I’m in a Carl Sagan state of mind tonight. No, I’m not channeling for Carl. Nobody could do that. But, I was thinking about some of his most famous phrases (and no, NOT “billions and billions”—that was a Johnny Carson schtick). The one that always seemed most evocative to me was “We are, as I like to say, starstuff.”
It seems like a strange thing, to think about coming from a star. But everything on Earth has atoms that were made inside a star. Look at your hand. It has flesh on its bones. Hard to imagine that flesh coming from the hot interior of a star. No, the flesh and bones didn’t. But the stuff that made them up did.

Your hand has atoms of carbon in it. Carbon exists in molecules that bond with other elements to make proteins, nucleic acids, enzymes, carbohydrates, and fats—all things we KNOW make up biological life. Carbon is made in the interiors of stars. Your hand also has calcium in its bones. That, too, came from a star. Heck, our own Sun has calcium in its atmosphere. And, there’s iron in the blood coursing through your veins. The iron atoms came from an ancient supernova explosion that occurred long before the Sun formed.

How do we know all this? The lives of stars are fairly well-understood in general (although many details are still being figured out). But, we do know that stars contain nuclear furnaces deep in their cores. Those nuclear “engines” fuse atoms together. Let’s take the Sun, since it’s the closest star we know of. It started its life fusing hydrogen into helium at its core. Now, the hydrogen was created in the Big Bang, so you’d expect to see plenty of that in the Sun. It gets fused into helium. And it goes from there, atoms getting smacked together to make heavier and heavier elements: carbon, oxygen, silicon and so on. As the Sun (like many stars) lives its live, it makes elements and it sends them out into space through the solar wind.

But, the good stuff happens when stars die. They exhale their outer layers, which contain healthy amounts of the elements they’ve made, into surrounding space. A star like the Sun will swell to become a red giant star, eventually sending much of its mass out to space. That includes oxygen, nitrogen, calcium, and carbon.

If a star is really huge, it will explode in a supernova. The debris of the star, its atmosphere and the elements it has been making—including iron—rushes out to space. A supernova explosion is also the cauldron of creation for elements such as cobalt, uranium, copper, mercury, gold, iodine, and lead.

All stars enrich their immediate neighorhoods with the elements they make. Then, it’s only a matter of time before those elements find their way into new generations of stars. Our own Sun was made from elements that were, themselves, created in far older stars that died and sent their elements into space. Some 5 billion years ago, a cloud of gas and dust enriched by elements from other stars coalesced to form our Sun. And, our planets formed in that cloud, from elements that—you guessed it—came from other stars. And, the elements needed for life (the carbon, oxygen, nitrogen, and iron, just happened to be along for the ride. And voila, after millions and billions of years of planetary formation and evolution, chemical reactions, and biological evolution, here we are—the end products of processes that used star stuff to create planets and favorable conditions for life to form.

So, in a sense, it’s really no surprise that we look to the stars to understand our place in the universe. Somehow we know from where we came, and I think that’s pretty elegant, indeed.