Proving Wegener

Mid Ocean Ridge

• The Mid-Atlantic Ridge is part of under-seas Mountain Range known as Mid-Ocean Ridge

• The rocks found on Continents are as old as 3.8 billion years old.

• The oldest rocks in the ocean are only 190 million years old.

• The closer to the Mid-Ocean Ridge the young the rocks became

Mid Ocean Ridge

Mid-Ocean Ridge

Mid-Ocean Ridge

Sea Floor Spreading

• Harry Hess suggested the Mid-Ocean Ridge was a rift.

• Magma wells up forming new ocean floor pushing the old floor further away

• Hypothesis: If the ocean floor is moving then so must the continents be moving

• Hess found the mechanism Wegener had been looking for.

Sea-Floor Spreading

Magnetic Reversal

• Paleomagnetism is when magma cools and hardens into rock and the magnetic orientation becomes permanent.

• Scientist found that the Earth has reversed its magnetic field. North becomes South; and South becomes North

• Scientist discovered that rocks of the same age had the same polarity.

• Scientist discovered a pattern of alternating polarity among rocks called Geomagnetic reversal time scale.

Magnetic Symmetry

• Discovered on either side of the Mid-Ocean Ridge identical pattern of magnetic reversal.

• Using this data and geomagnetic reversal time scale were able to date the ocean floor.

• Found the age of the sea floor was also symmetrical.

• The further from the Mid-Ocean Ridge on either side the older the rocks became

• This further supported Hess’s Theory of Sea Floor Spreading

Magnetic Reversal

Wegener Redeemed

• Scientist found the same magnetic reversal on Land as on the Ocean Floor

• Scientist reasoned that Sea Floor Spreading was the missing mechanism that forced the continents to move.

• Wegener’s idea of Continental Drift becomes the Theory of Plate Tectonics.

Tectonic Plate Boundaries

Plate Boundaries

Divergent Plate Boundaries

Convergent Plate Boundaries

Transformed Plate Boundaries