Continental Drift- The Theory

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Continental Drift-The Theory
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The Earths crust is broken into about 12 rigid
plates, which slide over a semi-molten plastic
layer of the mantle.
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Tectonic Plates on Modern Earth
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The material making up the plates can be
divided in two types i. Oceanic crust ii.
Continental crust
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The History of the Theory of Continental Drift
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1600 - development of a comprehensive world map
(missing details of some continents such as
Australia and Antarctica). .
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• 1620 - Francis Bacon noted the similarity of the
  shape of the continents on either side of the
  Southern Atlantic Africa and South America

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1858 - Antonio Snider developed a theory that
when the Earth cooled from a molten mass
continents formed only on one side. This created
instability causing the Americas to be pulled
away from the rest of the continents.
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1879 Sir George Darwin said that the Pacific
Ocean was the scar left behind when the Moon
pulled away from the Earth. After this happened,
the continents moved to create a balanced
planet. .
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1924 - Alfred Wegener developed the theory of
Continental Drift to explain the similarities of
rocks, fossils and other geological structures
on either side of the Atlantic. At this time it
was accepted that the continents sat like
icebergs on the mantle. Wegener suggested as well
as moving up and down in the mantle, continents
could move sideways in the mantle. -Wegener
was a meteorologist and his theory was not well
accepted. (He died on an expedition in Greenland
collecting ice samples).
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Continental Puzzle Time
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• End of Day 1

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Continental Drift Evidence

• Geographic fit of South America and Africa
• Fossils match across oceans
• Rock types and structures match across oceans
• Ancient glacial features

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Continental Drift Evidence
Tight fit of the continents, especially
using continental shelves.
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Continental Drift Evidence
Fossil critters and plants
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Continental Drift Evidence
Correlation of mountains with nearly identical
rocks and structures
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Continental Drift Evidence
Glacial features of the same age restore to
a tight polar distribution.
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Earth 200 million years ago