•When examining sedimentary rocks from the paleoclimatic reconstructions, Wegner
found that the distribution of the polar positions were very different in the past
compared to now. Hence, he hypothesized that in the past continents had moved.
•Skepticism about Continental Drift
oWegner believed that the continents ploughed through he oceanic crust,
compiling mountain ranges in the front. Knowing the strength of rocks at the
time, this was a bad explanation.
oWegner also proposed that based on a combination of two forces, the
centrifugal force and gravitational forces that continental drift was possible.
HOWEVER, through carful calculations it was shown that these forces are
way too small to account for the movements of continents.
•The study of the sea-floor and geophysical research (rock magnetism) renewed
interest in continental drift in the 40s and 50s.
•Geophysical Research- When rocks are formed they have within them magnetite
(cooled basaltic lava flow or other metallic minerals) that point towards the poles
and once cooled get frozen in time. This frozen “compass needles” tell us where the
magnetic poles were at the time of rock formation. It was originally believed based
on the results, that the poles were moving ver time. Now, however its believed that
the continents (the rocks) were the ones moving.
oAssuming there was only one pole, and lets take out the atlntic ocean in
between North America and Europe....then the polar wandering paths for
Europe and North America would be the EXACT same. Hence, this suggests
that at one time Europe and NA were both joined together (supercontinent)
and that over time the Atlantic ocean formed in between.
•More Evidence – Rock types matches: boulders in South America have been traced to
sources in Africa. Rock Matches show continents were at one point together.
•Pangea split up to 200 million years ago, but evidence shows that the continents
have been moving for up to 2 billion (some say 4 billion) years now.
What is Sea Floor Spreading?
•Harry Hess suggested that the sea floor was spreading; totally opposite idea to
Wegners (that the sea floor was still while the continents moved through them)