How does carbon dioxide become locked up in carbonate rocks?
Normal wear of tire over the miles, good indication to replace tire. If tire has less than 2500 miles on the front, that means you need to make sure you have the correct tire pressure often.
improper tire pressure, worn brake pads / rotors out of spec, weak fork springs, tweaked forks, bent rim are the first few things that come to mind
sorry mate but without more info i dont see that anyone can help, if the tyre is under or over inflated it will either wear the centre or the edges more.