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What????
The DeLorean “Time Machine”
Drifting Apart:
The Theory of “Continental Drift”
What’s the meaning of “Continental
Drift”?
• Earth’s crust is constantly moving
- horizontal
- vertical
• Crust is drifting on top of the mantle
(asthenosphere)
• Two types of crust
- Continental and Oceanic
• Shape and location of the continents and
oceans have changed over millions of years
(Constructive & Destructive Forces)
Alfred Wegener
• He hypothesized about 300 MYA the Earth had
only one giant continent called Pangaea
(meaning “all lands”)
• Published The Origin of Continents and Oceans
in 1915
• Evidence supporting the theory:
-
Puzzle-Like Fit
Fossil records
Rock sequences
Climates and changing polar regions
Mountain Ranges
Alexander Du Toit
Proposed that 200 M.Y.A., Pangaea broke
up into two supercontinents:
• Gondwanaland
- S.A., Africa, Antarctica, Australia, India
• Laurasia
- N. A., Eurasia (Europe and Asia)
Pangaea was surrounded by a sea called
Panthalassa
Evidence for Continental Drift
Evidence #1: Puzzle-Like Fit
Matching coastal lines fit together like a
jigsaw puzzle
-
South America & Africa
Evidence for Continental Drift cont.
• Evidence #2: Fossil Clues
Similar fossils found on several different continents
Separation by oceans suggests that the continents
were once connected
-
Glossopteris: fern (southern continents)
Cynognathus: land reptile (S.A. & Africa)
Lystrosaurus: land reptile (Africa, Antarctica, & India)
Mesosaurus: freshwater reptile (S.A. & Africa)
Evidence for Continental Drift cont.
Evidence #3: Rock
Types
Similarities in rock types
found in S.A., Africa,
India, Antarctica, and
Australia
Paleomagnetism
- Study of the
magnetism of ancient
rocks and sediments
Continental Drift Evidence
Evidence #4:
Climate Clues
• Continental ice
sheets and glacial
markings in South
Africa
• Fossils of tropical
plants found in
Spitsbergen (small
island north of
Norway)
• Suggests
movement from the
equator and the
poles
Continental Drift Evidence
Evidence #5: Mountain Ranges
• Similar mountain ranges
-
Argentina and South Africa
Theory Rejected
• Wegener could not explain the forces
that push or pull the continents
• Geologists rejected his theory of
continental drift
• Lacked information on formation of
mountains and continents
• Then new evidence was discovered…
• As a Jr. Geologist, what kind of
forces (give examples) do you
“infer” could be used to “push and
pull” the continents around???
Can you G.R.A.S.P.
Continental Drift?
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