You may have heard that we are all stardust, but that isn’t strictly true. There are about 20 different elements in the human body, most of which were made inside ancient stars. There’s oxygen, which makes up about half of your body’s mass but only a quarter of its atoms, and then carbon, accounting for another 12 per cent. And just after that, there’s hydrogen, the only element in your body that wasn’t made inside a star long ago and flung into space by a supernova explosion. The hydrogen atoms in your body, accounting for a little over 10 per cent of you, were formed much earlier during the Big Bang, some 13.8 billion years ago.