The Theory of Plate Tectonics

• Earth’s crust is made of many plates• These plates move as a result of

convection in the mantle• Earth’s surface is constantly being

reshaped by these movements• Earthquakes, volcanoes, rifting and

mountain building all result from the process of plate tectonics.

“ Continental Drift”

• Alfred Wegner – German scientist

• Continents have not always been in their present locations

• All continents were once part of a super-continent called Pangea

• Also only one great ocean called Panthalassa

EVIDENCE TO SUPPORT CONTINENTAL DRIFT

• Puzzle-Like fit of the continents

• Fossil Evidence

• Matching Geologic Features

• Evidence of Climate Change

Wegener’s evidence for Continental drift

• Fossils of ferns and reptiles are the sameon many different continents.

• Evidence of Glaciers in areas that are now tropical.

• Same types of rocks layers are the same on continents that are separated by an ocean.

• The coastlines of Africa and South America fit together like puzzle pieces.

EVIDENCE TO SUPPORT CONTINENTAL DRIFT

• Puzzle-Like fit of the continents

• Fossil Evidence

• Matching Geologic Features

• Evidence of Climate ChangeSo….. If Alfred Wegner had all of this evidence to support his theory of Continental Drift, why did many scientists not accept his idea? What was he missing?

Convection Currents

The Movement of Plates

CONVECTION• Convection is overturning motion and the

transfer of heat resulting from heating and density differences

• Lithospheric plates move as a result of convection in the mantle

• Convections cells in the asthenosphere rotate slowly over millions of years.

• Because the convections cells rotate in different directions, the plates move in different directions also

• Convection can also be used to explain the cause of wind and ocean currents

Convection in the Mantle

Early Earth and Plate Tectonics

Earth's Future

Earth 100 Million Years From Now

Plate Boundaries

• Where two plates meet a plate boundary is formed.

• What happens at a plate boundary depends on the direction each plate is moving and the density of each plate

• Earth’s surface is constantly being reshaped by these movements

• Earthquakes, volcanoes, rifting and mountain building occur at or near plate boundaries.

• Plate movements also cause forces that affect areas along the boundary and within the plate itself.

Type of Plate Boundaries

• Plate boundaries are classified into three main groups based upon the relative direction of movement– Convergent Plate Boundary: plate move

towards each other– Divergent Plate Boundary: plate move apart– Transform Boundaries: plate slide past each

other (side by side)

Convergent Boundaries

• There are three types of convergent boundaries classified the type of crust involved:– Continent to continent convergence– Ocean to continent convergence– Ocean to ocean convergence

The Himalayan Mountains, Including Mt. Everest, formed as a result of the convergence of the Indian and Asian Plates

Continental-Continental boundaries

Island arc volcanoes and deep ocean trenches form at ocean crust to ocean crust convergent boundaries

Oceanic-Oceanic boundaries:

Ocean crust to continental crust convergent boundary. Because oceanic crust is more dense than continental crust, the ocean crust is subducted

Continental-Oceanic boundaries:

Subduction Zones

• When two plates of different densities collide at a convergent boundary, the denser plate is driven under the less dense plate forming a subduction zone

• Magma is generated in the subduction zone resulting in the formation of volcanic arcs.

Transform Boundaries

• When two plates slide past each other a transform boundary is formed.

• Earthquakes are common along transform boundaries because the plate do not slide smoothly past each other

The San Andreas fault is an example of a Transform Boundary

Divergent Boundaries

• When two plates move apart a divergent boundary is formed.

• Mid-Ocean Ridges and Rift Valleys form at divergent boundaries

New ocean crust is created at mid-ocean ridges.

These are also referred to as spreading centers

Iceland is a volcanic island that has formed on top of a Mid- Atlantic ridge

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AC

B

ED

FG

H

J

Identify the types of boundary and geologic landforms

1 32

K

A B

Convection Current

A

Convection Current

BConvection

CurrentA

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December 26, 2004 -An Earthquake 9.0 on the Richter hit Indonesia creating a massive tsunami that killed over a quarter of a million people

A B

Convection Current

A

Convection Current

BConvection

CurrentA