Long after Big Bang nucleosynthesis, more complex elements formed through a variety of processes. Stars are nuclear fusion reactors — engines that fuse lighter elements together into heavier ones. The process of fusion itself creates many more elements on the periodic table, up to iron and nickel. Exploding stars — supernovae — are the dying carcasses of massive stars far heavier than the Sun. Their bombastic blasts create heavier elements still, and the blasts send them far out into the surrounding galaxy. These processes, over vast amounts of time, have created and spread the variety of elements, most far heavier than hydrogen and helium, that we know of today, including the stuff that makes up our bodies.
The cosmic origins of the elements, then, are varied. About two dozen elements originate from dying low-mass stars. These include carbon, nitrogen, strontium, and tin. Another two dozen or so elements come mostly from supernovae. These include oxygen, potassium, sodium, arsenic, and aluminum. Two elements arise from cosmic ray fission — when energetic particles from space impact Earth’s atmosphere and surface. This process creates boron and beryllium.
About another two dozen elements are created largely from merging neutron stars — the clashes of super-dense, dying stellar remnants made mostly of packed neutrons. These include iodine, xenon, cesium, platinum, and gold. And a small number of elements are created, or at least can be created, by exploding white dwarf stars, the final, decayed ultra-dense remnants of stars like the Sun. These include titanium, vanadium, chromium, manganese, iron, and nickel.
These are incredible facts to ponder as you walk out under a starry sky on a clear, moonless night. Look deep toward the shimmering glow of the Milky Way, and you’ll see many twinkling stars and the unresolved light from millions more that make up the hazy band running across our sky. That oldest of all human questions — “Why am I here?” — actually has an answer. You’re here because atoms created in the Big Bang and in the bellies of stars have recombined in a way to make you, billions of years after their creation — with a big thank you to your parents as well.