In 1994, a team of scientists led by David McKay began studying the meteorite ALH84001, which had been discovered in Antarctica in 1984. Two years later, the McKay team announced that ALH84001, which scientists generally agree originated on Mars, contained compelling evidence that life once existed on Mars. This evidence includes the discovery of organic molecules in ALH84001, the first ever found in Martian rock. Organic molecules—complex, carbon-based compounds— form the basis for terrestrial life. The organic molecules found in ALH84001 are poly cyclic aromatic hydrocarbons, or PAHs. When microbes die, their organic material often decays into PAHs.


Skepticism about the McKay team’s claim remains, however. For example, ALH84001 has been on Earth for 13,000 years, suggesting to some scientists that its PAHs might have resulted from terrestrial contamination. However, 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 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.

1. The primary purpose of the passage is to:

(A) describe new ways of studying the possibility that life once existed on Mars
(B) revise a theory regarding the existence of life on Mars in light of new evidence
(C) reconcile conflicting viewpoints regarding the possibility that life once existed on Mars
(D) evaluate a recently proposed argument concerning the origin of ALH84001
(E) describe a controversy concerning the significance of evidence from ALH84001

2. The passage asserts which of the following about the claim that ALH84001 originated on Mars?

(A) It was initially proposed by the McKay team of scientists.
(B) It is not a matter of widespread scientific dispute.
(C) It has been questioned by some skeptics of the McKay team’s work.
(D) It has been undermined by recent work on PAHs.
(E) It is incompatible with the fact that ALH84001 has been on Earth for 13,000 years.

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?

(A) ALH84001 may not have originated on Mars.
(B) ALH84001 contains PAHs that are the result of nonbiological processes.
(C) ALH84001 may not have contained PAHs when it landed on Earth.
(D) The organic molecules found in ALH84001 are not PAHs.
(E) The organic molecules found in ALH84001 could not be the result of terrestrial contamination.

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.

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.

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

(A) These PAHs are not likely to be found in any meteorite that has been on Earth for 13,000 years or more.
(B) These PAHs are not likely to be found in any meteorite that originated from Mars.
(C) These PAHs are not likely to be produced by star formation.
(D) These PAHs are likely to be found in combinations that distinguish them from the PAHs produced by organic processes.
(E) These PAHs are likely to be found in fewer meteorites than the PAHs produced by organic processes.