The Earth comprises three principal layers : the dense, iron-rich core, the
mantle
made of silicate rocks that are semimolten at depth, and the thin,
solid-surface crust.
There are two kinds of crust, a lower and denser oceanic crust and
an upper, lighter
Line continental crust found over only about 40 percent of the Earth's
surface. The rocks
(5) of the crust are of very different ages. Some continental rocks
are over 3,000 million
years old, while those of the ocean floor are less then 200 million
years old. The crusts
and the top, solid part of the mantle, totaling about 70 to 100
kilometers in thickness,
at present appear to consist of about 15 rigid plates, 7 of which
are very large. These
plates move over the semimolten lower mantle to produce all of the
major topographical
(10) features of the Earth. Active zones where intense deformation
occurs are confined to
the narrow, interconnecting boundaries of contact of the plates.
There are three main types of
zones of contact : spreading contacts where plates move
apart, converting contacts where plates move towards each other,
and transform
contacts where plates slide past each other. New oceanic crust is
formed along one or
(15) more margins of each plate by material issuing from deeper layers
of the Earth's crust,
for example, by volcanic eruptions of lava at midocean ridges. If
at such a spreading
contact the two plates support continents, a rift is formed that
will gradually widen and
become flooded by the sea. The Atlantic Ocean formed like this as
the American and
Afro-European plates moved in opposite directions. At the same time
at margins of
(20) converging plates, the oceanic crust is being reabsorbed by being
subducted into the
mantle and remelted beneath the ocean trenches. When two plates
carrying continents
collide, the continental blocks, too light to be drawn down,
continue to float and
therefore buckle to form a mountain chain along the length of the
margin of the plates.
Questions
21. The word "comprises" in line 1 is closest in meaning
to
(A) adapts to
(B) benefits from
(C) consists of
(D) focuses on
22. According to the passage, on approximately what percent of the
Earth's surface is the
continental crust found?
(A) 15
(B) 40
(C) 70
(D) 100
23. The word "which" in line 8 refers to
(A) crusts
(B) kilometers
(C) plates
(D) continents
24. The word "intense" in line 10 is closest in meaning
to
(A) surface
(B) sudden
(C) rare
(D) extreme
25. What does the second paragraph of the passage mainly discuss?
(A) The major mountain chains
of the Earth
(B) Processes that create the
Earth's surface features
(C) The composition of the
ocean floors
(D) The rates at which
continents move
26. Which of the following drawings best represents a transform
contact (line 13-14)?
27. The word "margins" in line 15 is closest in meaning
to
(A) edges
(B) peaks
(C) interiors
(D) distances
28. The word "support" in line 17 is closest in meaning
to
(A) separate
(B) create
(C) reduce
(D) hold
29. According to the passage, mountain ranges are formed then
(A) the crust is remelted
(B) two plates separate
(C) a rift is flooded
(D) continental plate collide
30. Where in the passage does the author describe how oceans are
formed?
(A) Lines 3-4
(B) Lines 6-8
(C) Lines 16-18
(D) Lines 19-21
Please tally your answer with the below provided answers and
then comment here how much you got!
Answers
21. C 22. B 23. C 24. D 25.
B 26. D 27. A 28. D 29. D 30. C
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