Plate Tectonics Continental Drift

Continental Drift Hypothesis Proposed by Alfred Wegener All continents were at one time connected Formed supercontinent – Pangaea Surrounded by one ocean – Panthalassa Began breaking apart ~200 mya

Evidence Similarities in coastlines

Evidence Fossil remains (Mesosaurus)

Evidence Geological evidence

Evidence Change in climatic patterns

Continental Drift Hypothesis Rejected – no propelling force Wegener died in 1930 in Greenland Idea was shelved until 1960s when new evidence was introduced

Seafloor Spreading Discovered while mapping Mid-Atlantic Ridge: rocks closer to ridge younger (180 million years old) than those further away (4 billion years old)

Harry Hess Determined that ocean floor must be moving away from ridge; magma welling up through a rift in ridge creating new floor. Could this be propelling force? Again, no proof!

Here’s the proof!!! Paleomagnetism

Paleomagnetism Iron-bearing minerals in rocks can become magnetized, solidify, and align with magnetic north (normal polarity) Throughout history, there have been times when magnetic orientations have been to the south: magnetic reversals (reversed polarity)

These magnetic orientations mirror each other on either side of the ridge proving that the seafloor is spreading

Proof! If the ocean floor is moving, the continents are also moving. Wegener’s proof of Continental Drift!!!