The correct answer is (D).
(D) Weaken
Step 1: Identify the Question Type
This is a clear Weaken question stem. The correct answer will make the geologist's conclusion less likely to follow from her evidence.
Step 2: Untangle the Stimulus
In this stimulus, you must keep track of various opinions. First, you get some helpful background: The dominant view holds that petroleum was formed from plant and animal remains deep in the Earth's crust. The geologist concludes that the theory of those challenging the dominant view has been refuted; i.e., she believes that the dominant view is correct. Her evidence is that biomarkers (molecules indicating living organisms) are found in petroleum. For the geologist's argument to work, she must assume that the biomarkers came from the remains of plants and animals deep in the Earth's crust.
Step 3: Make a Prediction
A fact suggesting that the biomarkers are not from the remains of plants and animals deep in the Earth's crust will weaken this argument. Remember, the correct answer will weaken the geologist's position, and thus the dominant view. The correct answer strengthens the theory of those who challenge the dominant view.
Step 4: Evaluate the Answer Choices
(D) is correct. It weakens the geologist's argument by suggesting that the biomarkers found in petroleum might come from a source other than the remains of plants and animals deep in the Earth's crust. Those who challenge the dominant view would welcome the fact in (D) .
(A) is Outside the Scope. The geologist is using the presence of biomarkers to argue that petroleum is formed from the fossil remains of plants and animals. Fossils without biomarkers have no impact on her argument. The fact in (A) suggests another avenue of investigation perhaps, but one that would, if proven, strengthen the geologist's argument.
(B) is Outside the Scope. The geologist does not claim that petroleum dates to the formation of the Earth, and those who challenge the dominant view don't believe that petroleum comes from fossils, so the fact in (B) is moot for both sides of this debate.
(C) is Outside the Scope. Much like the fact in (B), the statement here is not one with which either side in the debate would take issue. It simply doesn't impact either theory.
(E) is Outside the Scope. Again, as with the facts in (B) and (C), everyone involved in the debate could agree with this statement without altering their points of view. The geologist and those who hold the dominant view would say, "This is true, and these are the deposits from which petroleum is formed." Those who oppose the dominant view would say, "Yes, it is true, but those are not the deposits from which petroleum is formed."
