If that is your FH rubber and you are pushing with your BH and the edge of the racket/rubber touches the table, you might find that kind of wear at the edge.
I am not sure that is what the wear is from. But that looks like topsheet wear from abrasion, not oxidation from exposure to the air (oxygen).
Oxidation can look like nothing but the rubber is more brittle (less elastic) and less grippy. Oxidation could happen in an area on the rubber that has experienced more abrasive wear. But it would be more likely that, in areas of high abrasion, the rubber that has been worn off would be the rubber that was exposed to oxygen. The rubber underneath that is now exposed would likely have less oxidation than the rubber that has worn off the topsheet.