A. HISTORY OF THEORY

1. Alfred Wegener (1912), German climatologist and geophysicist, suggested idea of continental drift and super-continent Pangaea (333; all lands): based on fit of continents (316), fossils (316), fit of ancient mountain ranges (318), and ancient glaciation (318).

2. Hess & Dietz (early ‘60s) suggested sea-floor spreading based on ocean-floor topography.

3. Vine & Matthews (1963) discovered magnetic strips on ocean floor are symmetrically distributed about mid-ocean ridges. These were attributed to the continuous production of lava that recorded the orientation of Earth’s magnetic field at the time of eruption. 333

4. Research ship Glomar Challenger - discovered that the age of the sea-floor increases with distance from mid-ocean ridge. This finding helped to confirm sea-floor spreading. New term - plate tectonics.

5. The distribution of earthquakes outlined the margins of plates (‘68); deep earthquakes defined subduction zones. 334

6. New tests - plate motion has actually been measured by GPS.

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