A question
Where does oxygen come from?
A calm, true answer. Then, if the wondering keeps going, the whole episode.
The short answer
From living things that are mostly green, and mostly somewhere you are not looking. Plants, algae and drifting ocean plankton take in sunlight, water and carbon dioxide, and give off oxygen as what is left over.
About half of it comes from the sea, from phytoplankton far too small to see. So the breath you just took was likely made by something floating thousands of miles away, in water you will never swim in.
Go deeper tonight
Oxygen: Where Does It Come From?
The full episode, in one calm voice, with nothing that startles.
Read the guide for this one in the morning.
This connects to
Air and pressure Living bodies
One idea turns up in many different nights. Follow one and the library starts to join up.