Oxygen – we all need it, we can't live without it. It's integral to life on this planet. And it's probable that, as you watch this film, you will be breathing in an oxygen atom that was also breathed by Genghis Khan – or by the first ever apes to stand upright on the plains of Africa.
The oxygen that we breathe is made from two oxygen atoms joined together – O2. They were first joined more than 3 billion years ago by the earliest blue-green algae to evolve.
Since then, both together and apart, they've had the most extraordinary adventures. Each of the two atoms in an oxygen molecule is virtually indestructible – so they have been first-hand players in some of the most dramatic events in the whole of Earth's history.
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