Reading Comprehension

Until the 1980s, most scientists believed that
noncatastrophic geological processes caused the
extinction of dinosaurs that occurred approximately
66 million years ago, at the end of the Cretaceous
(5)period. Geologists argued that a dramatic drop in
sea level coincided with the extinction of the
dinosaurs and could have caused the climatic
changes that resulted in this extinction as well as
the extinction of many ocean species.

(10) This view was seriously challenged in the 1980s
by the discovery of large amounts of iridium in a
layer of clay deposited at the end of the Cretaceous
period. Because iridium is extremely rare in rocks
on the Earth's surface but common in meteorites,
(15) researchers theorized that it was the impact of a
large meteorite that dramatically changed the
Earth's climate and thus triggered the extinction of
the dinosaurs.

Currently available evidence, however, offers
(20) more support for a new theory, the volcaniceruption
theory. A vast eruption of lava in India
coincided with the extinctions that occurred at the
end of the Cretaceous period, and the release of
carbon dioxide from this episode of volcanism could
(25) have caused the climatic change responsible for the
demise of the dinosaurs. Such outpourings of lava
are caused by instability in the lowest layer of the
Earth's mantle, located just above the Earth's core.
As the rock that constitutes this layer is heated by
(30)the Earth's core, it becomes less dense and portions
of it eventually escape upward as blobs of molten
rock, called "diapirs," that can, under certain
circumstances, erupt violently through the Earth's
crust.

(35) Moreover, the volcanic-eruption theory, like the
impact theory, accounts for the presence of iridium
in sedimentary deposits; it also explains matters
that the meteorite-impact theory does not.
Although iridium is extremely rare on the Earth's
(40) surface, the lower regions of the Earth's mantle
have roughly the same composition as meteorites
and contain large amounts of iridium, which in the
case of a diapir eruption would probably be emitted
as iridium hexafluoride, a gas that would disperse
(45) more uniformly in the atmosphere than the
iridium-containing matter thrown out from a
meteorite impact. In addition, the volcanic-eruption
theory may explain why the end of the Cretaceous
period was marked by a gradual change in sea level.
(50) Fossil records indicate that for several hundred
thousand years prior to the relatively sudden
disappearance of the dinosaurs, the level of the sea
gradually fell, causing many marine organisms to
die out. This change in sea level might well have
(55)been the result of a distortion in the Earth's surface
that resulted from the movement of diapirs upward
toward the Earth's crust, and the more cataclysmic
extinction of the dinosaurs could have resulted from
the explosive volcanism that occurred as material
(60) from the diapirs erupted onto the Earth's surface.



1. The passage suggests that during the 1980s researchers found meteorite impact a convincing explanation for the extinction of dinosaurs, in part because
(A) earlier theories had failed to account for the gradual extinction of many ocean species at the end of the Cretaceous period
(B) geologists had, up until that time, underestimated the amount of carbon dioxide that would be released during an episode of explosive volcanism
(C) a meteorite could have served as a source of the iridium found in a layer of clay deposited at the end of the Cretaceous period
(D) no theory relying on purely geological processes had, up until that time, explained the cause of the precipitous drop in sea level that occurred at the end of the Cretaceous period
(E) the impact of a large meteorite could have resulted in the release of enough carbon dioxide to cause global climatic change



2. According to the passage, the lower regions of the Earth's mantle are characterized by
(A) a composition similar to that of meteorites
(B) the absence of elements found in rocks on the Earth's crust
(C) a greater stability than that of the upper regions
(D) the presence of large amounts of carbon dioxide
(E) a uniformly lower density than that of the upper regions


3. It can be inferred from the passage that which one of the following was true of the lava that erupted in India at the end of the Cretaceous period?
(A) It contained less carbon dioxide than did the meteorites that were striking the Earth's surface during that period.
(B) It was more dense than the molten rock, located just above the Earth's core.
(C) It released enough iridium hexafluoride into the atmosphere to change the Earth's climate dramatically.
(D) It was richer in iridium than rocks usually found on the Earth's surface.
(E) It was richer in iridium than were the meteorites that were striking the Earth's surface during that period.


4. In the passage, the author is primarily concerned with doing which one of the following?
(A) describing three theories and explaining why the latest of these appears to be the best of the three
(B) attacking the assumptions inherent in theories that until the 1980s had been largely accepted by geologists
(C) outlining the inadequacies of three different explanations of the same phenomenon
(D) providing concrete examples in support of the more general assertion that theories must often be revised in light of new evidence
(E) citing evidence that appears to confirm the skepticism of geologists regarding a view held prior to the 1980s


5. The author implies that if the theory described in the third paragraph is true, which one of the following would have been true of iridium in the atmosphere at the end of the Cretaceous period?
(A) Its level of concentration in the Earth's atmosphere would have been high due to a slow but steady increase in the atmospheric iridium that began in the early Cretaceous period.
(B) Its concentration in the Earth's atmosphere would have increased due to the dramatic decrease in sea level that occurred during the Cretaceous period.
(C) It would have been directly responsible for the extinction of many ocean species.
(D) It would have been more uniformly dispersed than iridium whose source had been the impact of a meteorite on the Earth's surface.
(E) It would have been more uniformly dispersed than indium released into the atmosphere as a result of normal geological processes that occur on Earth.


6. The passage supports which one of the following claims about the volcanic-eruption theory?
(A) It does not rely on assumptions concerning the temperature of molten rock at the lowest pan of the Earth's mantle.
(B) It may explain what caused the gradual fall in sea level that occurred for hundreds of thousands of years prior to the more sudden disappearance of the dinosaurs.
(C) It bases its explanation on the occurrence of periods of increased volcanic activity similar to those shown to have caused earlier mass extinctions.
(D) It may explain the relative scarcity of iridium in rocks on the Earth's surface compared to its abundance in meteorites.
(E) It accounts for the relatively uneven distribution of iridium in the layer of clay deposited at the end of the Cretaceous period.


7. Which one of the following, if true, would cast the most doubt on the theory described in the last paragraph of the passage?
(A) Fragments of meteorites that have struck the Earth are examined and found to have only minuscule amounts of iridium hexafluoride trapped inside of them.
(B) Most diapir eruptions in the geological history of the Earth have been similar in size to the one that occurred in India at the end of the Cretaceous period and have not been succeeded by periods of climatic change.
(C) There have been several periods in the geological history of the Earth, before and after the Cretaceous period, during which large numbers of marine species have perished.
(D) The frequency with which meteorites struck the Earth was higher at the end of the Cretaceous period than at the beginning of the period.
(E) Marine species tend to be much more vulnerable to extinction when exposed to a dramatic and relatively sudden change in sea level than when they are exposed to a gradual change in sea level similar to the one that preceded the extinction of the dinosaurs.

C
A
D
A
D
B
B

pretty easy RC actually.

1 e 2 a
3 e
4 a
5e
6 b
7 b

1) C
2) A
3) C
4) A
5) D
6) B
7) B

1 C
2 A
3 C
4 A
5 D
6 B
7 B D

17MINUTE


OA please?

C
A
C
A
D
B
B

C
e
C
A
D
B
B

15 minutes 30 seconds

Topic and Scope: Dinosaur extinction; specifically, various different contemporary
theories for dinosaurs' disappearance.
Purpose and Main Idea: The author spends most of the time explaining and touting the
newest of three theories (the "volcanic-eruption theory") as to why the dinosaurs died out.
Two earlier theories are described as well, but the author seems to have the most
confidence in this new one.
Paragraph Structure: Each of the first three paragraphs is devoted to a thumbnail
description of a theory: the "climatic theory" (¶1) that held sway until the 1980s; the
"meteorite-impact theory" (¶2) popular in the '80s; and the "volcanic-eruption theory" (¶s
3-4), which is supported by newly-discovered evidence in India. The introductory
keyword "Moreover" leads us to expect more information about the new theory, and that's
just what we get: We learn that the evidence for the other two theories (the change in sea
level and the iridium deposits) supports, or at least is consistent with, the eruption theory
as well.


1. (C)
This choice is a nice paraphrase of information in ¶2, which describes the nuts and bolts of
the "meteorite-impact theory."
(A) Au contraire. Lines 5-9 demonstrate that the "climactic theory"-a theory that preceded
the "meteorite-impact theory"-could account for the extinction of ocean species at the
end of the Cretaceous era.
(B) refers to the details of the "volcanic-eruption theory," a new theory intended to take the
place of the older "meteorite-impact theory" of the 1980s.
(D) Au contraire aussi. ¶1 says that researchers initially thought that the drop in sea level
thought to be behind the mass extinction episode at the end of the Cretaceous era was the
result of "noncatastrophic geological processes."
(E) mistakenly attributes an element of the "volcanic-eruption theory" to the "meteoriteimpact
theory."
"¢ When a passage discusses several different theories or scenarios, be sure that you're
clear about the details of each-the questions will certainly test to see that you are.


2. (A)

The depths of the Earth's mantle are described in two places, line 28 and line 40, and we
hope you kept reading past the first reference because the right answer is yielded by the
second. Lines 40-41 are choice (A) almost word-for-word.
(B) Only the element iridium is described here, and in fact that's an element that is present
in the mantle but rare on the Earth's surface. (B) gets it all cockeyed.
(C) According to lines 27-28, the mantle is rather unstable, and we get no information as to
whether things are more stable closer to the surface.
(D) The only reference to CO2 comes in line 24, before the mantle is even mentioned, and
all we're told is that it's released with lava. Yes, the lava eruption is triggered by mantle
instability, but that's a long way from what (D) is saying.
(E) As with (C), we're given no comparison between the mantle and the upper regions.
And, anyhow, the mantle (when heated by the core) becomes less dense in places, not
"uniformly" so.

3. (D)

Lines 39-43 say that the Earth's mantle is rich in iridium, while its surface doesn't have
much of the stuff. Hence, we can infer that Cretaceous era lava (lava is just heated rock
from the Earth's interior) "was richer in iridium" than surface rock.
(A) is beyond the scope of the passage, which never compares Cretaceous era lava with
meteorites in terms of their respective carbon dioxide content.
(B) Au contraire. Lines 29-32 indicate that lava is no more dense than-and may well be less
dense than-the molten rock just above the Earth's core.
(C) According to the "volcanic-eruption theory," the Earth's climate was changed by
massive volcanic eruptions, not by the release of iridium hexaflouride, which was simply a
byproduct of those eruptions.
(E) The "volcanic-eruption theory" states that Cretaceous era lava distributed iridium
more evenly on the Earth's surface than meteorite impacts could have; it doesn't, however,
claim that the lava was richer in iridium than meteorites

4. (A)

What could be more of a slam dunk? If you pre-phrased an answer after reading the
passage but before reading the choices, it's possible that you came up with (A) almost
word-for-word.
(B), (C) "Attacking"? "Inadequacies"? The author isn't critical of any of the theories. She's
just reporting on which theories have held sway when. And (B)'s implication that more
than one theory was popular before the 1980s is just inaccurate, as line 10 makes clear.
(D) implies that the topic and scope of the passage focus on general principles of scientific
inquiry, and the relationship between evidence and theories. But no "general assertion" is
made; this passage is, as noted above, a straightforward examination of dinosaur extinction
theories, based largely on chronology.
(E) is a mess. No "skepticism" is confirmed, and the "view held prior to the 1980s" is but
one of the three theories explained, not the highlight of the passage.


5. (D)

This choice is an excellent paraphrase of the information contained in lines 42-47.
(A) is beyond the scope of the passage, which only discusses possible developments at the
end of the Cretaceous era.
(B) According to the "volcanic-eruption theory," the increase in atmospheric iridium and
the drop in sea level were both caused by volcanic activity; there was no direct connection
between the drop in sea level and the rise in atmospheric iridium levels.
(C) Again, the extinction of ocean species at the end of the Cretaceous era, according to the
volcanic theory, was due to volcanic activity, not to rising levels of iridium in the
atmosphere.
(E) The "volcanic-eruption theory" never claims that iridium is released into the
atmosphere through "normal geological processes." This last phrase is associated with the
"climactic theory" discussed in ¶1.

6. (B)

Lines 54-57 say that, according to the "volcanic-eruption theory," the gradual fall in sea
level was the result of the upward movement of diapirs toward the Earth's surface.
(A) Lines 26-34 demonstrate that this theory makes assumptions about the temperature of
molten rock just above the Earth's core.
(C) is beyond the scope of the text, which doesn't discuss episodes of mass extinction
before the one at the end of the Cretaceous era.
(D) While the "volcanic-eruption theory" explains the distribution of iridium on the
Earth's surface, it doesn't try to explain either the relative scarcity of this element on the
Earth's surface or its relative abundance in meteorites.
(E) According to the "volcanic-eruption theory," iridium should be distributed relatively
evenly in this layer of clay.

7. (B)

The "volcanic-eruption theory" claims that volcanic activity caused the climactic changes
that resulted in the mass extinction that occurred at the end of the Cretaceous era. If similar
volcanic activity had occurred at other times, but had not resulted in climactic changes,
then we'd have to think twice about whether this theory is in fact on the right track.
(A) The "volcanic-eruption theory" claims that iridium hexaflouride comes from the
Earth's interior. Hence, the theory wouldn't be called into question if meteorites were
found to have only minor quantities of the stuff. If anything, this evidence would tend to
strengthen the theory.
(C) The existence of other episodes of mass extinction would have no bearing on the
"volcanic-eruption theory," which (so far as we know, anyway) concerns only the mass
extinction at the end of the Cretaceous era.
(D) The "volcanic-eruption theory" doesn't deny that meteorites hit the Earth at the end of
the Cretaceous era; it simply claims that, however frequent these impacts may have been,
they can't account for the physical evidence associated with the mass extinction at the end
of this era.
(E) If marine species are in fact more vulnerable to sudden changes in sea level than to
gradual changes, this fact would in no way undermine the notion that they could've
succumbed to a gradual change at the end of the Cretaceous era, as the "volcanic-eruption
theory" suggests