Could We Breathe Something Other Than Oxygen? 

Many of you have probably wondered if you could survive with breathing something but oxygen.  Humans need oxygen to provide nutrients to all of the cells in their bodies. If tissues and cells go without oxygen, then they begin to die quickly. Many gases are toxic to us, even having move than 50% oxygen in gas mixtures if its' pressurized could make that oxygen toxic. 

Ozone consists of three oxygen atoms, instead of two we usually find in air we breathe and its dangerous to even be exposed to it.  Because of the strongly oxidizing properties of ozone, ozone is a primary irritant, affecting especially the eyes and respiratory systems and can be hazardous at even low concentrations. 

On Earth there are no gases we can breathe unless in the future we completely genetically modify human structure to support breathing  other gases that very well could be most of the atmosphere of another planet. But until then we will breathe some O2.