I'll give you a question, please answer with step-by-step reasoning process.
Rocks can be found on many planets and moons, but we know of the widest variety of them on the what?\nOptions:\n- ground\n- waterfall\n- surface of earth\n- museum\n- atmosphere

surface of earth
Rocks widest variety is found on earth.

Question mentions about planets and moons, so earth is the most appropriate answer.

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So, the final answer is surface of earth