First of all it is spelled 'Oxygen'.
It is not that Earth's Oxygen is more breathable than another planet's. We have just evolved to need Oxygen to live. Other planets don't have as much Oxygen as we need to live. They have other gases that would kill us instantly. That is why we need spacesuits to be able to walk on the moon and other planets. The same goes for Outer Space. Outer Space has no Oxygen at all.
The earths atmosphere is made up of 78% nitrogen and 21% oxygen
is it oxygen
97%
Yes
no
Oxygen gas
Free oxygen
Plants
oxygen
Oxygen.
47 % oxygen & 27% silicon.
Oxygen is most commonly found in the air of Earths atmosphere.