You just want to argue, don’t you?
No. I’m simply making the point that often the concept of “proof” for some people exceeds the limits of reason. High concentration of oxygen in an atmosphere create a reducing atmosphere the reacts with iron and other common elements. Unless continuously replenished by some mechanism, high amounts of oxygen don’t linger long, geologically, in any atmosphere. Oxygenating mechanisms other than plant life are difficult to describe. High amounts of methane in the presence of oxygen are likewise temporary unless continuously replenished.