Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

Q: Question: What is the term for the gases that surround a planet? Answer: the atmosphere

A: An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not stable.
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Q: Question: What remains a constant of radioactive substance over time? Answer: rate of decay

A: The rate of decay of a radioactive substance is constant over time.
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Q: Question: What are the highest clouds in the atmosphere? Answer: noctilucent clouds

A:
Noctilucent clouds are the highest clouds in the atmosphere.
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