why can't we humans live without oxygen? Can't we rely on something else? Why? Why oxygen out of all?​

because we need it to breathe

Explanation:

we breathe in oxygen and release carbon dioxide

Ok i have a really weird theory.

Oxygen actually kills us we just don't know it yet. We need it too live but something in it also poisons us and causes us to die in around 100 years from birth. that's why we all die

real answer

we need it to breathe, when we breath we inhale in oxygen and release carbon dioxide which allows trees to grow and they produce more oxygen. We cant rely on anything else because oxygen is important and without it we die. Oxygen is one of the purist airs.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).