Next time your birthday rolls around and you start to feel old, just put everything in perspective. You may be a few decades old, but there is not a single atom in your body that is under 5 billion years old! There can’t be, it’s simple physics.
You are connected to the cosmos in an intimate way, and your atoms have been around for billions of years, changing their form until five billion years ago they came together in the current form they have and they haven’t changed since then, and they’re in your body.
— Physicist Lawrence Krauss, Lecture, Cosmic Connections, 2011
Our solar system is a construction of materials from previous stars, and as our solar system is under five billion years old, there are few elements present today on the earth that could be any younger than five billion years. Consider for a moment just one single atom of iron coursing through your blood today. That iron atom is a veteran of a star that exploded some four-and-a-half to six billion years ago and was drawn into the solar system when our solar neighborhood was a nebula cloud. As Carl Sagan once poetically noted of nebulae: “Stars are born in batches.”
Later, they wander out of their nursery to pursue their destiny in the Milky Way. Adolescent stars, like the Pleiades are still surrounded by gas and dust. Eventually, they journey far from home. Somewhere there are stars formed from the same cloud complex as our Sun 5 billion years ago. But we do not know which stars they are. The siblings of the sun may, for all we know, be on the other side of the galaxy.
— Cosmos, Ep. 9, PBS, 1980
So stars travel, pulled and drawn by the gravitational currents of the galaxy like something adrift on the ocean, and just like your five or six billion year-old iron atom. Let’s give our iron atom a name. Iron Man. Wait, what… too much? Okay, let’s call it Tony (yes, I’m retaining the Iron Man theme). Tony came out of that last star five or six billion years ago and ended up in the ingredient-broth of our solar system. But how did Tony get there in the first place? Let’s imagine a history for our favorite iron atom.
- Thirteen billion years ago (“hydrogen-Tony”)…
The atom that will someday become our Tony is a simple hydrogen atom (element #1), swirling through the gravitational eddies of the early universe. Suppose our hydrogen atom (let’s call it “hydrogen-Tony”) is swept into the currents of an early star, one of the short-lived “mega stars” that kicked off the early universe’s stellar process. In this case it fuses into helium (#2), alternates into an unstable isotope of beryllium (#4) several times but is never able to overcome the beryllium barrier and decays back into helium. The star blows up after ten million years and “helium-Tony” finds itself, along with some of its neighboring material, amalgamated into a second star. This one maybe lasts about 100 million years, during this time our “helium-Tony” hits the helium lottery, crosses the beryllium border and is ejected as a carbon atom (#6).
- Twelve billion years ago (“carbon-Tony”)…
Our “carbon-Tony” languidly falls into an accretion disc of a third star, where it resides around the periphery for 2 billion years and is ejected an oxygen atom (#8).
- Ten billion years ago (“oxygen-Tony”)…
Having escaped the fusion process of three stars relatively unscathed, let’s hammer Tony with this fourth star. Over the four billion year life of this star “oxygen-Tony” fuses into silicon (#14), then up the helium-4 scale to sulfur (#16), argon (#18), etc., before ending the star’s life as iron (#26), resulting in the Tony we know and love today.
- Six billion years ago to the present day (our “iron-Tony”)…
In our simulation, by now our little friend has played a role in four different stars, been altered in chemistry by each one (and as iron, even contributed to the death of the fourth star) before becoming a part of our solar system, our planet, our biosphere — and for a few months or years — your body. Go, Tony!
This is an amazing journey, and I don’t mean to immediately undermine it. But if we’re going to truly consider this atom’s origins, here’s the realization that will make your jaw drop….
There’s no single beginning to an iron atom… Its Atomic Number is 26, after all. It had no less than 26 different origins. Iron Man, indeed!
So the above reconstruction considers just one lineage of Tony, but there are 25 other “hydrogen-Tonys” — no fewer than 25 other ways this history had to do down — in order to result in an “iron-Tony.” And this is the threshold at which it becomes rather convoluted, like a family tree. Much as you are derived from the merging of two parents, four grandparents and eight great grandparents, any iron nucleus ultimately traces its heritage back to (at least) 26 hydrogen ancestors. Following any one line is like tracing the ancestry of your surname, but there are at least 25 other equally valid branches on this family tree that resulted in “iron-Tony” today, and each traveled its own road and had its own backstory before the paths eventually converged with the current Tony. In other words, instead of four stars, the collective nucleus of Tony could have potentially played a role in as many as 8, 10 or 12 stars… or more. As Lawrence Krauss observed during the lecture referenced above, “Every atom in your body has experienced — maybe more than once — the most violent explosion in the universe.” It’s the “maybe more than once” that I want to emphasize here…. It’s not just the matter of every atom in your body coming from a star, nor the idea that the atoms came from many different stars, but the fact that any ONE atom in your body could have come from MULTIPLE stars. Any single atom in your body — by itself — can represent an alchemy of a myriad of stars, and that bigger picture… almost too big for our comprehension… I kinda think that’s amazing.