Question: Where did oxygen come from

Jake answered on 9 Dec 2020:

All the oxygen we breathe, as well as almost everything that makes up the Earth, was originally made in the middle of an exploding star! When the Earth first formed all that oxygen was trapped inside rocks, so there wasn’t any in the air to breath. Over millions of years living things have changed the atmosphere, and now it’s full of oxygen, which makes Earth a great place for lots of things to live!