Review of Plate Tectonics
Name ________________________
Date ____________
1. Wegener’s hypothesis was that the continents had all once been ______________and had drifted apart.
2. Wegener named the supercontinent ___________________________ .
3. Wegener’s theory was called ______________________________________.
4. Use one sentence to explain the following evidences for his theory:
a. Evidence from landforms.
b. Evidence from fossils
c. Evidence from climate
5. Scientists rejected Wegener’s theory because he could not explain __________________
6. Today we have new evidence that explains what is causing the “Contintental Drift”. We now call the
theory that explains this ______________________________.
7. At the mid-ocean ridge, molten material _______________ from the mantle and erupts, then spreads
out, pushing _________ rock to both sides of the ridge. This process is called
____________________________.
8. Some evidence for plate tectonics are the following:
a. We sent down a submersible to take pictures on the sea floor and found that in the central valley
of the mid-ocean ridge, lava was coming out of an opening crack called a ________. The lava
was shaped like pillows or toothpaste squeezed from a tube. This “pillow lava” was everywhere,
showing that the molten material had erupted again and again from cracks along the central
valley of the ____________________________.
b. Scientists discovered that rock that makes up the ocean floor lies in a pattern of magnetized
stripes and that these stripes hold a record of reversals in the Earth’s
______________________________. The pattern of stripes which is the same on both sides of
the mid-ocean ridge showed that the sea floor has spread from the
________________________________.
c. Evidence for sea floor spreading came from rock samples from taking
______________________of the ocean floor by the ship called
_____________________________________. Samples from the sea floor were dated and the
youngest rocks were always at the ______________ of the mid-ocean ridges.
9. Mid-ocean ridges where sea floor spreading is taking place is an example of a
___________________________ plate boundary. In the middle of the mid-ocean ridge is a
___________ valley. Iceland is an example of a country that is located on an above-sea level portion of
the ______________________________.
10. Another example of a _____________ plate boundary can found in the middle of a continent, is in East
Africa and is called the Great Rift Valley. Along this crack, the rift may someday split the eastern part
of Africa away from the rest of the continent. As the rift valley widens, its floor gets__________.
Eventually the sea will fill in the widening gap.
11. The place where two plates come together is called a ____________________ boundary.
12. When two plates collide, the ________________ of the plates determines which one comes out on top.
Oceanic crust is ________________ dense than continental crust. The types of _______________
boundaries are oceanic/oceanic, oceanic/continental, and continental/ continental.
13. When an oceanic plate edge collides with a continental boundary, the more dense _________________
dives under the less dense _________________________. This process is known as _____________
Where this takes place, cracks in the lithosphere, causes lava to rise up and erupt to form ___________
Some of the deepest holes in the ground called _________ are found at these types of plate boundaries.
14. An example of a subduction zone can be found where the __________________ Ocean meets continents.
A ring of volcanoes at this location is called the __________________________________________.
15. When two plates carrying continents collide, _____________________ do not take place. Both
continental plates are mostly __________ in density so neither plate is ______________ enough to sink
into the mantle. Instead the plates crash head-on and squeeze the crust into mighty
___________________________. An example of this is where India on the Indoaustralian Plate
crashed into Asia and is still forming the __________________________ mountains.
16. The Appalachian Mountains on the ____________ coast of the United States formed along time ago in
the formation of _____________________. At one time they were mighty mountains like the
Himalayas, but over many years were ______________________ to their present day height.
17. Another type of plate boundary occurs where two plates are side-swiping each other. At this type of site
the faults get locked together with friction and store __________ stress over a long time. When the
fault finally breaks apart, the sudden motion causes earthquakes. An example of this type of plate
boundary can be found in the state of _________________ at the ____________________ fault.
18. The process that powers Plate tectonics are large circular currents called _______________. These
currents take place in the __________________ layer of the earth. _________________ boundaries
occur at places where there is an upcurrent. While ________________boundaries occur where there is
a down current.
19. Additionally, there are places, such as Hawaii, with volcanoes that are not located on a place boundary.
These are called _________________________. Hawaii is a chain of volcanoes because…
____________________________________________________________________________________
20. The type of magma that is viscous is formed from ____________________ crust. At
_______________________ boundaries this type of magma causes ______________ to get trapped
underground resulting in __________________________ volcanoes.
21. ______________________ crust found at diverging boundaries and at hot spots does not produce
explosive volcanoes because __________________________________________________________
22. A map of earthquakes around the earth was done and it was shown that there are a lot of earthquakes at
30 degrees North latitude by 75 degrees East longitude. What is occurring there that is causing this?