Climb to the roof on a clear night, beyond the reach of the city's glow, and count the stars you can see. However far you count, remember this: every one of them — and the roof beneath your feet, and the eyes you are counting with — began as a single element, hydrogen. Everything else on the periodic table was built afterwards, in kitchens you can actually name: the Big Bang, the hearts of stars, exploding stars, colliding dead stars. The chemistry of the universe is a story with four kitchens.
The first three minutes
Thirteen point eight billion years ago the universe began hotter and denser than imagining allows, then cooled as it swelled. By the time it was about three minutes old, it had finished its first and fastest round of element-making: single protons — hydrogen nuclei — everywhere, with roughly a quarter of the material by mass fused into helium and a whiff of lithium. Then the furnaces shut, and for a long time nothing new was made. That early recipe still rules: even today the universe's ordinary matter is about three-quarters hydrogen and one-quarter helium. Nearly everything else — every other box on the periodic table — is a rare latecomer.
Stars: the great kitchens
Gravity gathered the hydrogen into the first stars and squeezed their cores until protons fused into helium, and the darkness lit up. Our Sun runs this same reaction today. But massive stars keep going: helium fuses to carbon, carbon to oxygen, onwards, layer upon layer like an onion, until the core turns to iron. And there the business fails, because fusion up to iron pays out energy while fusion past iron swallows it. An iron core means the engine is out of fuel: the core collapses within a fraction of a second and the star detonates as a supernova — for a few weeks it can shine brighter than its whole galaxy — scattering carbon, oxygen, calcium and iron through space, and forging elements heavier than iron in the blast itself.
Where gold comes from
Even a supernova is not the end of the story. In 2017 the world's gravitational-wave detectors caught two neutron stars — crushed remnants of dead suns — spiralling into each other about 130 million light-years away. Telescopes swung around and watched the crash glow, and written in that light were the signatures of heavy metals: much of the universe's gold and platinum is minted in collisions like this. The gold in a wedding ring is most likely debris from a star-crash that happened billions of years before the Sun was born.
Star-stuff
Our solar system condensed from a cloud of gas already salted with the ash of dead stars — without that inheritance there would be no iron at Earth's core, no iron in your blood, no gold in the jewellers' shops of Tanti Bazar. Carl Sagan put it in four words: we are made of star-stuff. The hydrogen in your glass of water is original Big Bang stock; the carbon in your cells came from a star's furnace; the iron in your blood was cast in a dying giant and delivered by explosion.
So the next clear night, when you are on the roof counting stars, remember that you are not looking at strangers. The hydrogen in you is their oldest sibling; the rest of you is their ash and their inheritance. The sky is not above you so much as around you — family, holding light. Look up, and say hello.