[Cushman]

That you think that unsourced opinion piece constitutes "secondary corroboration" indicates that perhaps you do not, in fact, understand when citation is needed.

[pretoriusB]

Ever tried looking around you? Do you need a citation that air is important for breathing?

[Cushman]

Funnily enough, I can't see air, and if you could not provide any other evidence for its existence I would be extremely skeptical.