Plate Tectonics

A Whole Lot of Shakin’ Goin’ On

What are tectonic plates?•Tectonic plates are pieces of the crust that move around on top of the mantle. •There are ten major tectonic plates.•The tectonic plates form a “jigsaw puzzle” like structure.

http://www.acmecompany.com/stock_thumbnails/11997.world_plates.gif

Tectonic Plates

Mapping the Earth’s Interior

• Scientists have gained the majority of their knowledge about the inner parts of the Earth from earthquakes.

• Earthquakes produce seismic waves which travel through the Earth at different speeds, depending on the material they pass through.

• Seismographs measure the difference in the waves’ arrival times, which let scientists know the density of the material the waves passed through.

Restless Continents

•If you were to remove all of the oceans from the Earth and move the continents together, they would fit together like a jigsaw puzzle.

•Is this a coincidence? NO!

•If you try to put them back together, there’s only 1% that doesn’t fit right!

http://www.scarborough.k12.me.us/wis/teachers/dtewhey/webquest/nature/images/pangaea%20fitting%20together.gif

Wegener’s Theory of Continental Drift

• It is the theory that continents can drift apart from one another and have done so in the past.

• Wegener’s proof was fossils of the same plant or animal found on both sides of the Atlantic Ocean. Many of these species couldn’t make it across the ocean.

• Continental drift also explained similar glacial patterns found on different continents.

http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_pics/F1.4.gifhttp://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part5.html

Evidence of Pangea

Wegner and Continental Drift

The Breakup of Pangaea• Wegener thought that all of

the continents of today were once joined together about 245 million years ago in a single supercontinent called Pangaea.

• Around 180 million years ago, Pangaea split into two big pieces, called Laurasia and Gondwana.

• 65 million years ago, Laurasia and Gondwana split into the current continents.

http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part2.html

The Breakup of Pangaea

Sea-Floor Spreading

• Many scientists did not accept Wegener’s theory. Wegener could not explain what force caused the continents to drift apart.

• Sea-floor spreading answers that question. Sea-floor spreading is the process by which new oceanic crust is created (by magma) as older materials are pulled away.

• The crust increases in age the farther it gets from the mid-ocean ridge formed by the process.

Sea Floor Spreading

Sea-Floor Spreading

http://www.shenet.org/middle/acadia/bmoses/bm%20images/seafloor%20spreading.jpghttp://hal.physast.uga.edu/~jss/1010/ch14/ridge.jpg

Seafloor Spreading

Theory of Plate Tectonics• The Theory of Plate Tectonics replaced

Wegener’s theory. • This theory states that the Earth’s crust

is divided into tectonic plates that move around on top of the mantle.

http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part12.html

How Plates Move

http://pubs.usgs.gov/gip/dynamic/unanswered.html

Tectonic Plate Boundaries

• Convergent – Occurs when two tectonic plates push into one another. The three types of convergent boundaries are continental/continental, continental/oceanic, and oceanic/oceanic.

• Divergent – Occurs when two tectonic plates move away from one another. Mid-ocean ridges are the most common divergent boundary, but they can also be found on continents.

• Transform – Occurs when two tectonic plates slide past one another horizontally. The San Andreas Fault is a good example

of a transform boundary.http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part13.html

What happens when these plates move?

• Convergent plate boundaries form mountains.

• Divergent plate boundaries cause volcanoes.

• Transform plate boundaries cause earthquakes.

Tectonic Plate Boundaries

Different Types of Boundaries

http://pubs.usgs.gov/gip/dynamic/understanding.html

Tectonic Plate Boundaries

Plate Tectonics

Tracking Plate Motion

• The speed at which plates move depends • the type and shape of the plate• the way it interacts with the plates that surround

it.

• The movement is generally so slow that you can’t see or feel it. It is measured in centimeters per year.

• The exception is the San Andreas Fault, which moves in jerks and jolts. These jerks and jolts cause earthquakes.

• Scientists use the Global Positioning System (GPS) to measure the movement of the tectonic plates. Radio signals are sent from the Earth to orbiting satellites, measuring the distance between the two. Over time, the distances change slightly.

http://www.geologie.ens.fr/~vigny/images/gps-cours3.jpg