Passage Summary: Scientists found old sea fossils under the Antarctic ice, leading them to conclude that the ice must have disappeared for a while about three million years ago.

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

Reasoning: The discovery of three-million-year-old ocean-floor fossils beneath the current ice sheet suggests the area was once underwater, which would require the ice to have melted.

Analysis: In this 'Identify the Conclusion' task, we look for the primary claim that the rest of the passage is trying to prove. The word 'therefore' in the third sentence is a major signpost, indicating that the claim about the ice melting is the logical destination of the evidence provided. The first sentence sets the context of previous beliefs, the second provides the new evidence, and the final sentence offers a causal explanation for how the melting occurred. Since the final sentence supports the 'therefore' claim by explaining its possibility, the 'therefore' statement remains the main conclusion.