LSAT 105 | Section 1 | Logical Reasoning: Q19

LR Question 19 Explanation

QUESTION TEXT: Paleontologist: It is widely, but falsely, held that …

QUESTION TYPE: Strengthen (Exception)

CONCLUSION: The belief that life began in the ocean and didn’t exist on land until half a billion years ago is false.

REASONING:

1. Carbon-14 was found in 1.2 billion-year-old rocks in North America.
2. Carbon-14 is absorbed from the atmosphere by plants and microbes, which release it when they die.

ANALYSIS: If carbon-14 was found in rocks that old, then it must mean that plants and microbes were present at the time. 1.2 billion years ago is a lot longer than 500 million years ago, so plants and microbes must have been on land much earlier than people thought.

Four answers will provide support for the paleontologist’s claim that life existed on land more than a billion years ago. The correct answer will either weaken this hypothesis, or be irrelevant (i.e. neutral or not impact it).

___________

1. This supports the conclusion. If fossils older than half a billion years old exist, this helps strengthen the paleontologist’s claim.
2. Also supports. If conditions in the ocean were too harsh for life to originate there, this strengthens the claim that life may have started on land instead.
3. Also supports. If some portions of the rocks were never submerged, then any C-14 found in them must have come from land-based organisms rather than ocean life.
4. CORRECT. This only tells us how C-14 got into the soil, but not whether life existed on land.
5. Also supports. This confirms the age of the rocks, thus strengthening the claim.