"All the results of atomic theory are down to random chance, and it's a useless model" [~0%]

"Atomic theory is the absolute best possible model for reality, and handles all edge cases ideally" [~0%]

I'd say 40 decibans is my minimum credence for ANY major established theory, simply due to the possibility of procedural error or unknown factors in any attempted disproof. i.e. I would assume that there's been at LEAST 10,000 erroneous results that purported to disprove the theory.

Alternately, if we assume there are at least a million scientists, and they average 1 test of the theory each, that gives us ~60 decibans.

If we take a common behavior that most of the world has done at least once, that gives us ~90 decibans