Question

where our oxygen comes from

Answer 1

Our oxygen comes from trees.

Tress take co2 and and release oxygen but in night they take oxygen.

Answer 2

The ocean is the most powerful force on the planet. It feeds us and all around us. And yet, while it gives us 70% of the oxygen we breathe,
In photosynthesis, plants capture sunlight and use its energy to split carbon dioxide and water, making sugar for itself and releasing oxygen as a by-product.