THE THEORY OF PLATE TECTONICS

INB Page 81

EQ: Explain the evidence supporting the theory of plate tectonics.

CONTINENTAL DRIFT & PLATE TECTONICS

• 1912: Alfred Wegener• Proposed theory of Continental Drift

• Suggested millions of years ago there was only one supercontinent, Pangaea, that pulled itself apart

• Eventually formed the landmasses of today

• Very little evidence to support this theory when first proposed

CONTINENTAL DRIFT & PLATE

TECTONICS

• 1960s: Theory of Plate Tectonics• Continental drift theory was revised as new evidence appeared

• Revised theory suggests:

• lithosphere (outer layer of Earth’s crust) is made of many separate plates

• These plates float on underlying layer of mantle (asthenosphere)

• Plates move incredibly slowly in relation to each other

• Creates 3 types of plate boundaries

• Convergent

• Divergent

• Transform

• Activity at the boundaries creates mountains, earthquakes, volcanic activity, and ocean trench formation

BOUNDARY TYPES

EVIDENCE IN SUPPORT OF THEORY OF PLATE

TECTONICS

• Fit between coastlines

• Paleontology showing distribution of fossil species

• Magnetic stripes in ocean floor indicating spreading

• Sonar images of ocean floor