plate tectonics

Plate TectonicsLiz LaRosa for use with my 5th Grade Science Class

http://www.middleschoolscience.com 2009

Earth’s LayersThe Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed.

This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle.

The Crust

• Outermost layer• 5 – 100 km thick• Made of Oxygen, Silicon, Aluminum

The Mantle• Layer of Earth between

the crust and the core• Contains most of the

Earth’s mass• Has more magnesium

and less aluminum and silicon than the crust

• Is denser than the crust

The Core• Below the mantle

and to the center of the Earth

• Believed to be mostly Iron, smaller amounts of Nickel, almost no Oxygen, Silicon, Aluminum, or Magnesium

earth's layers

Tectonic Plates

Plate Tectonics

• Greek – “tektonikos” of a builder• Pieces of the lithosphere that move around• Each plate has a name• Fit together like jigsaw puzzles• Float on top of mantle similar to ice cubes

in a bowl of water

plate tectonics

Continental Drift

http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml

Alfred Wegener 1900’sContinents were once a single land mass that drifted apart.

Fossils of the same plants and animals are found on different continents

Called this supercontinent Pangea, Greek for “all Earth”

245 Million years ago

Split again – Laurasia & Gondwana 180 million years ago

continental drift

Evidence of Pangea

Sea Floor Spreading

Sea Floor Spreading

• Mid Ocean Ridges – underwater mountain chains that run through the Earth’s Basins

• Magma rises to the surface and solidifies and new crust forms

• Older Crust is pushedfarther away from the ridge

sea floor spreading

How Plates Move

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

Different Types of Boundaries

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

plate boundaries

Divergent Boundary

• Plates move apart• Constructive plate boundaries – where new

oceanic lithosphere is created• Forms oceanic ridges in oceans• Forms rift vallies in continents

Divergent Boundary – Arabian and African Plates

Arabian Plate

African PlateRed Sea

Divergent Boundary – Iceland

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

Divergent Boundary - Oceanic

http://www.geology.com

Oceanic ridge

Divergent Boundary - Continental

http://www.geology.com

Rift vally

Convergent boundary

• Destructive plate margins• Leading edge of one plate is bend downward

and slides beneath the other• subduction zones are where one oceanic plate

slides beneath a second plate

Convergent Boundary – Indian and Eurasian Plates

Indian Plate

Eurasian Plate

Convergent Boundary – Oceanic & Continental

http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Oceanic plate is more dense and sinks below the continental plate which is less dense and floats on top.

Denser oceanic plate sinks to asthenosphere and begins to melt.

Magma is less dense than surrounding rock and rises, sometimes causing volcanic eruptions.

Convergent Boundaries - Continental

http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Continental lithosphere is buoyant and doesn’t sink to great depth.

Complex mountain ranges are formed.

Appalachian, Alps, Himalayas, and other mountain ranges were formed this way.

Convergent plates - oceanic

• One plate sinks beneath the other causing volcanic activity similar to oceanic – continental plate margins

• Volcanic island arcs are newly formed land masses forming arc shaped volcanic islands.

Transform boundary

• Plates grind past each other without destroying the lithosphere

• Most are located within ocean basins.• A few, like the San Andres Fault, cut through

continental crust

Transform Boundary – San Andreas Fault

www.geology.com

Slab Pull• Slab pull- old oceanic crust, which is cool and

dense, has sunk under another plate into the asthenosphere which pulls the trailing lithosphere along.

Ridge Push

• Ridge push- results from elevated oceanic ridge system and causes oceanic lithosphere to slide down the sides of oceanic ridge.

Convection• Hot plumes of rock are flowing upward in

mantle convection.• Hot plumes sometimes show themselves on

earth’s surface as hot spots and volcanoes.

Review

• Name the 3 main layers of the Earth• What is a tectonic plate?• What was Pangea?• What is Sea-Floor spreading?• Name the three different types of plate

boundaries and one location on Earth for each one

Resources

• This powerpoint was adopted from middleschoolscience.com by Ms. Glass on 9/07/12

• Video clips were found on youtube and incorporated