Samantha_Hernandez_Chapter_2
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Dec 6, 2023
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Chapter 2 Plate Tectonics Assignment
1. Explain why the discovery of the fossil remains of Mesosaurus in both South America and
Africa, but nowhere else, supports the continental drift hypothesis.
Mesosaurus couldn't have crossed an ocean between the two continents which suggest that the
continents were connected at one time.
2. Compare and contrast the lithosphere and the asthenosphere.
The lithosphere and the asthenosphere are both parts of a mantle and parts of the interior
earth. The lithosphere is the hard and rigid uppermost part of the mantle and crust. The
asthenosphere is the soft layer in the lower part of the mantle.
3. List the three types of plate boundaries, and describe the relative motion at each of them.
Divergent boundaries -- where new crust is generated as the plates pull away from each
other.
Convergent boundaries
-- where crust is des`troyed as one plate dives under another.
Transform boundaries -- where crust is neither produced nor destroyed as the plates slide
horizontally past each other.
4. Briefly describe the process of continental rifting. Where is it occurring today?
As the plates pull apart the crust, the broken crustal fragments drop, generating an elongated
depression called a continental rift. An example today is the
East African Rift
.
5. Compare a continental volcanic arc and a volcanic island arc.
An island volcanic arc forms in an ocean basin via ocean-ocean subduction. A continental
volcanic arc forms along the margin of a continent where oceanic crust sub ducts beneath
continental crust
.
6. Why does oceanic lithosphere subduct while continental lithosphere does not?
The plate made of oceanic lithosphere will sub duct because it is denser than the plate made of
continental lithosphere.
7. Briefly describe how mountain systems such as the Himalayas form.
Mountains form
where two continental plates collide
. Since both plates have a similar thickness
and weight, neither one will sink under the other.
8. What is the age of the oldest sediments recovered by deep-ocean drilling? How do the ages
of these sediments compare to the ages of the oldest continental rocks? Why are there no “old”
oceanic rocks?
Oldest age of sediment recovered is
180 million years old
. Most continental crust exceeds
several hundred million years and some have been located that exceed 4 billion years. There are
no old oceanic rocks because the oceanic crust is eventually destroyed in subduction zones
.
Even thought it has been forming on Earth for over 4 billion years, all of the sea floor older than
about 200 million years has been recycled by plate tectonics.
9. Briefly describe how hot-spot tracks can be used to determine the rate of plate motion.
By using the age of the eruptions from hot spots and the direction of the chain of events
, one
can identify a specific rate and direction of movement of a plate over the time the hot spot was
active.
10. Describe slab pull and ridge push. Which of these forces appears to contribute more to plate
motion?
Slab Pull. It occurs because cold slabs of oceanic lithosphere are denser than the underlying
warm asthenosphere and hence "sink like a rock" Ridge push results from elevated position of
the oceanic ridge, which causes slabs of lithosphere to slide down the ridge.
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