You are stardust: The long view of when your existence really began

The point when you began depends on the scale you look at and how you define a person – in one sense you’re as old as the universe, in another you’ve hardly begun at all

By Daniel Cossins

When did you begin?

YOU almost undoubtedly know the date, possibly even the hour, you were born. Whether you are past celebrating rather depends. But reflect on the big picture, and the truth about when you began is too epic, and possibly a little too confusing, to be captured by a terse entry on a birth certificate.

That story begins in the deep cosmos. As anyone with a passing interest in Joni Mitchell’s back catalogue knows, we are stardust. It’s a nice line, and it also happens to be true, says Karel Schrijver, an astrophysicist at the Lockheed Martin Advanced Technology Center in California.

Most of your body’s trillions of atoms, from calcium in your bones and carbon in your genes to iron in your blood, were forged by nuclear reactions in ancient stars, either when they were burning or when they ended in fiery supernova explosions. Those atoms were recycled through the births and deaths of more stars until, at some point, they escaped for a while. “Our solar system captured these elements to make Earth and everything on it,” says Schrijver – including you.

In that sense, we can’t know exactly when we began: it depends how many generations of stars our atoms cycled through. But each of us is at least 4.6 billion years old, the age of the solar system, and perhaps as ancient as the universe’s first stars, which appeared some 13.7 billion years ago, just 100 million years after the big bang. The hydrogen within …