#24 - Biologist: Scientists have discovered fossilized

[Administrator]

Complete Question Explanation

Method of Reasoning—AP. The correct answer choice is (C)

The structure of this argument is very complex, with four premises, two subsidiary conclusions, and a main conclusion. The length of this stimulus and its complicated logical structure make this question difficult, and hard to analyze quickly.

The biologist discusses evidence of fossilized bacteria discovered in rocks 3.5 billion years old. These bacteria were complex, indicating their long evolutionary history. Given that Earth is only 4.6 billion years old, the bacteria’s long evolutionary history implies that life on Earth must have begun soon after the planet’s formation, at a time when conditions were extremely harsh. From this evidence, the biologist concludes that life may be able to arise under many difficult conditions throughout the universe. Here is how the argument proceeds:

• Premise: Scientists have discovered fossilized bacteria in rocks 3.5 billion years old.
  
  Premise: The fossils indicate these bacteria were quite complex.
  
  Sub-Conclusion: So, the bacteria must have already had a long evolutionary history when
  fossilized 3.5 billion years ago
  
  Premise: Earth is only 4.6 billion years old.
  
  Sub-Conclusion: So, the first life on Earth must have formed soon after the planet’s formation.
  
  Premise: After the planet’s formation, conditions on Earth were extremely harsh.
  
  Conclusion: therefore, life may be able to arise under many difficult conditions throughout
  the universe

This question stem in this Method of Reasoning—Argument Part question asks you to identify the role played in the argument by the claim, italicized above, that the fossilized bacteria discovered in the rocks 3.5 billion years ago must have had a long evolutionary history. Your prephrase is that this is a subsidiary conclusion that supports another subsidiary conclusion, which itself then supports the argument’s main conclusion.

Answer choice (A): This answer choice is incorrect because it incorrectly states that the claim is not supported by other evidence. It also fails to properly describe how the claim itself is then used in the argument.

Answer choice (B): This answer choice is incorrect because the cited claim is supported by the first two premises. If fossilized bacteria in rocks are 3.5 billion years old, and the bacteria are quite complex, then it logically follows that they've had a long evolutionary history.

Answer choice (C): This is the correct answer choice. As stated above, this claim is a subsidiary conclusion that supports another subsidiary conclusion, which itself then supports the argument’s main conclusion.

Answer choice (D): This answer choice is incorrect, because it incorrectly states that the claim does not support any other claim in the argument. It does.

Answer choice (E): This answer choice incorrectly states that the claim supports two distinct
conclusions,neither of which is designed to support the other. Instead, this claim provides support for another subsidiary conclusion, which then provides support for the main conclusion.

[LSAT student]

Hello,

Is "so" a sub-conclusion indicator here? And when I see it in a stimulus should I generally think of it as such?

[Adam Tyson]

"So" is a conclusion indicator, and as such can indicate either a main conclusion or an intermediate, aka subordinate or subsidiary, conclusion. Whether it is main or intermediate all depends on the structure of the argument. Did the author use that claim to support some other claim? If so, then the claim cannot be the main conclusion and so is likely to be subordinate. If not, you are probably looking at the main conclusion, whether or not there is an intermediate conclusion elsewhere in the argument.

The same holds true for any conclusion indicator, like "hence" and "therefore" and "as a result," etc. They aren't unique to any particular type of conclusion, but can be used to indicate any conclusion, whether main or not.