You're right about "naturally" and "elements", but "occurring" is actually a verb participle that is modifying "elements". So we have the noun phrase: "naturally occurring elements".
It's usually adjectives that modify nouns, but sometimes verbs can do that too, for example:
A sleeping child. The condemned man. The gleaming showroom.
In those examples, the verbs "sleeping" and "gleaming" are present participles, and "condemned" is a past participle. They are not actually adjectives as such, but they are all modifying nouns, just like 'real' adjectives would do.
You're right about "naturally" and "elements", but "occurring" is actually a verb participle that is modifying "elements". So we have the noun phrase: "naturally occurring elements".
It's usually adjectives that modify nouns, but sometimes verbs can do that too, for example:
A sleeping child. The condemned man. The gleaming showroom.
In those examples, the verbs "sleeping" and "gleaming" are present participles, and "condemned" is a past participle. They are not actually adjectives as such, but they are all modifying nouns, just like 'real' adjectives would do.
Yes, the adverb "naturally" modifies "occurring". As a noun modifier, we call "naturally occurring" a VP (verb phrase. Here are some more VPs comprising adverb-verb combinations:
A recently discovered fossil. His recently published article. The rapidly melting ice cream.