Download The Theory of Continental Drift

Formation of continental crust
• Buoyant Material rises to the surface of a
molten Earth,
• Continental (Felsic) material is less dense,
more buoyant, therefore rises and “floats
Higher”
3 bya
2.8-2.5
bya
1.6-1.2
bya
1.2 bya to
700 mya
Continental Drift
• Proposed by Alfred Wegener in 1912
• Hypothesis: 250 million years ago, all of
the continents were combined into one
super-continent called “Pangaea”, (all
land).
• The continents gradually drifted apart to
where they are today
Alfred Wegener
• 1880-1930, German meteorologist
• Noticed that South America and Africa look
as though they could fit together like pieces
of a puzzle.
• proposed the hypothesis of continental drift
in "On the Origin of Continents and
Oceans" (1912)
• Died while crossing the Greenland ice cap
in 1930, exploring.
Evidence for
Wegener’s
hypothesis.
“Puzzle Pieces”
• A. Continents look
like they could be part
of a giant jigsaw
puzzle
• NOTE: Shorelines
don’t match perfectly,
but the continental
shelves do.
Distribution of Fossils
• B. Plant and
animal fossils
found on the
coastlines of
different
continents
Tie-in to
Sequence of Rocks
• C. Same rock
patterns found in
South America, India,
Africa, Antarctica and
Australia
Geological Evidence for
Continental Drift
• D. geological
matches
– mountain belts
(AppalachiansCaledonians)
– age similarities
(matching
Archean cratons)
–
–
stratigraphic similarities, matching
layers of rock (e.g., Nova Scotia and
Morocco)
igneous provinces, chemical imprints
(Mesozoic basalts, Precambrian
anorthosites)
Ancient Climates
• E. Tropical plant
remains (coal
deposits) found in
Antarctica
• E(2). Glaciation in
Africa, South
America, India, and
Australia during the
same time
Paleoclimate evidence
Glacial
striations
Ice sheets covered big areas of southern hemisphere
~ 220-300 million years ago
E(3). Climate Evidence
 Coal deposits and fern
fossils in Antarctica
 Glacial deposits in
India, S. America,
Africa, Australia
hint: These locations
must have once been
at a different latitude
(further north or
south!)
Problems With The Hypothesis
• No mechanism for movement of
continents. What force could possibly drive
them?
• Wind and water currents could possibly
move fossils. Some animals could migrate
/ swim.
• Biblical Stories explained marine fossils on
mountain peaks, as well as the existence
of tropical fossils in Antarctica.
• Theory was not accepted by scientists.
• Glacial evidence and geologic matches,
however, were stumpers.
Wegener’s
Hypothesis
Confirmation of Continental
Drift
• World War II technology
– mapping the ocean floor with sonar
– Discovery of the match of continental shelves.
They matched up better than previously
thought.
• Worldwide Standardized Seismic Network
1963-
What do you notice?
Worldwide Standardized Seismic Network
Discovery of Sea-Floor
Spreading
Sea-Floor
Spreading
Seafloor Spreading:
What does this mean for the
evidence of the theory?
Now we have a theory.
What is the difference between
a theory and a hypothesis?
• A hypothesis is an idea, an educated
guess, or a possible solution derived from
logic or common sense.
• A theory is an explanation that fits ALL of
the facts, observations, and data.
• Scientists realized there was a relationship
between seafloor spreading, volcanic
activity, earthquakes, mountain formation,
mid-ocean ridges, the continental shelves,
and deep ocean basins.
The Plate Tectonics Model