaries• Something

interesting!!!• Great Rift Valley in

Africa• A continental plate is

breaking up!• Convection currents

under the crust are pulling this area apart!

• http://www.youtube.com/watch?v=w7Y2R4KBwvo

Convergent Plate Boundaries• These plate boundaries can occur between:

– Oceanic and Continental plates• “Subduction Zones”• http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_boundaries/en/index2.html?

width=570&height=475&popup=true

– Continental and Continental plates• Mountain building• http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_boundaries/en/index2.html?

width=570&height=475&popup=true

Transform Plate Boundaries• These are where plates move side-to-side.• Trigger earthquakes• http://www.planetseed.com/files/flash/science/features/earth/livingplanet/

plate_boundaries/en/index2.html?width=570&height=475&popup=true

Your Task • Complete the “checking your

understanding” questions and hand in.• Complete the Plate Tectonic Map Activity