Passage Summary: Scientists used to think Antarctica was frozen for 14 million years, but they found 3-million-year-old sea fossils under the ice. The author concludes the ice must have melted back then to let the sea in, especially since heat or volcanoes could have done it.

Conclusion: The Antarctic ice sheet must have temporarily melted approximately three million years ago.

Reasoning: Ocean-floor fossils dated to three million years ago were found beneath the central Antarctic ice, and mechanisms like climatic warming or volcanic activity could have caused such melting.

Analysis: The author observes a surprising phenomenon—sea fossils under ice—and immediately concludes that the ice must have disappeared to allow the sea to reach that spot. This is a classic causal flaw where the author ignores other possibilities, such as geological shifts or tectonic movements that could have moved those fossils without the ice melting. When looking for the flaw, focus on the fact that the author treats a possible explanation (melting) as the only necessary explanation. You should anticipate an answer choice that points out the failure to consider alternative ways those fossils could have ended up under the ice sheet.