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.

Question: What remains a constant of radioactive substance over time? Answer: rate of decay
The rate of decay of a radioactive substance is constant over time.

Question: Cirrus, stratus, and cumulus are the main types of what? Answer: clouds
Clouds are classified on the basis of where and how they form. Three main types of clouds are cirrus, stratus, and cumulus. Figure below shows these and other types of clouds.

Question: Where do archea live? Answer: everywhere
Archaea live everywhere on Earth, including extreme environments.