"Naturally occurring" means existing by nature and without man's assistance as opposed to "synthesizing" to make (something) by synthesis, especially chemically. There are 93 naturally occurring chemical elements.

There are 118 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from other elements). Of these 118 elements, 94 occur naturally on Earth. The other 24 have been synthesized -- they were man-made.

Plastic is material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be molded into solid objects BUT do nor occur naturally, they are man-made.

The experiments that you have shared with me -- are scientists trying to synthesize polymers through processes that naturally cannot occur. Yes, they can be synthesized but could never naturally evolve.

Earth’s atmosphere is oxidizing (i.e., oxygen rich) and naturally prohibits the spontaneous formation of biomolecules outside the protection of a living cell.

Water forms a natural chemical barrier to the formation of chains of nucleotides such as RNA and DNA that are the foundation of life.