We not only live in the air, we live because of it. And air is about much more than just breathing. It is a transformer and a protector, though ultimately also a poison.
At ground level, photosynthesis transforms air miraculously into solid food without which every creature on Earth would starve.
It wraps our planet in a blanket of warmth. It brings us wind and rain and fire. It sustains our bodies and at the same time it burns them up, slowly, from the inside.
The atmosphere provides a floating mirror for intercontinental radio signals and its outer layers soak up flares of deadly radiation from the Sun.
In the first episode of this three-part series, Gabrielle Walker experiences air - and weighs it.
At ground level, the air is not as 'thin' as we might imagine. The Royal Albert Hall, in its day one of the largest volumes of air enclosed in a single span may seem to be full of nothing, but in fact, the air inside weighs 30 tons.
On the other hand, not much further away than the next city, the air is so tenuous as to be unbreathable. That is in the 'up' direction.
In between is a gaseous ocean in which Gabrielle takes a swim - floating on air, flying a glider and chasing the storm clouds that bring us our weather.