Question

Where does air comes

Answer 1

since 500 millions years ago oxygen has been the 21℅of our air.

Answer 2

Heyaa folk,

Air forms on the earth, many many years ago (500 million years). Its proportion, we can arrange as follows-
• Nitrogen : 78%
• Oxygen : 21%
• Other gaseous : 1%.

[ Other gaseous formed by water vapour, CO2 i.e. Carbon Dioxide, etc. ]

Hope it helps u :)
- no4 ✯ Brainly Star ✯