You're on the right track! Oxygen is a byproduct of a very important process called photosynthesis.

Here's how it works:

* Plants and some algae use sunlight, water, and carbon dioxide to create their own food (sugars). This process is called photosynthesis.

* As a byproduct of this process, they release oxygen into the atmosphere.

So, while we breathe in oxygen, it's actually plants and algae that are responsible for producing most of the oxygen we need to survive.