Acceptance of vertical uplift, but not horizontal motions

• Da Vinci (1508), recognition Marine fossils on land- uplift
• Hutton’s (1795) ideas of uplift and erosion
• Darwin’s (1830’s) observation of Chilean coast uplift by earthquakes

Wegener's (1915) continental drift hypothesis: impressive but evidence ignored

• Observations on the shape of the continents
• Paleontological evidence
• Evidence for glaciation
• Matching Mountain Ranges across N. Atlantic
• Pangea - the Supercontinent
• The driving force???

Revival of Horizonatal motions in 1950’s: The Earth's Magnetic field

• Bipolar nature of the field
  • Not due to permanent magnetism
  • Temperatures in the Earth too high
  • Origin in the molten outer core - geodynamo
  • Minerals as recorders of the magnetic field
  • The Curie Point-580° C
  • Reversals of the magnetic polarity

Polar Wander curve for the continents:Studies of Paleomagnetism

• Direction of the magnetic field
• Magnetic inclination - magnetic latitude of the rock
• Direction and inclination allow finding the poles at the time
• Apparent motions of the pole
• N. American and European data for the past 600 m.y.

Studies of the ocean floor - Glomar Challenger (1960's)

• Discovery of mid-ocean rifts, ocean floor topography Overhead-10
• Sea floor basalts not older than 200 m.y.
• Sea floor sediments < 300 m.thick and < than 200 m.y.
• Progressively older sediments from the rift
• Oceanic crust is a young feature on the planet
• Sea floor spreading (1962) - prelude to Plate Tectonic Theory