Passage Summary: Scientists think a giant space rock might have killed the dinosaurs by kicking up so much dust that the Earth cooled down for a long time.

Conclusion: The comet theory is a plausible explanation for why dinosaurs went extinct.

Reasoning: A massive comet impact would generate a global dust cloud, leading to a long-term cooling of the climate that could kill off the dinosaurs.

Analysis: To weaken this, we need to find a reason why a comet impact wouldn't have caused the extinction or why the specific mechanism of cooling via dust is flawed. Perhaps the fossil record shows dinosaurs were already extinct before the comet hit, or maybe the dust cloud wouldn't have lasted long enough to cause a mass extinction. Look for an answer that introduces evidence contradicting the timeline or the environmental effects required for the theory to work.