Transcript Chapter 8: Major Elements

Continental Drift
Alfred Wegener (1912)
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First serious proponent
Took time to look carefully at
the data & carefully study it
Many scientists have ideas
and don't follow up
Many geologists were more
familiar with the data, but
couldn't bring themselves to
believe it
Wegener looked at the facts
in the perspective of the
theory & looked for
consistencies
Alfred manning the weather station,
Greenland - 1913
Fit of the Continents
A modern view than Wegener’s uses 1000 or 2000 m
isobath as estimate of edge of continental crust
Fit of Structural Elements
Pennsylvanian (300 Ma) Glaciation
Glacial striations in
bedrock, South Australia
Pennsylvanian (300 Ma) Glaciation
Arrows indicate ice
movement directions
Using present continental locations
Pennsylvanian (300 Ma) Glaciation
Arrows indicate ice
movement directions
Using pre-drift continental locations
Fossil Evidence
Glossopteris: an
ancient seed fern
(200 Ma)
Distribution of
Glossopteris
fossils
Fossil Evidence
Distribution of
Mesosaurus fossils
Mesosaurus couldn’t
swim in open ocean
Paleomagnetism
The Earth as a dipole
Magnetic declination and inclination
Paleomagnetism
Magnetization of volcanic rocks and sediments
Paleomagnetism
“Polar Wandering” curves
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In spite of this data, the theory of continental drift
died off in the 1950s, mainly because the
geophysicists could not find an adequate
mechanism to move the rigid crust and mantle