Carl Sagan’s famous ‘star stuff’ quotation takes a simple scientific fact and gives it a uniquely poetic sound. In the earliest universe, after the Big Bang, the only elements to be found were hydrogen and helium. These, of course, came together to form stars, giant nuclear fusion reactors that combined hydrogen atoms to make even more helium. As stars get more massive, they gain the ability to fuse this helium into heavier atoms like carbon, nitrogen, sulfur, etc. up until they reach iron.
Iron is a crucial element in nuclear fusion as it is the lightest element encountered where the energy input needed to fuse it is greater than the energy output of the reaction—ultimately triggering a gravitational collapse in the stars leading to a supernova. This extremely brief gravitational collapse before the supernova is the only time when stars can create elements heavier than iron, explaining why precious metals such as gold and silver are so rare in nature.
The supernova that occurs at the death of these massive stars allows them to disperse all of the elements that they have fused in their lifetimes into space, allowing for the formation of planets such as Earth and everything on them. It is in the hearts of the stars that our atoms were forged and in their dying gasps that these atoms were released into the universe to ultimately end up on this planet for our bodies to use.
Neil deGrasse Tyson will pick up where Carl Sagan left off, distilling complex scientific ideas into a digestible form as he hosts the reboot of COSMOS.