Name: ___________________________________ Period: ___
Continental Drift and Plate Tectonics
Continental drift: An idea before its time
Alfred ________________
First proposed his continental drift hypothesis in _________________
Published The Origin of Continents and Oceans
Continental drift hypothesis
Supercontinent called __________________began breaking apart about 200 million
years ago
Continental Drift
Continental Drift provides an explanation for why the same _______________________ and
_______________________ species are found in different parts of the world.
It would have been impossible for many of these species to have crossed the entire
__________________________________ Ocean.
Also, similar types of _______________________ have been found on different continents.
Continental Drift
Continental drift hypothesis
Continents "_____________________" to present positions
Evidence used in support of continental drift hypothesis
Fit of the continents
_______________________evidence
Rock type and structural similarities
________________________ evidence
The Great Debate
Objections to the continental drift _______________________
Inability to provide a mechanism capable of moving continents across the globe
Wegner suggested that continents broke through the ______________________ crust,
much like ice breakers cut through ice
The Great Debate
Continental drift and the scientific method
Wegner’s hypothesis was _________________ in principle, but contained incorrect
details
For any scientific viewpoint to gain wide acceptance, supporting
___________________________ from all realms of science must be found
A few scientists considered Wegner’s ideas ________________ and continued the search
Paleomagnetism
_______________________ minerals in rocks
Show the direction to Earth’s magnetic poles
Provide a means of determining their _______________________ of origin
Revolution of Continental Drift
During the 1950s and 1960s technological strides permitted extensive _______________ of the ocean
floor
Seafloor spreading hypothesis was proposed by ________________ __________ in the early 1960s
_________________________ (evidence of past magnetism recorded in the rocks) was the most
convincing evidence set forth to support the concepts of continental drift and seafloor spreading
Plate Tectonics
Plate tectonics is the theory that the Earth’s lithosphere is divided into _________________ plates that
move around on top of the asthenosphere.
Earth’s major plates
___________________ major lithospheric plates
Plates are in motion and continually changing in shape and _________________
Largest plate is the _____________________ plate
Several plates include an entire continent plus a large area of _____________________
Plate Tectonics
Earth’s major plates
Plates move relative to each other at a very slow but ___________________ rate
– Average about _________ centimeters (2 inches) per year
– Cooler, denser slabs of oceanic lithosphere ____________ into the mantel.
Divergent Plate Boundaries
When 2 tectonic plates ___________________, the boundary is known as a divergent boundary
The 2 plates are moving away from each other.
Most divergent boundaries occur on the ________________. If they occur on land, it forms a valley
called a ____________________
_____________ _______________ _____________- are the result of divergent plate boundaries
Convergent Plate Boundaries
When 2 tectonic plates collide, the boundary is known as a __________________ boundary. (2 plates
come together)
There are ____ different types of convergent plate collisions:
– Continental-Continental
– Continental-Oceanic
– Oceanic-___________________________
When two plates collide, the ________________ of the plates determines which one comes out on top.
Oceanic-Oceanic
The plate that is __________________dense dives under the other plate and returns to the
mantle.
This process is ________________________.
Oceanic-Continental
The oceanic plate dives ______________________the continental plate (called subduction)
Continental-Continental
Subduction does _____________ take place.
The plates crash head-on, folding over one another, squeezing the crust into a
___________________
Transform Boundaries
When 2 tectonic plates slide past one another ___________________, the boundary is a transform
boundary.
San Andreas Fault in ___________________
Transform boundaries cause __________________________ all over the world.
Why do the plates moves?
Three driving forces for plate motion:
1. ____________________: because of ridge push, the oceanic lithosphere slides downhill under
the force of gravity.
2. _______________________: convection causes the oceanic lithosphere to move sideways and
away from the mid-ocean ridge
3. ________________________: oceanic lithosphere is dense and sinks. It pulls the rest of the
tectonic plate with it in a process called slab pull.
Tracking the motion of plates
___________________ is used to track and measure the rate of tectonic plate movement.
Radio signals are beamed from satellites to ground GPS units.
With this information, scientists can _______________ the amount a plate movements within ________
___________