In her classic song, Woodstock, Joni Mitchell ended with the chorus:

We are stardust
Billion-year-old carbon
We are golden
Caught in the devil’s bargain
And we’ve got to get ourselves
Back to the garden

Which most people assume is merely poetic licence. Well, Joni wasn’t wrong: we – and every living thing on our planet – are made of stardust. As we learn at Physics Central:

If we know how many hydrogen atoms are in our body, then we can say that the rest is stardust. Our body is composed of roughly 7×1027 atoms. That is a lot of atoms! Try writing that number out on a piece of paper: 7 with 27 zeros behind it. We say roughly because if you pluck a hair or pick your nose there might be slightly less. Now it turns out that of those billion billion billion atoms, 4.2×1027 of them are hydrogen. Remember that hydrogen is bigbang dust and not stardust. This leaves 2.8×1027 atoms of stardust. Thus the amount of stardust atoms in our body is 40%.

Since stardust atoms are the heavier elements, the percentage of star mass in our body is much more impressive. Most of the hydrogen in our body floats around in the form of water. The human body is about 60% water and hydrogen only accounts for 11% of that water mass. Even though water consists of two hydrogen atoms for every oxygen, hydrogen has much less mass. We can conclude that 93% of the mass in our body is stardust. Just think, long ago someone may have wished upon a star that you are made of.

Mitchell’s theme was picked up by the late cosmologist, Carl Sagan, in his hit TV show, Cosmos. Live Science tells us:

In the early 1980s, astronomer Carl Sagan hosted and narrated a 13-part television series called “Cosmos” that aired on PBS. On the show, Sagan thoroughly explained many science-related topics, including Earth’s history, evolution, the origin of life and the solar system.

Since stardust atoms are the heavier elements, the percentage of star mass in our body is much more impressive. Most of the hydrogen in our body floats around in the form of water. The human body is about 60% water and hydrogen only accounts for 11% of that water mass. Even though water consists of two hydrogen atoms for every oxygen, hydrogen has much less mass. We can conclude that 93% of the mass in our body is stardust. Just think, long ago someone may have wished upon a star that you are made of.

“We are a way for the universe to know itself. Some part of our being knows this is where we came from. We long to return. And we can, because the cosmos is also within us. We’re made of star stuff,” Sagan famously stated in one episode.

His statement sums up the fact that the carbon, nitrogen and oxygen atoms in our bodies, as well as atoms of all other heavy elements, were created in previous generations of stars over 4.5 billion years ago. Because humans and every other animal as well as most of the matter on Earth contain these elements, we are literally made of star stuff, said Chris Impey, professor of astronomy at the University of Arizona.

“All organic matter containing carbon was produced originally in stars,” Impey told Life’s Little Mysteries. “The universe was originally hydrogen and helium, the carbon was made subsequently, over billions of years.”

So how did all this stardust get into out bodies? Supernovae, spewing heavy material into the vastness of space, scattering atoms and molecules at near lightspeed. Our “Garden of Eden” was the nuclear furnace of an exploding star.

We are made of the material created 13-plus billion years ago, We are, as Mitchell sang, stardust. Recycled and reused, but the stuff of the cosmos nonetheless. *

And we’re also built of viral genes, a product of the evolution of life, of the co-evolution of life and that strange creature, the virus. Viruses have helped shape us, and our adaptations to the environment. That’s the premise of Frank Ryan’s latest book, Virolution.**

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