Billions of years ago exploding stars sent atoms hurtling through space and we've been recycling them on Earth ever since. Except for the occasional comet, meteor, some interstellar dust, we've used exactly the same atoms over and over since the Earth was formed. We eat them, we drink them, we breathe them, we are made of them. At this precise moment each of us is exchanging our atoms with everyone else, and not just with each other, but with other animals, trees, fungi, moulds -