A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended...
GMAT Critical Reasoning : (CR) Questions
A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.
Which of the following would, if true, provide the most additional support for the scientists' conclusion?
Passage Analysis:
| Text from Passage | Analysis |
| A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. |
|
| The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. |
|
| Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged. |
|
Argument Flow:
The argument starts with a surprising discovery, explains why it's puzzling given what we thought we knew, then presents scientists' explanation for how this could have happened.
Main Conclusion:
Scientists conclude that the sea-level rise 25 million years ago left at least part of Marlandia unsubmerged.
Logical Structure:
The logic works like this: If modern reptiles are descended from ancient ones (fossil evidence), and those ancient ones were supposed to have died out when islands went underwater (established belief), then the only way the descendants could exist today is if some land stayed above water for the ancestors to survive on.
Prethinking:
Question type:
Strengthen - We need to find new information that would increase our belief in the scientists' conclusion that at least part of Marlandia remained unsubmerged during the sea-level rise 25 million years ago.
Precision of Claims
The key claim is about geographical conditions - specifically that 'at least part of Marlandia' stayed above water during a specific time period (25 million years ago). This is a claim about the extent/scope of submersion during a historical event.
Strategy
To strengthen the conclusion that some land stayed dry, we need evidence that supports this scenario. We can think about: (1) Direct evidence about the reptiles' survival requirements, (2) Evidence about the geographical conditions during that time, or (3) Evidence that rules out alternative explanations for how the reptiles could have survived total submersion.
'Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.' This tells us about the reptiles' general adaptability over the past 25 million years, but it doesn't specifically support the idea that land remained unsubmerged during the sea-level rise. In fact, highlighting their adaptability might suggest they could have survived total submersion, which would weaken rather than strengthen the scientists' conclusion.
'Marlandia separated from a much larger landmass about eighty million years ago.' This gives us geological history from 80 million years ago, which is much earlier than the relevant 25-million-year-ago sea-level rise. This information doesn't help us understand what happened during the specific event that the scientists are trying to explain.
'No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.' This suggests the evolutionary relationship is unique to Marlandia, but it doesn't strengthen the conclusion about whether parts of Marlandia remained dry. The scientists could still be wrong about land remaining unsubmerged - there could be other explanations for how the reptiles survived.
'The present-day reptiles are able to thrive on very tiny Marlandia islands.' This shows that modern reptiles don't need much land space, which supports the idea that even small unsubmerged areas could have sustained their ancestors. However, this is relatively weak support since it doesn't address whether such areas actually existed or whether the reptiles could have survived without any dry land at all.
'The ancestral reptiles could not have survived long at sea.' This provides crucial information that directly strengthens the scientists' conclusion. If the ancestral reptiles couldn't survive in water for extended periods, then the only plausible explanation for their descendants' existence today is that some dry land remained available during the sea-level rise. This eliminates the main alternative explanation (that they survived total submersion) and makes the 'partial submersion' conclusion much more compelling.