All concrete collapsing, massive drops/increases in pressure that can shatter your eardrums, untreated metals cold welding, full UV rays going through an Ozone layer that no longer exists, planes fall out of the sky… oh and yeah the Earths mantle just fucking collapsing in on itself and essentially dissolving as its composition has an enormous amount of oxygen
“There will be no difference in air pressure”
This isn’t really true, the atmosphere just got much lighter since O2 is a bit more than 21% of the mass of our atmosphere.