instruction:
Turn the given fact into a question by a simple rearrangement of words. This typically involves replacing some part of the given fact with a WH word. For example, replacing the subject of the provided fact with the word "what" can form a valid question. Don't be creative! You just need to rearrange the words to turn the fact into a question - easy! Don't just randomly remove a word from the given fact to form a question. Remember that your question must evaluate scientific understanding. Pick a word or a phrase in the given fact to be the correct answer, then make the rest of the question. You can also form a question without any WH words. For example, "A radio converts electricity into?"
question:
Fact: isotopes are used to determine the age of fossils.
answer:
what is used to determine the age of fossils?


question:
Fact: Plants use fiber for their cell walls.
answer:
Plants use what for their cell walls?


question:
Fact: natural gas is formed from layers of sediment covering the remains of organisms over time.
answer:

What is formed from layers of sediment covering the remains of organisms over time?