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