How old are you? You Are 4.5 Billion Years Old
Did you answer with a number less than a hundred? Of course you did. We're taught from an early age to start counting from the year we were born. That's a legitimate way to do it. It's also boring, and it hides something extraordinary about the body you're sitting in right now.
The truth is, you are as old as the Earth itself. Probably older. But let's settle for the age of the Earth to start.
Look at your hand. Run your fingers across your face. Take a breath and feel your lungs expand. What you're touching, what you're seeing, what you're breathing with — all of it has been here on this planet for four and a half billion years. You are 4.5 billion years old.
Your body and mine are made of trillions of atoms, and those atoms don't simply wear out or stop. They get rearranged. Endlessly. Every atom in your body — the carbon in your skin, the iron in your blood, the calcium in your bones — has been here since long before there was an Earth to stand on. Not a single atom is younger.
Now that's magic.
It's a hard idea to hold in your head. That every part of you is made of something as old as the planet. But the magic doesn't stop there. It gets stranger.
You are not the first to use these atoms.
The atoms that make up your eyes, your feet, your lungs, your brain — every part of you — have been used millions of times before. Probably hundreds of millions. By oceans. By dinosaurs. By insects and trees and thunderstorms and mountains. Among all the atoms in your body, you almost certainly carry at least one for every kind of thing that has ever existed on this planet.
And within your DNA are strands traceable to the very first speck of life that ever appeared on this planet. If a scientist could pull DNA from the earliest humans, from a Neanderthal or a Cro-Magnon, they would find sequences that match yours identically.
That's magic. Your atoms have been spinning for 4.5 billion years, and they don't stop.
And if you trace those atoms back further still — before the dinosaurs, before the oceans, before Earth itself — they were forged inside stars. The iron in your blood, the calcium in your bones, the oxygen filling your lungs right now: all of it was cooked in the cores of giant stars that lived their long lives and exploded, scattering their guts across the galaxy long before our sun ever began to burn. The hydrogen in the water of your body — and you are about 60% water — is older still. It has been here since roughly 380,000 years after the Big Bang, almost 13.8 billion years ago. You are made of stardust, and part of you is nearly as old as the universe itself.
Here's something else strange.
Most of you flows. Some of you stays.
Among all the atoms in your body, you almost certainly carry at least one for every kind of thing that has ever existed on this planet — and the deepest record of that lineage is written inside you. Your body is mostly turnover — water cycling through every couple of weeks, skin replacing itself every month, your liver remade every few months. But some of you is permanent. The neurons in the cerebral cortex you're using to read this sentence have been with you since infancy, and the atoms locked in their DNA were captured on the day those cells were born. The cells at the center of your eye lenses — the very cells focusing light onto this page — were formed before you were born. They have never been replaced. They will never be replaced. They are older than your earliest memory and they will be the last things in you to die.
So what are you, really?
You aren't a thing. You're a pattern. A standing wave. A particular arrangement of ancient matter that flows through you like water through a riverbed. The riverbed has shape and identity even though no two moments of water are the same.
You are a 4.5-billion-year-old riverbed that the universe is pouring through.
So how old are you?
You can keep using the answer you've always given — the number that starts from your birthday. There's nothing wrong with it. It's the answer the world expects.
But you and I now know better.
Think about what that means. The atoms inside you right now have been places. They have been things. They have done what the things of Earth do.
Some of the atoms in your hand were once swimming in the warm, shallow seas of the Cambrian, locked inside the shell of a trilobite. Some were in the muscle of a dinosaur — a Triceratops drinking from a river, an Allosaurus running down its prey. Some were in the wet bark of the great Carboniferous swamps, the forests of giant ferns that would, over hundreds of millions of years, compress into the coal we still pull from the ground today. Atoms inside you were once mosquitoes in the age of reptiles. Once schools of fish in seas that no longer exist. Once feathers on the first birds to figure out the sky. Once leaves on trees that fell before any human ever walked the Earth.
The atoms in your bones have been mountains — the old, weathered Appalachians when they were young and tall as the Himalayas. They've been the ash of volcanoes that buried whole landscapes. They've been the silt of rivers that ran across continents that no longer exist in the shapes we know. They've been the floor of the ocean, then lifted up, then ground down again into sand, then carried in the wind, then drunk by something, then breathed by something else, then eaten by something else, then arranged — for now, briefly — into you. There are atoms inside you that were kicked up into the atmosphere by the meteorite that ended the dinosaurs.
And the atoms in you have been people. There is no way around this. The atoms of your hand have been the atoms of other people's hands. They've been the hands of farmers in the first agricultural villages, of warriors at Thermopylae, of scribes in ancient Egypt, of mothers nursing children in caves we will never find. They have been the lungs of the people who built Stonehenge and the eyes of the people who watched the Library of Alexandria burn. They have, almost certainly, been parts of someone you would recognize from a history book — and parts of millions of people whose names were never written down at all.
You are made of dinosaurs and oceans and ancestors. And imagine: the dinosaurs, oceans, and ancestors' atoms that made you up yesterday will be replaced in a few weeks by an entirely new set of dinosaurs, oceans, and ancestors. The history doesn't run out. It just keeps flowing through you.
So, you see? You're not 47, or 63, or 28.
You are 4.5 billion years old. You are wearing the atoms of everything that has ever been alive on this planet, and when you set them down, something else will wear them next. And the atoms don't stop when you do.
That's magic.
