Early may function either as an adj or an adv. (Earlier is the comparative degree form)
Before functions as a preposition, as a conjunction or an adverb.
As you can see they overlap only when used as an adverb.
e.g. Why didn't you come earlier / before?
But: Can we meet at an earlier hour? (adj)
Can we meet before lunch? (preposition)
Can we meet before you leave for London? (conjunction)

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