Transcript Plate Tectonics Tectonics

Plate Tectonics
Tectonics refer to the deformation of Earth’s
crust and results in the formation of structural
features such as mountains
Continental drift: An idea
before its time
Alfred Wegener
• Proposed hypothesis in 1915
• Published The Origin of
Continents and Oceans
Continental drift hypothesis
• Supercontinent Pangaea (meaning “all
lands”) began breaking apart into smaller
continents about 200 million years ago
Pangaea approximately 200
million years ago
Ocean opens between rigid plates
As the plates moves, the distance between two cities on the same
Plate, New York and Denver, for example, remains relatively
constant while the distance between New York and London is
continually changing
Continental Drift Evidence
Geometry of continental margins
Similarity of rocks and structures
Correlation of glacial deposits
Distribution of fossils
Paleomagnetism and “polar wander”
Topography and other features of the seafloor
South America and
Africa fit almost
perfectly.
Not at the shoreline,
but at the true edge
of the continental
margin (at the
bottom of the
continental slope).
 South America
and Africa were
joined in the past and
split apart when the
Atlantic Ocean
opened
Paleozoic glacial deposits
and features are common
among the now separate
southern continents…
But they are now near the
equator! Huh?
Also, the direction of ice
movement is from what is
now the sea towards the
interiors! Huh?
These observations only
make sense if the southern
continents were once joined
and were at the south pole!
The great debate
Objections to drift hypothesis
• Inability to provide a mechanism capable
of moving continents across globe
• Wegner suggested that continents broke
through the ocean crust, much like ice
breakers cut through ice
The great debate
Continental drift and the scientific
method
• Wegner’s hypothesis was correct in
principle, but contained incorrect details
• For any scientific viewpoint to gain wide
acceptance, supporting evidence required
Plate tectonics: The new paradigm
More encompassing theory than
continental drift
Mix of ideas that explained motion of
Earth’s lithosphere by subduction and
seafloor spreading
Plate tectonics: The new paradigm
Earth’s major plates
• Associated with Earth's strong, rigid
outer layer
– Known as the lithosphere
– Consists of uppermost mantle and overlying
crust
– Overlies a weaker region in the mantle called
the asthenosphere
Basal tractions drive plate motions