Plate Tectonics
The History of Tectonic Theory
Plate Tectonics
Presented by
Doug Winans
Grade Levels 5-8
Continental Drift Hypothesis
Scientists noted geographic fit of continents
1885 Austrian geologist Edward Seuss notes similarities
between plant fossils, and calls the continent
"Gondwanaland".
1910 American physicist Taylor proposes concept of
continental drift to explain formation of mountain belts.
1912, Wegener names the ancient super-continents
"Pangea," based on evidence from geology, climatology and
paleontology.
Supporting evidence for Continental Drift Hypothesis
Geographic fit
Fossils
Mountain Belts
Glaciation
Geographic Fit
Continents appear to fit together like pieces of a puzzle
Fossils
Distribution of fossils
found on both sides of
the Atlantic Ocean,
such as Mesosaurus,
and a prehistoric plant
called Glossopteris.
Mountain Belts
Mountain belts, like the
Appalachians, match across oceans
Glaciation
Striations are grooves
carved in rock by glaciers
Blue arrows show direction
of glacial flow away from
South Pole 
Glacial scoring indicates original location of glaciers
and direction of movement
Continental Drift Hypothesis
• Alfred Wegener
• Meteorologist
• Presented his hypothesis
to other professionals, but
could not explain how
continents drifted
Try to put together Wegner’s
Pangea
Seafloor Spreading
Seafloor Spreading
Development of a New Theory
• Continental drift hypothesis was reexamined in 1960’s
with new information.
• Seafloor Spreading
• Evidence supporting seafloor spreading…
– Paleomagnetism
– Age of Seafloor
Seafloor Spreading
Harry Hess suggests new seafloor is created
at mid-ocean ridges and is destroyed in
deep ocean trenches
Paleomagnetism
• Earth’s magnetic field
reverses approx. every
600,000 years
• As new crust is formed,
normal and reverse
polarities are preserved in
the rock record
• 1963, Vine & Matthews
observe magnetic
anomalies in oceanic crust
• Younger rocks (red) are found near mid-ocean ridges
• Further away, the age of seafloor gets progressively older (blue)
Mechanism for
Seafloor Spreading
• Convection Currents
– As heated magma rises, it moves away at spreading centers pulling
plates apart
– Plates slide over the asthenosphere
– The upper mantle then cools and becomes more dense – sinking at
ocean trenches
Plate Tectonics Theory
John Tuzo Wilson combined the ideas of Continental
Drift and Seafloor Spreading into a new theory…
“Plate Tectonics”
Tectonic Quiz
• What evidence was given for the
Continental Drift Hypothesis?
Glaciation
Fossils
Geographic Fit
All of the Above
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Tectonic Quiz
• Who proposed the Continental Drift
Hypothesis?
Taylor
Hess
Wegner
Seuss
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Tectonic Quiz
• New evidence of “Seafloor spreading” was used
to develop Tectonic Theory. What evidence did
scientists find?
Ancient magnetic reversals in the rocks
Ocean floor dating
GPS measurements
Both A and B above
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Tectonic Quiz
• Who combined Continental Drift and Seafloor
Spreading to produce Tectonic Theory?
Taylor
Hess
“Tuzo” Wilson
Seuss
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Plate Tectonics
History
References
Web Sites:
Pangaea: The Continent
http://www.pangaea.org/wegener.htm
What on Earth is Plate Tectonics?
http://wrgis.wr.usgs.gov/docs/parks/pltec/index.html
Geology Labs: Virtual Earthquake
http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html
Understanding Quakes
http://whyfiles.org/094quake/index.php?g=6.txt
ALFRED WEGENER vs JUST ABOUT EVERYBODY ELSE:
HOW THE CONTINENTS FORMED
http://courses.science.fau.edu/~rjordan/phy1931/WEGENER/wegener.htm
This Dynamic Earth: The Story of Plate Tectonics
http://pubs.usgs.gov/gip/dynamic/dynamic.html
Testing the Sea-Floor Spreading Hypothesis
http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part9.html