The earthquake must HAVE destroyed it “Must have” is a phrase that indicates we have used some other information to deduce what we now believe to be true. For example: Person A: “My daughter graduated at the top of her class!” Person B: “Wow, you must have been proud! Your daughter must have worked very hard.” In this example, Person B used the information that Person A’s daughter graduated at the top of her class to deduce that Person A was proud and that the daughter had worked hard. Another suggestion: I don’t know the context of this sentence, but on its own “the earthquake must have destroyed it years before” still doesn’t sound right because you don’t say WHAT it was before. You could say “The earthquake must have destroyed it years before we arrived” (or years before something else happened). Alternatively, you could say “The earthquake must have destroyed it years ago,” which means years before now.

It's must have. When we use must we use present tense (verb 1).

"must have" is correct. I'm not entirely sure why, a tutor can probably explain haha; but as a native speaker, I can identify the correct one :) 'Had' is typically used like "I had lunch already, or she had two bags with her". I guess 'had' implies possession of something, whereas 'have' in your example describes an action.

Hello! "Must have" is correct. Must is a modal verb which has two past tense forms - "must have" and "had to", so "must had" is incorrect. "Had" is the past perfect form of "have" and would be used on its own like this: The earthquake had destroyed it years before.