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: When volume does not change, temperature is proportional to what other property? Answer: pressure

A: Pressure and temperature at constant volume are directly proportional.
****
Q: Question: What causes blue litmus to turn red? Answer: acid

A: Acids change the color of certain acid-base indicators. Two common indicators are litmus and phenolphthalein. Blue litmus turns red in the presence of an acid, while phenolphthalein turns colorless.
****
Q: Question: How many years ago may the earliest fungi have evolved? Answer: 600 million

A:
The earliest fungi may have evolved about 600 million years ago.
****