thingocanhnguyen
Hi all,
Any one can help me explain the answer of question 4. My answer is B, not E (OA). What is wrong in B? Why is E correct?
Quote:
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?
(A) The meteorite would have been on Earth for more than 13,000 years.
(B) The meteorite would have originated from a source other than Mars.
(C) The PAHs contained in the meteorite would have originated from nonbiological processes.
(D) The meteorite would contain fewer PAHs than most other meteorites contain.
(E) The PAHs contained in the meteorite would be concentrated toward the meteorite’s surface.
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.
RMD007
Can anyone explain me Question - 5.
Quote:
5. Which of the following best describes the function of the last sentence of the first paragraph?
(A) It identifies a possible organic source for the PAHs found in ALH84001.
(B) It describes a feature of PAHs that is not shared by other types of organic molecules.
(C) It explains how a characteristic common to most meteorites originates.
(D) It suggests how the terrestrial contamination of ALH84001 might have taken place.
(E) It presents evidence that undermines the claim that life once existed on Mars.
I was confused between option A and option B.
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!