“We are made of star stuff.”
― Carl Sagan, Cosmos
Who are we, really?
We humans are composed mostly of “organic matter.” Roughly 96% of the mass of the human body is made up of just four elements: oxygen, carbon, hydrogen and nitrogen.
In this essay, we will take a brief tour of where (and when) these elements came from.
And the next time you, or I, feel small and worthless, maybe we can look up, look down, look around – and remember our common heritage, which is nothing less than awesome!
Hydrogen: the oldest atom in the Universe
Hold on… breathe… if you haven’t heard of this before, it will take your breath away! The nuclei of the hydrogen atoms in our body – as you read this line – were formed when our universe was approximately 3 minutes old (yes, you read it correctly). Granted, this was not yet a hydrogen atom, because the temperatures of the nascent universe was still too hot to allow an electron to be recruited to form an electroneutral atom. That happened around 377,000 years later!
Just to put it in perspective… Our universe is currently about 13.8 billion years old. Our solar system, including our sun and our earth, is about 4.5 billion years old. That means that our planetary home wouldn’t even exist for 9.3 billion years after the hydrogens in our bodies were already created! I have created a graph to bring this point home more visually.
Interestingly, even today, about 90% of the universe is still hydrogen!
Note that about 60% of the adult human body weight comes from water. Water itself is composed of two atoms – hydrogen and oxygen.
Now on to carbon, nitrogen and oxygen
At the time hydrogen atom was being created, another atom was also being produced – helium (along with small amounts of lithium and beryllium). These are the smallest atoms in the periodic table, which organizes atoms based on their atomic number (number of protons in their nuclei). Smaller an atom, the easier it is to be formed. Hydrogen is the smallest atom, with an atomic number 1, followed by helium, lithium and beryllium (atomic number 2 - 4).
As the universe cooled further, the atoms left over by the big bang were gravitationally attracted to one another and condensed into massive clouds. The gravitational pressure on the centers of these clouds heated them to temperatures of millions of degrees. This led to the fusion of hydrogen into helium. Thus, stars were born.
These early stars were very massive (several-fold larger than our sun). Due to large masses and dense cores, they were able to continue the fusion reactions to form increasingly larger atoms, namely carbon, nitrogen and oxygen (the so-called CNO cycle). Toward the end of their lives, they produced even larger atoms – all the way up to iron (Fe, atomic number 26). Eventually these early stars died in massive explosions called supernovae – which spewed huge clouds of these atoms. These gas and dust remnants in time formed new stars, which fused more atoms, until they too died in supernova explosions.
Humans as custodians of an ancient heritage
As discussed above, our solar system started its life approximately 4.5 billion years ago as a cluster of gas and dust that was enriched in the materials of life – hydrogen, carbon, nitrogen and oxygen - which were formed in the bellies of generations of older stars.
In other words, of the 96% of our constituent atoms, 9.5% (hydrogen) is 13.7 billion years old (almost as old as the universe itself), and the rest (carbon, nitrogen and oxygen) are at least 4.5 billion years old (and likely older)!
Humans as shepherds of clay
It has been said that poets intuit truths that science arrives at via a different path! Very often, they find a deep resonance. Below is such an example.
The Celtic poet, philosopher and mystic, John O’Donohue, has a beautiful phrase to describe us humans. He calls us “clay shapes,” and even more importantly, “shepherds of clay!”
Here are a few quotes from his incomparable book, Anam Cara, where he lays out our heritage in these terms:
“Humans are new here. Above us, the galaxies dance out toward infinity. Under our feet is ancient earth. We are beautifully molded from this clay.”
“Your body is as ancient as the clay of the universe from which it is made; and your feet on the ground are a constant connection with the earth. Your feet bring your private clay in touch with the ancient, mother clay from which you first emerged.”
“In your clay body, things are coming to expression and to light that were never known before, presences that never came to light or shape in any other individual. To paraphrase Heidegger, who said, “Man is a shepherd of being,” we could say, “Man is a shepherd of clay.” You represent an unknown world that begs you to bring it to voice. Often the joy you feel does not belong to your individual biography but to the clay out of which you are formed. At other times, you will find sorrow moving through you, like a dark mist over a landscape. This sorrow is dark enough to paralyze you. It is a mistake to interfere with this movement of feeling. It is more appropriate to recognize that this emotion belongs more to your clay than to your mind. It is wise to let this weather of feeling pass; it is on its way elsewhere. We so easily forget that our clay has a memory that preceded our minds, a life of its own before it took its present form. Regardless of how modern we seem, we still remain ancient, sisters and brothers of the one clay. In each of us a different part of the mystery becomes luminous. To truly be and become yourself, you need the ancient radiance of others.”