For this chain-of-thought reasoning and answer, what was the question?
Rocks widest variety is found on earth. Question mentions about planets and moons, so earth is the most appropriate answer.
 A: surface of earth
Q: Rocks can be found on many planets and moons, but we know of the widest variety of them on the what?
Options:
- ground
- waterfall
- surface of earth
- museum
- atmosphere