In the mid-1970s, Walter Alvarez, a geologist, was studying Earths

Hello anindame

Maybe this example will help:

we make geological excavations and found 1000 year old layer with presence of crocodile and than next layer 900 years old and still crocodile remains are present and than next layer 800 years old and it has no remains of crocodile. According to "uniformitarian view" we have some problem with this geological data and this absence of croocdile absence doesn't mean that crocodile became extinct in this period.

Passage describes event when dinosaurs suddenly became extinct so this is exactly the case that impossible according to "uniformitarian view" because geological excavations show that dinosaurs suddenly disappear.

Can somebody post the OE for 3rd & 4th question?

Hello lav4
I don't have OE but will write my perception of these question: maybe it helps

3. According to the passage, it can most likely be inferred that iridium

A. can be used by scientists to determine the duration of an event
In passage we have words: "The Alvarezes reasoned that if the clay layer had taken a significant amount of time to deposit, it would contain detectable levels of iridium."
Correct

B. causes mass extinctions in a short period
According to passage asteroid cuased mass extinction

C. gathers excessively in clay deposits
"Iridium, in the form of microscopic grains of cosmic dust, is constantly raining down on the planet."
According to passage iridium gathers on all surface of earth wihout any preferences to clay

D. helps scientists determine the orientation of the magnetic field
At the beginning of the passage we read that Alvarez found that pinkish limestone record changes in magnetic fields but there is no information about relationship between iridium and magnetic field

E. leads to inaccurate conclusions regarding the chronology of an event
In passage we met case of exscessive presence of iridium caused by asteroid but this case doesn't mean that iridium causes inacurate conclusions

===================

4. The Alvarezes concluded that a meteorite was responsible for a mass extinction because

A. dinosaurs were prone to the effects of iridium
Dinosaurs were extinct by asteroid not by iridium

B. it could account for the heightened presence of an element
Alvarez found big presence of iridium and make inference that this fact caused by meteorit and as this site was big he nade inference that this is was huge asteroid that kill dinosauros and other forms of life
Correct

C. cosmic dust in the form of iridium constantly makes its way to the Earth’s surface
It is just fact that doesn't link to the asteroid case

D. the scaglia rossa had a sudden gap in traceable iridium
scaglia rossa didn't have gap in iridium, accroding to passage it just disappear in one moment

E. the scientific community was unable to provide a more valid hypothesis
We don't know about opinions of scientific community about mass extinction

1. It can be inferred from the passage that had the scaglia rossa not exhibited a certain geological property then which of the following would most likely have been true?

B.Scientists would have been unable to determine a shift in the Earth’s magnetic fields.

It had recently been learned that the orientation of the planet’s magnetic field reverses, so that every so often, in effect, south becomes north and vice versa. Alvarez and some colleagues had found that a certain formation of pinkish limestone in Italy, known as the scaglia rossa, recorded these occasional reversals.

One more question regarding this RC.

Which of the following can be most reasonably inferred from the first paragraph?

(A) The forams in the clay were driven to extinction by the impact of a large meteorite
(B) Walter Alvarez was aware of the shortcomings of the uniformitarian view
(C) Iridium is more likely to be found on meteorites than on the surface of the earth
(D) The observation of the absence of forams in the clay layer was in some ways serendipitous
(E) The earth’s magnetic poles were shifted by a catastrophic occurrence


Source: https://magoosh.com/gre/2013/technical- ... lanations/

Explanations:

1. Answer: (A)
We learn from the passage that Alvarez had been using scaglia rosa as part of his studies on Earth’s polarity. Had he not have been, he would not have encountered the foraminifera, which led to his theory on dinosaur extinction. This supports answer (A).
(B) is tempting, but nowhere in the passage does it mention that the only way to learn about shifts in Earth’s magnetic fields is through the use of scaglia rosa.
(C) is similar to (B) in that we do not have enough information. That is nowhere in the passage does it say scientists have no other uses for scaglia rosa.
(D) Had Alvarez not noted the gap in the foraminfera, he would not have arrived at a theory on dinosaur extinction. Thus he would not have had any use for iridium.
(E) Had Alvarez not been studying Earth’s polarity, he would not have studied scaglia rosa and thus not noticed the gap in foraminfera.

2. Answer: (D)
The uniformitarian view is “any apparent extinctions” were a gap in the fossil record. This matches up best with (D).
(A) is wrong because a gap is not the same thing as tiny forams.
(B) is the opposite of what they would think
(C) is incorrect since uniformitarian view does not relate to iridium
(E) is incorrect because the uniformitarian view relates to fossil record

3. Answer: (A)
The passage says, “how long…iridium…answer this question.” This best supports (A).
(B) is wrong because iridium does not cause extinctions. (C) is incorrect because the forma, not the iridium, form in clay deposits. (D) is wrong because iridium does not relate to magnetic fields. (E) is incorrect because the passage suggests that iridium provides accurate, not inaccurate, conclusions about chronology.

4. Answer: (B)
Based on the startling amount of iridium that the Alvarezes found they concluded that only a meteorite could have caused the extinction of the dinosaurs. This matches up best with (B).
(A) is wrong because dinosaurs were not effected by the iridium itself but by the meteorite.
(C), while mentioned in the passage, does not answer the question.
(D) is wrong because the scaglia rosa showed a gap in foraminifera, not iridium.
(E) is incorrect because the passage does not mention the scientific community, nor does it imply that the Alvarez’s explanation was a default one.

Hi everyone,
Took me 11 minutes and got all correct. Took 5 minutes to read, write down paragraph summaries and main point.

P1:WA's study and hypothesis
P2:How iridium led to answer the hypothesis

MP: WA's study, hypothesis and explanation of a phenomenon

1. It can be inferred from the passage that had the scaglia rossa not exhibited a certain geological property then which of the following would most likely have been true?

Pre-thinking: Refer to P1 t answer this question. Here the author reasoning seems to be the following: Scaglia rossa shows the reverse in polarity SO it can be used to analyze the apparent extinction also given the evidence contained into its layers. There is a clear connection between the observation of change in polarity displayed by SR and the usage of SR as evidence.
In conclusion it can be inferred that without being able to show changes in polarity SR would have been useless in evaluating WA'study

A. Walter Alvarez would not have used the distribution of foraminifera in limestone as the basis for a conjecture.
This is in line with our prethinking and hence it is the correct choice

B.Scientists would have been unable to determine a shift in the Earth’s magnetic fields.
Nowhere it is mentioned that SR is the only mean through which scientist would be able to determine such shifts. So incorrect

C.The rocks would not have been of any immediate utility to scientists.
Nowhere mentioned. Hence incorrect

D.Iridium still would have been used to substantiate a hypothesis regarding the extinction of dinosaurs.
Iridium come into play after. Probably if SR had not been able to determine shifts in polarity then it would have not been taken into consideration at all

E.The gap in foraminifera fossil record would have served an immediate purpose.
Same for answer choice D. WA probably would not have taken this evidence into consideration at all.


2. Proponents of the uniformitarian view would most likely argue that

Pre-thinking: Proponents of the uniformitarian view are discussed at the end of the first paragraph so let's refer to that portion of the passage.
Specifically focus on these lines:"uniformitarian view, which held that any apparent extinctions throughout geological time resulted from ‘the incompleteness of the fossil record’ rather than an actual extinction,".
Here what is important is to understand the purpose which is to determine whether an apparent extinction happened or not

A. the clay layer actually contained foram too small for Alvarez to detect.
UV is about determining an apparent extinction through fossil records. This information is irrelevant

B. the absence of foram suggested a mass extinction
This is the trap answer. UV aims at determining an apparent extinction and not an actual one. Hence incorrect

C. iridium could likely be found in the clay layer
This is out of the scope for what regards the UV

D. that the lack of forams in the clay reflected a gap in the fossil record
This is in line with UV, so correct

E.the orientation of the earth’s magnetic field is capable of reversing
Out of scope. Hence incorrect


3. According to the passage, it can most likely be inferred that iridium

Pre-Thinking: Refer to the second paragraph to make all the inferences about Iridium.
"The Alvarezes reasoned that if the clay layer had taken a significant amount of time to deposit, it would contain detectable levels of iridium."
It is clear that the amount of iridium is indicative of the duration of a phenomenon


A. can be used by scientists to determine the duration of an event
In line with Prethinking. Hence correct

B. causes mass extinctions in a short period
nowhere mentioned

C. gathers excessively in clay deposits
Excessively is an extreme word and doesn't describe iridium in general but only for a specific case

D. helps scientists determine the orientation of the magnetic field
Nowhere mentioned

E. leads to inaccurate conclusions regarding the chronology of an event
here inaccurate is wrong. Hence incorrect


4. The Alvarezes concluded that a meteorite was responsible for a mass extinction because

Pre-Thinking:Refer to the last paragraph to find the answer. "The results were startling: far too much iridium had shown up." Here you can see that the huge amount of Iridium found in the limestone led to the conclusion that a meteorite was responsible for mass extinction.

A. dinosaurs were prone to the effects of iridium
Nowhere mentioned and cannot be inferred. Hence incorrect

B. it could account for the heightened presence of an element
Yes. The element is the iridium which was found in great quantities. Hence correct.

C. cosmic dust in the form of iridium constantly makes its way to the Earth’s surface
out of context. This was mentioned to show why iridium was present in the limestone. Hence incorrect

D. the scaglia rossa had a sudden gap in traceable iridium
No gap but great concentration of iridium. Hence incorrect

E. the scientific community was unable to provide a more valid hypothesis
This was never mentioned and cannot be inferred. Hence incorrect

For Q#3 -
Isn't the word "event" in answer choice A too broad? I selected answer choice C because "A" kind of sounded to me that it can determine the duration of any event.
Can any expert please explain?

3. According to the passage, it can most likely be inferred that iridium

A. can be used by scientists to determine the duration of an event

B. causes mass extinctions in a short period

C. gathers excessively in clay deposits

D. helps scientists determine the orientation of the magnetic field

E. leads to inaccurate conclusions regarding the chronology of an event

Hi there,
Answer choice A may not be specific but it conveys the right meaning. Through iridium we can understand the duration of the extinction.
On the other hand choice C has nothing to do with Iridium and cannot be the right choice.
Hope this helps!

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