What is the adverb in the following sentence? "Soon it will be getting dark."

(An adverb modifies a verb, (answering how, why, when, etc.)  Here, the verb is “will be getting” (properly, a verb plus auxiliaries).  The word “Soon” modifies the verb by answering the question “When will it be getting dark?” It will be getting dark soon.  Therefore the adverb in this sentence is “soon.”  It may be a little confusing because the adverb usually follows the verb, as in “the bus is coming soon.”  Also, the verb here is a future tense verb, “will be coming.”  When the verb is in the present or past tense, and active, as in “The ball bounces easily” or “The ball bounced high,” the adverb is more easily identified.  Also, when an adverb ends in “-ly” as in “easily,” it stands out in a sentence because the "ly" suffix is the signature way to modify an adjective into an adverb (easy - easily).  Another confusion is the word “dark.”  This is a predicate adjective describing “it.”  Some grammarians (influenced by Noam Chomsky) would treat “getting” as the verb and “will be” as fragments, or would use the phrase “verb plus prep” to name this a predicate phrase, with an adverb.