- Everyone at the beach would immediately get sunburn (even though there would be no beach, no sand, and no water), because molecular oxygen in the air protects our skin against UV light.
- The daytime sky would get dark, fewer particles to bounce light means a dark almost black sky.
- All pieces of untreated metal would instantly spot weld to each other, the only thing preventing metal from welding together on contact is a layer of oxidation.
- The earth's crust would crumble, as oxygen makes up 45% of the earth's crust.
- Everyone's inner ear would explode, because we would lose about 21% of the air pressure.
- Buildings made of concrete would turn to dust, oxygen is an important binder in concrete.
- Water is a third oxygen, without it hydrogen would turn into a gaseous state and expand in volume.
- The oceans would evaporate and bleed into space.
- Without oxygen, hydrogen is free to float to the upper troposphere and eventually into space.
To be positive, now, what if the amount of oxygen doubled...
- Paper airplanes would fly further.
- We would get better gas mileage.
- Extra oxygen would improve our cognition, alertness, and physical performance.
(Also, there would be giant insects, as an insect's body size is determined by the proportion of oxygen in the atmosphere.)
