LSAT Explanation PT 35, S1, Q17: On the basis of the available

LSAT Question Stem

The reasoning in the argument is most vulnerable to which one of the following criticisms? 

Logical Reasoning Question Type

This is a Flaw question. 

Correct Answer

The correct answer to this question is E. 

LSAT Question Complete Explanation

The question type for this problem is a Flaw question, which asks us to identify the flaw in the argument's reasoning.

First, let's break down the argument in the passage:

1. Antarctica is believed to have been covered by ice for at least the past 14 million years (premise).

2. Recently, three-million-year-old fossils, usually found only in ocean-floor sediments, were discovered under the ice sheet in central Antarctica (premise).

3. The Antarctic ice sheet must have temporarily melted about three million years ago, as either severe climatic warming or volcanic activity could have melted the ice sheet, raising sea levels and submerging the continent (conclusion).

The argument assumes that the presence of fossils typically found in ocean-floor sediments is only possible if Antarctica was submerged due to the melting of the ice sheet. However, there could be other explanations for the presence of these fossils that the argument does not consider.

An "Evaluate" question for this argument could be: "Are there any other possible explanations for the presence of these fossils in Antarctica besides the melting of the ice sheet?"

Now let's analyze each answer choice:

a) The argument does not rely on the widely believed position to establish its conclusion as true. Instead, it challenges the widely held belief with new evidence. This answer choice is incorrect.

b) The argument does not claim that the two possible causes (severe climatic warming or volcanic activity) could not have operated together. The flaw lies in assuming that these are the only explanations for the presence of the fossils. This answer choice is incorrect.

c) The argument does not confuse establishing the occurrence of an event (the melting of the ice sheet) with establishing its cause. The flaw is in assuming that the presence of the fossils necessarily means the ice sheet melted. This answer choice is incorrect.

d) The issue with the fossil evidence is not that it is too "narrow." The problem is that there could be multiple explanations for their presence in Antarctica, but the argument only considers one possibility. This answer choice is incorrect.

e) This answer choice correctly identifies the flaw in the argument. The argument treats the discovery of the fossils as having only one possible explanation (the melting of the ice sheet) when there could be other explanations. This answer choice is correct.