The Theory of Plate Tectonics

The Theory of Plate Tectonics

• Essential Questions– What is the theory of plate tectonics?– What are the three types of plate boundaries– How do plate movements relate to various

features of the Earth?

Plate Tectonics• J. Tuzo Wilson observed that there are cracks in

Earth’s surface. He proposed that the lithosphere is broken into separate sections called plates.

• He developed a new theory in 1965 that linked seafloor spreading and continental drift and plates to explain how earth has evolved over time.

• Explains formation, movements, and subduction of the Earth’s plates.

• Framework for understanding mountains, volcanoes, earthquakes, and other landforms and processes of Earth.

Lithospheric Plates

• Topmost solid part of Earth is made of plates – thin layer of crust above thick layer of rigid mantle.

• Plates usually contain oceanic and continental crust.

• 7 major lithospheric plates, named for surface features, many smaller ones

• Pacific is largest plate• Plates move at different speeds and directions

from few mm to several cm per year.

Earth’s Plates

Plate Boundaries

• Where earth’s plates meet

• breaks in the Earth’s crust where rocks slip past each other are called faults

• 3 types of boundaries:– Divergent– Convergent– Transform

Divergent Boundaries

• Where plates move apart – Most at mid ocean ridges where sea-floor spreading occurs.

• Also occur on land – Ex. Great Rift Valley of Africa

Convergent Boundaries• Plates come together – result is a collision• The density of the plates determines which one ends up

on top.• When oceanic meets oceanic, the older crust is denser

and will subduct• Molten rock rises and breaks through surface forming a

string of volcanoes.• In time the volcanoes rise• above the ocean forming • island arcs, Ex. Japan, • Indonesia and the • Aleutians.

Japanese Island Arc

Oceanic and Continental• Oceanic collides with continental – oceanic

is subducted - Continental rises above.

• This pushes up the continental plate forming mountain ranges. Molten rock rises upwards forming volcanoes. Ex. Andes mountains in South America and Cascades of North America.

Andes Mountain

Range

Continental and Continental• Subduction does not take place

• Neither plate is dense enough to sink into mantle.

• Collision squeezes crust into mountain ranges

• Ex. Himalayan mountains

Mountain Ranges

Himalayan Mountain Range

Transform Boundaries

• Where 2 plates slip past each other, moving in opposite directions

• Earthquakes often occur along transform faults. Ex. San Andreas fault in CA

San Andreas Fault

Plate Motions over Time

Movement of Earth’s Plates has changed Earth’s surface over time.

Before Pangaea, other supercontinents formed and split apart over billions of years.

Pangaea formed when Earth’s landmasses drifted together about 260 million years ago.

Then, about 225 millions years ago Pangaea started to breakup.

References• http://www.answers.com/topic/pangaea?cat=technology• http://strangemaps.wordpress.com/2007/12/04/213-pangaea-ultima-cli

mbing-the-mediterrranean-mountains/• http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/g

reatriftvalley.html• http://www.eorc.jaxa.jp/en/imgdata/topics/2004/tp040513.html• http://www.nasa.gov/multimedia/imagegallery/

image_feature_589.html• http://cses.washington.edu/cig/figures/web_pnwtopo1_BIG.jpg• http://user.pix.epodunk.com/WA/Straycat_2679.jpg• http://www.dwarf-cichlid.com/images/Amazon3,map.jpg• http://i.pbase.com/u48/mreichel/upload/

30651589.AndesMountainRangecopy.jpg• http://www.nepalreport.com/files/Himalays-Images/

Mount_himalaya_bhutanQ.jpg• http://www.physicalgeography.net/fundamentals/images/

Earth_relief_map.jpg