PLATE TECTONICS: The Unifying Theory of Geology

JIGSAW-LIKE FIT OF CONTINENTS

Has been described since 1600’s

Alfred Wegener – Austrian Meteorologist

Wegener thought that the continents were once all together in a single super-continent that he named Pangaea.

Pangaea subsequently broke apart and the continents “drifted” into today’s positions

Pangaea

EVIDENCE FROM

GLACIERS

Other Climate Evidence

EVIDENCE FROM FOSSILS

EVIDENCE FROM GEOLOGIC STRUCTURES

CONTINUITY OF MOUNTAIN BELTS ACROSS CONTINENTS

As if one had torn a piece of newspaper in half – Could you read the lines if the pieces were put back together?

To discover how Plate Tectonics works we must study the Earth using several fundamental physical principles & properties:

1) Seismic Waves2) Gravity3) Isostacy4) Magnetism

1) SEISMIC WAVES & EARTHQUAKES

1) SEISMIC WAVES & EARTHQUAKES

a) Apply a force (Stress)b) Material Deforms (Accumulates Strain)c) Material Ruptures d) Returns to original shape around the fracture (Elastic Rebound)

a) Fracture about which the two sides move is called a Fault.b) Elastic Rebound releases energy waves called Seismic

Waves or Earthquake Waves.c) Seismic Waves propagate through rocks and cause

them to “shake”, producing Earthquakes.

HOW DO WE STUDY SEISMIC WAVES ?

A Seismograph

Seismogram

There are different types of Seismic Waves!

1) P-Waves: Compression Wavesfastest waves, arrive at a seismograph station first.Cause compression – expansion in rocks.

2) S-Waves: Shear Wavessecond highest velocity, arrive at seismograph second.Cause shear – rocks move at right angle to direction of wave propagation .

3) Surface Waves: Complex motionsSlowest waves, arrive at a seismograph station last.Create rolling motions, causing the most shaking

Seismic WaveMotions:

1) P- Waves

Seismic WaveMotions:

2) S- Waves