Oxygen appeared on Earth over two billion years ago and life took off. Now it makes up just over a fifth of the air. Trevor Cox, professor of acoustic engineering at the University of Salford, England, tells the story of oxygen on Earth and in space. Without oxygen, there would be no life on Earth, yet it was not discovered until late in the 18th Century. During the Great Oxidation Event, three billion years ago, cyanobacteria, thought to be the earliest forms of life on our planet, started to photosynthesise and these tiny creatures were responsible for putting the oxygen into our atmosphere, so we can breathe today. But it is not just for breathing. Ozone is three atoms of oxygen, and when it is in the stratosphere it stops harmful UVB rays from the sun reaching us. And if we are ever to leave our home planet, we will need to find a way to generate enough oxygen to keep us alive. Trevor visits the Science Museum in London, to discover how astronauts on the space station get their oxygen. Trevor Cox is not only an acoustic engineer, he also plays the saxophone. When he finds out the role that oxygen, in the air, has on the sound of his playing he gets a surprise.(Photo: Hovering clouds near Nagqu, approx 4,500 meters above sea level, north of Lhasa on the Tibetan plateau. Credit: Frederic J Brown/ AFP/Getty Images)

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