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  • Writer's pictureStephen Birchard

“We are Stardust”: How the iron in our blood came from the fiery furnaces of the cosmos.

“We are stardust, we are golden, And we've got to get ourselves back to the garden.”

Woodstock, Joni Mitchell

According to astrophysicists, the elements that make up our bodies, such as the calcium in our bones and the iron in our blood, were formed billions of years ago in distant stars in the universe. It is the same iron that was generated inside stars from the time of the Big Bang, that cataclysmic event that gave birth to all the suns, planets, and moons. As astronomer Carl Sagan said: “We are made of starstuff. The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars.”

Artistic depiction of our solar system.
Figure 1: The solar system

In my mind this is the ultimate reality of how we are connected to nature. The building blocks of our bodies originated somewhere in the heavens, and we share this cosmic history with everything on earth: animals, plants, rocks, and soil. The chemical elements from the universe make up the molecules that comprise everything.

“The Star in You”, an article from the PBS series “Nova” written by Peter Tyson, describes how it all happened. The chemical elements in the periodic table, those substances that cannot be broken down any further through chemical means, were formed via thermonuclear reactions in stars that were contracting due to gravity at the end of their lifespan.

Figure 2: The Periodic Table of Elements, all of which were generated billions of years ago within stars.

One of those elements is iron, chemical symbol "Fe". Iron is at the center of each molecule of hemoglobin in our blood. Hemoglobin is the essential part of blood that carries oxygen from the lungs to the body's tissues. Chlorophyll, a molecule practically identical to hemoglobin, allows conversion of sunlight to energy in plants. At the center of each molecule of chlorophyl is Magnesium, chemical symbol "Mg". Two metals, iron and magnesium, are essential for life on our planet and were produced in the universe billions of years ago.

Figure 3: Note the similarity of these 2 essential molecules of life. Other than their central element (Iron in hemoglobin and Magnesium for chlorophyll) A and B indicate the only differences between them.

When stars burn out and lose their mass, they release into space the elements that have formed inside them. New stars form and go through the same process, called galactic chemical evolution. Our own sun is going through this process right now. It is currently only hot enough to convert hydrogen into helium, a mere 10,000 degrees Fahrenheit. But when it evolves into a red giant on its way to burning out, it will become even hotter; hot enough to generate more chemical elements. But don’t hold your breath; that will not happen for another 5 billion years.

We marvel at the stars in the night sky, but their distance from us makes it hard to imagine we have any physical connection to them. Scientists have now traced the very basic elements in our bodies to those celestial bodies that sparkle above us. Without them and their galactic chemical evolution nothing here on earth, including us, would exist. We are inextricably linked to everything, including celestial bodies that are light years away.

From Carl Sagan’s book Cosmos*: “We have begun to contemplate our origins: starstuff pondering the stars; organized assemblages of ten billion billion billion atoms considering the evolution of atoms; tracing the long journey by which, here at least, consciousness arose.”


* I highly recommend Dr. Sagan’s book. I am re-reading it now for the third time. Although published in the 1980’s, it is as relevant today as it was then. He has a unique gift for describing the universe in an eloquent and captivating manner; combining science, philosophy, and poetry to show us why we should be awestruck whenever we look to the night sky.



Figure Credits

Figure 1: Pablo Carlos Budassi, CC BY-SA 4.0 <>, via Wikimedia Commons

Figure 2: 2012rc, CC BY 3.0 <>, via Wikimedia Commons

Figure 3: Jcauctkting, CC BY-SA 4.0 <>, via Wikimedia Commons

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4 commenti

24 set 2022

This article is truly un-believable, I always used to have knowledge of our bodies coming from stardust, but being truly honest I never knew why. That's why I came here to see how and what fundamentals come into play. I always used to love the thought of originating from the stars and what kind of aspects come into play while this process happens. Thank you so much.

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Stephen Birchard
Stephen Birchard
25 set 2022
Risposta a

Thanks for your comment. It's gratifying to know that others are, like us, awestruck by our connection to the cosmos. When science expands our understanding of the universe, and our place in it, the result is nothing short of magical.

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Russ Crabtree
Russ Crabtree
12 nov 2021

Thank you. I love this reminder!! I just read this week that scientists now believe the universe did not begin to emit its first light until about 380,000 years after the big bang. I try to imagine what it would be like to have been an observer back then...complete darkness...and then, lights coming on like cosmic fireflies. It's just too wonderful to imagine...

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24 set 2022
Risposta a

Ah, thank you for sharing! I never knew this! That is wonderful.

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