History of chlorine

The chlorine atoms in our swimming pools were forged billions of years ago in ancient stars, according to new research by NASA scientists on the history of chlorine.

As the Earth formed 4.6 billion years ago, it swept up some of that chlorine and incorporated it into its rocks. It can now be sourced from our oceans - they contain about 20 million billion tonnes of it - and also places like Death Valley in California, which was formed from ancient evaporated seas.

Image credit: AirmanMagazine; Flickr