Martin Rees writes:
Why are carbon and oxygen atoms so common here on Earth, but gold and uranium so rare? The answer – one of the undoubted triumphs of twentieth-century astrophysics – involves stars that exploded before our Solar system formed. Our galaxy is like a vast ecosystem, recycling gas through successive generations of stars, gradually building up the entire periodic table. Before our Sun even formed, several generations of heavy stars could have been through their entire life cycles, trasmuting pristine hyrdrogen into the basic building blocks of life – carbon, oxygen, iron and the rest. We’re literally the ashes of long-dead stars.
Sound familiar? We’re the biomass of the universe.