In 1994, a team of scientists led by David McKay began studying the me

Refer to the following sentence: "McKay’s team has demonstrated that the concentration of PAHs increases as one looks deeper into ALH84001, contrary to what one would expect from terrestrial contamination." The word "contrary" suggests that we would expect the opposite to be true if the PAHs were the result of terrestrial contamination. In other words, if the PAHs were the result of terrestrial contamination, the concentration of PAHs would likely DECREASE as one looks deeper into (i.e. moves towards the center of) the meteorite. This matches choice (E).

This makes intuitive sense--imagine a huge ball of rock that lands on Earth with no PAHs. If the rock then becomes contaminated with PAHs while sitting on Earth for thousands of years, we would expect the contamination to affect the surface and then perhaps gradually seep in towards the center.

As for choice (B), if a meteorite contains PAHs that were a result of terrestrial contamination, then we would know nothing of its origin. Maybe it came from Mars, maybe it came from anywhere else in the galaxy. All we would know is that those terrestrial PAHs should not be viewed as evidence of LIFE wherever the meteorite came from. For example, if scientists could PROVE that the PAHs in ALH84001 were a result of terrestrial contamination, this would not change the generally accepted fact that ALH84001 came from Mars. It would simply mean that the PAHs are not evidence of life on Mars.


The last sentence of the first paragraph is: "When microbes die, their organic material often decays into PAHs." (a microbe is a microorganism).

So if you have microorganisms (i.e. bacteria) that die and decay, you'll often be left with PAHs. The presence of PAHs could be viewed as evidence that life may have existed. Thus, this sentence identifies a possible organic source (e.g. microbes) for the PAHs found in the ALH84001, as stated in choice (A).

As for choice (B), the sentence does not describe a FEATURE of PAHs or how PAHs differ from other types of organic molecules.

I hope that helps!
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Passage breakdown

In the first paragraph (P1), the author presents a claim made by a team of scientists

• McKay's team claims that a certain meteorite shows that life once existed on Mars.
• They believe that the presence of organic matter in the meteorite supports this claim.

In the second paragraph, the author presents two arguments against McKay's conclusion, and McKay's response to those arguments.

• Skeptics worry about terrestrial contamination, and also assert that the matter in the meteorite might not have come from organic life.
• The author presents McKay's response to these arguments.

For more on this process, check out this article and our live RC videos.

Explanations for individual questions

• Question 1
• Question 3
• Question 4
• Question 5

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P1 - a rock found - Martian - organic + PAH
P2 - 2 opposition argument of P1 - evidence to break them.
main point - a theory is given and a debate an a topic is going on.

1. The primary purpose of the passage is to:

(A) describe new ways of studying the possibility that life once existed on Mars - no
(B) revise a theory regarding the existence of life on Mars in light of new evidence - no; this one is little part of the passage.
(C) reconcile conflicting viewpoints regarding the possibility that life once existed on Mars - in part it is true, but those viewpoints were broken later that is not covered.
(D) evaluate a recently proposed argument concerning the origin of ALH84001 - very weak; also not evaluate of this argument.
(E) describe a controversy concerning the significance of evidence from ALH84001 - best of the lot.
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2. The passage asserts which of the following about the claim that ALH84001 originated on Mars?
multiple claims made in both p1 and p2.

(A) It was initially proposed by the McKay team of scientists. - no; it was known prior to that.
(B) It is not a matter of widespread scientific dispute. - yes; all accepted that it was from mars. no dispute there.
(C) It has been questioned by some skeptics of the McKay team’s work. - no one did that.
(D) It has been undermined by recent work on PAHs. - no.
(E) It is incompatible with the fact that ALH84001 has been on Earth for 13,000 years. - no.

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3. The passage suggests that the fact that ALH84001 has been on Earth for 13,000 years has been used by some scientists to support which of the following claims about ALH84001?
PT - That this rock must have contaminated by now.

(A) ALH84001 may not have originated on Mars. - no
(B) ALH84001 contains PAHs that are the result of nonbiological processes. - no
(C) ALH84001 may not have contained PAHs when it landed on Earth. - yes; should be best of the lot.
(D) The organic molecules found in ALH84001 are not PAHs. - no
(E) The organic molecules found in ALH84001 could not be the result of terrestrial contamination. - yes; but 13000 yes has nothing to do with this fact.

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4. The passage suggests that if a meteorite contained PAHs that were the result of terrestrial contamination, then one would expect which of the following to be true?
PT - from top to inside, contamination should decrease.

(E) The PAHs contained in the meteorite would be concentrated toward the meteorite’s surface. - yes

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5. Which of the following best describes the function of the last sentence of the first paragraph?
last sentence - The organic molecules found in ALH84001 are poly cyclic aromatic hydrocarbons, or PAHs. When microbes die, their organic material often decays into PAHs.

(A) It identifies a possible organic source for the PAHs found in ALH84001. - yes

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6. The passage suggests that McKay’s team would agree with which of the following regarding the PAHs produced by non organic processes?
Yet McKay’s team notes that the particular combination of PAHs in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating from non biological processes.

(D) These PAHs are likely to be found in combinations that distinguish them from the PAHs produced by organic processes. - yes
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OE #1 : Only option E correctly states that a controversy is described

OE #2 :The passage states scientist generally agree hence it is not a disputed matter.

OE #3 : This is a 'Supporting Ideas' questions. Lines 4-5 in second paragraph point to C

OE #4 : Answering 'Application' question involves applying information contained in the passage to a situation that is not described in the passage. The passage also indicates that if terrestrial contamination occurred with ALH84001, then, contrary to the findings of McKay’s team that showed PAH concentration increases as one looks deeper into ALH84001 (lines 21–22), the PAHs would be expected to be concentrated more toward the outer parts, or surface, of ALH84001

OE #5 : 'Evaluation' questions require understanding how a part of the passage functions within the passage as a whole. The final sentence of the first paragraph indicates that one source of PAHs is the decay of dead microbes.

OE #6: It is an inference question McKay’s team notes in { lines 29–34 }that the PAH combinations produced by organic processes can be distinguished from those produced by non organic processes

Hi Valerun,
Pls. rephrase and post your entire question so that someone can answer it correctly.

From what I gather, you got the 5th RC question wrong and would like to know which sentence points to the correct option ( A)
As mentioned in the OE --It is the last sentence of the first paragraph "When microbes die, their organic material often decays into PAHs."
Hope this answers your question



Hi Prasannajeet,
Have you read the given OE for 2,3,6?
Even after reading the OE if you have any specific doubts then do post them.

Time depends on your technique (skimming and re-reading for details OR reading once with details)
for short RC passage (only reading) on an average should take anywhere from 1-1.30 mins
Thereafter answering question around a 45 secs to 1.15 min per question (this will vary depending the question length,type,and difficulty)

Please go through the the link for RC strategy
all-rc-strategy-official-q-by-experts-legendary-club-members-145027.html

HTH

2: The passage says: "ALH84001, which scientists generally agree originated on Mars, contained compelling evidence that life once existed on Mars".

So, it looks the claim that ALH84001 originated on Mars, is not a matter of widespread scientific dispute. So, B is correct.

3: ALH84001 has been on Earth for 13,000 years, suggesting to some scientists that its PAHs might have resulted from terrestrial contamination.

Hence, C is correct because it says that ALH84001 may not have contained PAHs when it landed on Earth. Perhaps B comes close, but it says that ALH84001 contains PAHs that "are" the result of nonbiological processes. So, the presence of the definitive "are" tilts the balance against B.

6: Last sentence of the passage says: Particular combination of PAHs in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating from non biological processes. Hence, D seems to be correct, because it is stating the same.

Hi pikolo2510,

Let me try to answer your question. I am pasting the portion of the passage which is relevant to answer this question.

The skeptics’ strongest argument, however, is that processes unrelated to organic life can easily produce all the evidence found by McKay’s team, including PAHs. For example, star formation produces PAHs. Moreover, PAHs frequently appear in other meteorites, and no one attributes their presence to life processes. Yet McKay’s team notes that the particular combination of PAHs in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating from non biological processes.

Now coming to the Q:6,
6. The passage suggests that McKay’s team would agree with which of the following regarding the PAHs produced by non organic processes?

Although non organic / non biological processes can produce PAHs the combination PAHs originating from non biological processes is different, as McKay’s team notes that the particular combination of PAHs in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating from non biological processes.


This is what that option D says. D. These PAHs (the PAHs produced by non organic processes) are likely to be found in combinations that distinguish them from the PAHs produced by organic processes.

Hope it clears your doubts. Let me know if you have any questions.

Thanks.
-Varun

Hello GMATNinja

i Refered to the following sentence: "McKa y’s team has demonstrated that the concentration of PAHs increases as one looks deeper into ALH84001, contrary to what one would expect from terrestrial contamination." and chose D

if concentration increases than it is from MARS, if contrary ---> if concentration decreasses, that means tha meteorite would contain fewer PAHs than most other meteorites contain ? no i was sure about my answer

First of all, we do not know that it is from Mars just because concentration of PAHs increases with depth. If the PAHs were the result of terrestrial contamination, the concentration of PAHs would likely DECREASE as one looks deeper into (i.e. moves towards the center of) the meteorite. However, just because this is NOT the case does not necessarily mean the meteorite is from Mars.

Also, how the concentration varies with depth does not tell us anything about the TOTAL amount of PAHs in the meteorite. For example, imagine one meteorite with PAHs from terrestrial contamination and, thus, a higher concentration of PAHs toward the surface. Another meteorite could have PAHs from organic molecules and a higher concentration towards the center. However, the TOTAL number of PAHs in the second meteorite could be less than, equal to, or greater than the total number of PAHs in the first meteorite.

Again, how the concentration varies with depth doesn't tell us anything about the TOTAL number of PAHs. The first meteorite (terrestrial contamination) might have MORE total PAHs than the second (PAHs formed from organic life). Based on the information in the passage, we have no idea whether (D) would be true.

I hope that helps!
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No problem, bondtradercu.


We need to confirm why scientists are referencing the amount of time that ALH84001 has been on Earth. Let's start with a close look at this part of the passage:

"...ALH84001 has been on Earth for 13,000 years, suggesting to some scientists that its PAHs might have resulted from terrestrial contamination.

• terrestrial means "from Earth." In the passage itself, we've read that "Organic molecules...form the basis for terrestrial life."
• If the PAHs ALH84001 resulted from terrestrial contamination, then these PAHs might not have been present in ALH84001 before it landed on Earth.

Consequently, the correct choice will be a claim suggesting that PAHs were not present in the meteorite until after it landed on Earth. This is directly in line with why the author brings up the number of years ALH84001 has been on Earth and what that fact implies to some scientists.


This choice is almost the opposite of what we're looking for. If ALHF84001 contains PAHs that result from non biological processes (like star formation), then it would follow that these PAHs were present in ALHF84001 before it landed on Earth. That's why we eliminate (B).


This choice is much more in line with what we've read, which is why it's the best answer choice.
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AjiteshArun
I have doubt in Q1 though I marked it correct
I didn't understand the meaning of option C
I googled the meaning of reconcile it is to make friendly relation but what actually the sentence is trying to mean can you please brief ?

Reconcile has a different meaning here. It means "to show that two seemingly contradictory things are somehow compatible".

Here is a more accurate look at the meaning of reconcile (the first meaning on that page).

"Reconcile conflicting viewpoints regarding X" means "show how conflicting viewpoints about X could be compatible with each other (even though they are "conflicting")".
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GMATNinja,

In Q2, why we are ignoring the fact that in whole passage we are discussing whether meteorite ALH84001 was originated on mars or not ?

For this several scientist argued PAH might be originated on earth.It was matter of dispute as mentioned in option B.

If we are saying "B" is wrong here, then the primary purpose of this passage as mentioned in Q1 can't be option E "describe a controversy concerning the significance of evidence from ALH84001".

Kindly clarify.

Hi Harsh

I feel you have mixed up two different aspects of the asteroids.

i) The fact that it originated on Mars is in no way disputed in the passage. In fact, this fact is only mentioned in passing in the first paragraph and not debated subsequently.

ii) The argument relating to PAH originating on earth refers only to the poly cyclic aromatic hydrocarbons (PAHs) which are found on the rock and not the meteorite itself.

Moreover, the question pertains to what is true about the meteorite and not about the PAHs which are compounds found on the meteorite.

Hope this helps.
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i agree E is right but why in Q4 C is WRONG?

(C) The PAHs contained in the meteorite would have originated from non-biological processes.


Passage says:
Scientist: Organic decomposition --> PAHs
Skeptics: Terrestrial contamination -->PAHs
Author: scientist (PAHs) --> decay organisms than non-biological

non-biological means not decay organisms --> not biological process
( there can be 2 process only : biological ( related with living things) or non biological ( related with non-living things)
how can a non-biological process is not terrestrial contamination?
If terrestrial contamination then it is not organisms decay contamination. if non organism then it means it is non-biological

what else possibility could be?

Why in Q3, E is wrong

(E) The organic molecules found in ALH84001 could not be the result of terrestrial contamination.
>> Scientists claim that organic material often decays into PAHs which is due to decaying organisms
>>Skeptics claim that PAHs could be the result of terrestrial contamination.

In order to define E wrong, Is it ok to assume Skeptics were also scientist?
GMATNinja CrackVerbalGMAT

Hi

Let me try to address your query.

As per the passage, PAHs are formed when microbes die and their organic material decomposes. The opposition to McKay's conclusions about the PAHs found on ALH84001 is that since it has been on Earth for 13000 years, the PAHs could be from terrestrial contamination. This can to be interpreted to mean that the PAHs found on ALH84001 are a result of contamination from the earth's surface ("terrestrial") and not from Mars ie; they could be from microbes on earth which have died and decomposed. This is definitely a biological process.

Now, coming to question 4, which asks: The passage suggests that if a meteorite contained PAHs that were the result of terrestrial contamination, then one would expect which of the following to be true?

Option (C) states: The PAHs contained in the meteorite would have originated from nonbiological processes.

As can be seen from the above scenario, it is not necessary for terrestrial contamination to result in PAHs that are from non-biological processes. Hence option (C) is incorrect.

Hope this helps.
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My friend, the proximity is the secret to solve such questions at ease. Therefore, find the keyword and read ONLY the previous, and next sentences as well as the one that contains the keyword.

Your promising keyword here is "13,000 years". Let me excerpt the related part in line with my suggestion. Here it is.



Note that terrestrial means from the Earth, which we live on. Option C is a perfect match. If scientists suggest that this meteorite's PAHs might have resulted from terrestrial contamination, that indicates that ALH84001 may not have contained PAHs when it landed on Earth. Note the wording of the option. That is subtle, yet important. It uses "may", claiming the probability, not the certainty.

Option E, on the other hand, implies exactly the opposite of what I described above.

As for option B, , emphasizing that the reading refers to an extra-terrestrial (not from the Earth) phenomenon, the stars, to give an example of the non-organic source, we can safely eliminate this option because it supports that ALH84001 contained PAHs before it landed on Earth.

I hope my answer is clear.

Kudos if you liked this post.
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As for option B,
Quote:
(B) ALH84001 contains PAHs that are the result of nonbiological processes.
, emphasizing that the reading refers to an extra-terrestrial (not from the Earth) phenomenon, the stars, to give an example of the non-organic source, we can safely eliminate this option because it supports that ALH84001 contained PAHs before it landed on Earth.

(B) ALH84001 contains PAHs that are the result of nonbiological processes.
>>processes unrelated to organic life can easily produce all the evidence found by McKay’s team
>> The skeptics’ strongest argument: star formation produces PAHs. Moreover, PAHs frequently appear in other meteorites, and no one attributes their presence to life processes.

Skeptics mention that these formation of PAHs could be due to non-biological process and the same thing may have happened in ALH84001?
It may contain PAHs that could be result due to non-biological process ( as it appear in other meteorites)
WHY NOT CORRECT THEN?
Is it because of CONTAINS rather then MAY contain?

IF option B
ALH84001 contains PAHs that maybe the result of nonbiological processes.
Then would have been CORRECT?





(E) The organic molecules found in ALH84001 could not be the result of terrestrial contamination.

Skeptics claim it could be result due to terrestrial contamination,,
Mc team says : it maybe due to terrestrial contamination on mars,
So organic molecules is due to terrestrial contamination as claimed by scientists
One group of scientists claim it is due to mars land contamination(terrestrial can be for any inner planets – earth, mars etc.)
Others says it is due to earth land contamination
It maybe due to star formation also
So we cannot say “”COULDN’T be results of terrestrial contamination.”
REJECT

IF option E
The organic molecules found in ALH84001 MAY not be the result of terrestrial contamination.Then would have been CORRECT?


(C) ALH84001 may not have contained PAHs when it landed on Earth.
>> some scientists that its PAHs might have resulted from terrestrial contamination
so maybe it didn’t have PAH but PAHs appear because of earth terrestrial contamination . But this combination can be rejected because
“”concentration of PAHs increases as one looks deeper into ALH84001, contrary to what one would expect from terrestrial contamination “”
It means that there was some PAHs before it landed on earth .
But optons says “MAY NOT”

IF OPTION C
ALH84001 doesn’t contain PAHs when it landed on Earth.
Then should be WRONG?

tyildirim92 CrackVerbalGMAT