Chapter 7
Plate Tectonics
Answers to Review Questions
1. a) Similarity of coastlines (more precisely the
similarity of the edge of the continental shelves).
Especially South America and Africa.
b) Similarities of the edges of the continental shelves,
similar rock types on each side of oceans match, Fossils
match across the seas, ancient climates are consistent
(glaciers in southern Africa, South America, India and
Australia, tropical climate in Eastern U. S. Europe and
Siberia produced major coal fields). The fresh water
Mesosaurus aren't found globally thereby indicating that
they weren't very mobile, but they are found on adjacent
areas of the reassembled South America and Africa.
c) No mechnisms, that seemed logical with the current
understanding, were proposed to allow the continental plates
to move. Wegener suggested that continents break through
the ocean floor when they moved and that tidal forces were
responsible for this movement.
d) Wegener continued to test his hypothesis by looking for
new testable evidence. He died in Greenland trying to
determine how much Greenland had moved during the last 200
million years.
2. a)
A) ocean floor subducting under a continent
B) ocean subducting under an ocean floor.
C) continent subducting under a continent.
2. b) Ocean floor
2 c) Because they do not contain large amount of water and
they do not subduct as deep. The water serves as a eutectic
which lowers the melting point of rock. Further
more the water relases large amount of gas.
2. d) They are similar in that they both can product
volcanoes. They are different in that in one case the
volcanoes are on a continent and the other the volcanoes
form islands.
3. The Baja peninsula and the area of Los Angeles is
sliding northward and is not beng subducted.
4. a) 3
b) toward. The arrows on the subduction zone.
c) subduction is causing melting and the melted magma is
rsing to the surface forming volcanoes.
d) No subduction underneath and no rifting apart. If
rifting started you could have some volcanoes.
5. Olympus Mons on Mars is the largest volcano tht has been
identified in the solar system. This doesn't tell us
anything about the interior of Mars because we don't have
detailed seimological information about the interior of
Mars. On the surface of Mars there is one region with
alternating magnetic strips which indicates that one area of
Mars may have had something like plate tectonics, but it
isn't widespread.
6. The first one with uniform magnetic stripes has magma
coming up at a constant velocity. The magma coming up in
the 2nd one is slowing down, thus making the magnetic
stripes wider near the crest.
7. Antarctica, Australia and New Zealand were separated
from the other plates by 90 million years ago and have
remained separated until today. North America on the other
hand has been in touch with Asia and South America more
recently, so that causes huge differences in the evolution
of the animals.
8. Eurasia
9. Light magma rises to form hot spots and volcanoes.
Heavy plates sink. When two continents collide with nearly
the same density, huge mountains are produced.
10. a) London and Boston, London and Denver, London and
Mexico City
b) Darwin and Beijing, Delhi and Beijing, Honolulu and
Beijing, Darwin and Honolulu.
c) Boston and Denver, Denver and Mexico City, Boston and
mexico City.