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  “It never ceases to amaze me that our bodies are constructed of the stuff of stars.” — Stephen Hawking

  “You are stardust.  It is literally the most poetic thing I know about in all of science” — Lawrence Krauss
  “That association–for me–is actually quite enlightening, and ennobling, and enriching.  In fact, it’s almost spiritual.” — Neil Degrasse Tyson


 We are a collection of atoms that understands that it is a collection of atoms…  [We are] the universe knowing that it is the universe.

— Dr. Nina Lanza, How the Universe Works, s04e05, Discovery Communications, 2015

So where do YOU ultimately come from?  Is it too abstract to declare in the first sentence that you came from space?  Yes, I guess it’s a poor way to start; you would argue sensibly that no, you came from the womb and there may even be pictures and video to prove it, to which I would reply… eww, and then this post would prematurely end in awkward silence.  To be clear, I am not disputing that you came from your mother’s womb.  But your mother came from space….  Okay, let me start over:  So everyone had a mother and everyone came from the womb; but take a moment to consider that your body, and the body of the mother who bore you, and hers before her, was built up over 8 or 9 months simply using proteins and minerals already present or ingested during pregnancy by the body that produced you.  In short, you were produced in a secure environment, but your unique cells were assembled from already existing atoms.

I probably don’t have to tell you that you started small; every person on earth spent their first half hour as a single cell, what we refer to as a zygote (see, already you sound like you came from space).  The definition, according to Wikipedia:  “a cell formed when two gamete cells are joined by means of sexual reproduction.  In multicellular organisms, it is the earliest developmental stage of the embryo.”  By the time you were born your body was an amazing construction of 100 trillion cells working in concert.  But every individual cell is finite; about three hundred million cells die every minute — you don’t feel your body slipping away because they are always replaced in kind.  Neil Shubin, from his 2008 book Your Inner Fish:

 Our skin cells, for example, are continually dividing, dying, and being sloughed off.  Yet you are the same individual you were seven years ago, even though virtually every one of your skin cells is now different:  the ones you had back then are dead and gone, replaced by new ones.  Like a river that remains the same despite changes in its course, water content, even size, we remain the same individuals despite the continual turnover of our parts.

— p. 118

It is estimated that we slough off some 8 pounds of cells a year.  Yes, that’s 8 pounds!  By this metric, there is more YOU outside of you, blowing in the wind and gathering as dust in your house, than still an organized part of you.  Even as you reached your teens, by weight, YOU were already the minority of you.  It reminds me of Charlie Brown’s friend, Pigpen, forever sporting a cloud of dust behind him; if we had special glasses and time lapse video, we might all appear like Pigpen, leaving behind a cloud of dead residue.  (Eww… and again awkward silence.)

So a human cell follows a lifespan and then it dies, replicated by another — in fact, every ten years your face has completely regenerated with cells that are clones of their predecessors.  Interestingly, the same is true on the larger, more abstract scale – with the “face of humanity” — which regenerates every hundred years from the clones of its predecessors.

So let’s take a moment to understand the difference between our cells (finite, organic chemistry) and atoms (the cell’s non-living and essentially-eternal constituents).  Here’s a sense of scale:  each of your 100 trillion cells is made up of roughly 100 trillion atoms.  In simple terms, you are to the scale of the cell what the cell is to the atom.  An atom is the smallest constituent of matter that is still an element; the atom is the end of the road.  An atom of gold is a smallest portion of gold you can cut it into; if you were to cut it smaller it would by definition no longer be gold.  Cut it any smaller you’d simply be breaking down the universal parts of an atom (protons, electrons, neutrons), dismantling the hardware, if you will.  Though a cell is much larger in size, the same general principle applies from the inorganic to the organic; a cell is the smallest constituent of you that is still “you.”  If you were to cut a cell any smaller, you’d simply be splitting constituent parts (acids, sugars, water, etc.).

Think of a body as an entire civilization; one human cell then, might be imagined as a city, a well-organized metropolitan layout following a strict master plan (its DNA), which was handed down by the city planner (aka, the parents).  But what is the city made of… bricks, steel, glass, drywall and mortar.  Just as each body is made up of 100 trillion cells, and each individual cell is made up of roughly 100 trillion atoms, think of the atom then as a single grain of sand in the countless bricks or sheets of glass that make the city.  The city is a magnificent collection of structures, but we don’t often consider the fact that each and every grain of sand making up the city existed long BEFORE the city, and will last long AFTER it’s gone.  The grain of sand is re-purposed over millenia.  This distinction made, now consider the untold and unheralded story of the atom, because this is the story of everything.


Code Breaking

Complexity arises out of simplicity.  So much in our universe is just an expression of code combinations.  Our DNA is made up of a base of just four chemical compounds, yet repeated enough times that the result is a staggering diversity.  A mix of just three primary colors results in 64 crayons in the box, and every song ever made has been just a different arrangement of 12 recurring notes. Our alphabet is made up of 26 letters, and from that, not just one, but multiple languages are possible.  Our universe is no different; it is the end result of just 92 basic chemical elements, mixed together in different combinations.  There are only 92 types of naturally occurring atoms in our universe.  Think of our universe as an amazingly flavorful stew made up of just 92 ingredients… and ultimately, 91 of those 92 were made from just the first.

The recipe of our universe, as it turns out, was that big old white poster that hung at the front of your old school classroom.  There sitting atop the old periodic table was that one simple letter “H”, as fundamental, simple and iconic as the big “E” on an eye doctor’s chart.  Made up of just one proton and one electron (hence its atomic number 1), hydrogen is the simplest and most abundant element in the universe and was the first atom to congeal in those first several hundred thousands years after the Big Bang.  Forgive me if I shout this: it is interesting to note that roughly 10% of your body is more than 13 billion years old!  Atoms, like that grain of sand, are simply recycled and re-purposed, and the closest physical property to eternal that exists in our universe.  In the first several million years of the universe the only element was hydrogen — well, technically, hydrogen and a little helium (elements 1 and 2) — and even today our universe remains an overwhelming 98% hydrogen/helium mix; all of the other 90 elements you see on the periodic table make up less than 2%.  Hydrogen is the fuel of our universe.

So let’s all agree hydrogen is basically awesome and awesomely basic (and if you bake it a cake just don’t light the candle).  Here’s the breakdown, and where I always got confused and hung up thinking about this concept as a child:  there was nothing physical that came out of the Big Bang — there were no planets, no asteroids or rock; not even the slightest speck of dust came out of the Big Bang.  (Yes, the Big Bang was dust-free.)  Dust, rocks, asteroids, planets and people all require carbon, and carbon was yet to exist.  Now to be clear, making a universe using only hydrogen and helium would not be unlike trying to form a language using only the first two letters of the alphabet… you’d be hard pressed to produce a single word, much less an entire language.  But just as a language starts with one word, so does a universe start with just one element.  The difference between an empty universe of hydrogen and a universe of planets and buildings and oceans and bumblebees and endless M*A*S*H reruns and YOU reading these words was gravity.  Matter and gravity are a feedback cycle; the more mass an object gains the more gravity it exerts, which in turn attracts more mass to it.  Brought together by this fundamental force of gravity, hydrogen clouds gathered, compressed and lit up into the first generation of big blue hydrogen stars.  It was stars, in one form or another, that ultimately created all the other natural elements that exist today, fused together within the furnaces of their cores.  Stars are the stars of our story.

This process — the creation of heavier elements from lighter elements through fusion — is known as nucleosynthesis.  A process proposed as early as the 1920s during the early days of quantum physics, by 1957 the last details of the amazing story of stellar nucleosynthesis were finally understood.  Imagine two hydrogen atoms thrust together into one… one atom with two protons is by default no longer hydrogen but helium (element #2, with 2 protons and 2 electrons).  Helium can fuse into lithium (element #3, with 3&3) and beryllium (#4, 4&4), or three helium atoms (three #2s) can fuse directly into one carbon (#6) in a neat trick called the triple-alpha process, initiating the “CNO cycle” as carbon fuses into nitrogen (#7) and oxygen (#8).  The process continues up the scale; in essence, one sees the order of creation and the difficulty in creation with the ascending order on the periodic table, with every number representing a new and heavier elemental material than the one before.  Stars are element factories, through escalating pressures creating ever more complex elements right up to the last instant of their existence (to iron #26), and then only in that instant of the violent death/explosion of a star in a supernova/hypernova/neutron star merger does the process overcome the iron barrier to create the even rarer elements… from silver (#47) and gold (#79) and lead (#82) to uranium (#92)… and all the elements the star spent its life and death making are blown out into the universe.


 The Third Star

 The cosmos was originally all hydrogen and helium; heavier elements were made in red giants and in supernovae and then blown off into space, where they were available for subsequent generations of stars and planets.  Our Sun is probably a third generation star.

  Carl Sagan, Cosmos, Ep. 9, PBS, 1980

So stars function as the great seed spores of the universe.  In the early universe stars lived and died alone; there simply couldn’t BE any planets, comets, asteroids or dust because there were no heavy materials.  It was the detonation of these first stars that introduced chemistry into the universe for the first time.  Now instead of just two letters, there was an entire alphabet from which a language could be constructed.  Complexity became possible.  Here’s the takeaway: there had to have been at least two generations of stars living and dying in order to create the rich abundance of heavy materials that make rocks, planets, our earth, the universe we see today, and life like us.  From NASA…

 Our Sun is thought to be a third-generation star and our entire solar system is made of the recycled star stuff of previous star generations.

– NASA (https://solarsystem.nasa.gov/yss/display.cfm?ThemeID=2&Tab=Background)

In the 1950s two broad classifications for stars were created

  • Population I stars, meaning third generation, relatively new and high in metallicity.  Our own sun is a Population I star.
  • Population II stars are the older generation and demonstrate a less metal-rich composition.

In 1980 a third classification was added

  • Population III stars (the first generation) are theoretical and thought to be long extinct, but would have contained no metals at all.

Simply, through the process of stellar nucleosynthesis each star produces within its interior heavier-than-helium elements that in turn are released upon supernova, which enriches the next generation of stars that form from its nebula.  It goes without saying that long before you were here your ancestors were here.  So by applying the same anthropic principle that declares that your grandfather must have existed because you exist, quite simply the only way our sun, with its heavier elements, can exist is because some nearby Population II star (or stars) detonated, creating our higher-metallicized stellar nursery.  The universe existed some 9 billion years before our solar system, but we couldn’t exist without those 9 billion years before us.  “Only Population I objects are expected to harbor planetary systems.” (– http://www.daviddarling.info/encyclopedia/P/PopI.html)

The human body is made up of 65% oxygen atoms, 18% carbon, 10% hydrogen, 3% nitrogen, 1.5% calcium, 1% phosphorous… in short, you are made 100% of atoms, and 100% of those (non-hydrogen) atoms came out of long dead stars… there is simply no other way to generate them.  You are literally stardust.  Every non-hydrogen atom in your body came from a star, but not one came from a star that you see in the sky today.  They — and we — are descended from those generations of stars that died long before us.  The stars that dot the night skies of today are made of the same stuff, our atomic cousins.

 Except for hydrogen and helium, every atom in the sun and the Earth was synthesized in other stars.  The silicon in the rocks, the oxygen in the air, the carbon in our DNA the gold in our banks, the uranium in our arsenals were all made thousands of light-years away and billions of years ago.  Our planet, our society and we ourselves are built of star stuff.

  Carl Sagan, Cosmos, Ep. 9, PBS, 1980

And you might notice the above caveats regarding hydrogen… as pointed out previously the hydrogen atoms are even older!  Your body is a sculpture some 13 billion years in the making, using materials brought together from across vast distances of the universe.  The five most common elements in the universe are hydrogen, helium, oxygen, carbon and nitrogen.  The most common elements in your body are oxygen, carbon, hydrogen and nitrogen; helium aside (which is a noble gas & chemically inert), your body reflects — virtually in kind — the makeup of the universe around you.  The ingredients that result in life are the elements that are most common throughout the universe.

 In order that we might live stars in the billions, tens of billions, hundreds of billions even, have died.  The iron in our blood, the calcium in our bones, the oxygen that fills our lungs each time we take a breath — all were cooked in the furnaces of stars which expired long before the earth was born.

Marcus Chown, The Magic Furnace, p. 211

The chemical elements are a broth made from a soup of accumulated supernova waste.  To consider this notion poetically, the atoms in just the tip of your pinkie could have come from a hundred different stars.  Every rock, every tree, every blade of grass, every bird, every breath of air, everything you see and feel and everyone you’ve ever known in this material universe is made of atoms from an ancient fusion in the belly of a star.  To consider it more mundanely, you and I and everyone you know and everything you see are little more than a waste byproduct of stellar processes… in a very real and literal sense, nuclear waste.  However you tend to see it, we are merely short-term hosts for these atoms, we’re just a temp job; they’ve existed billions of years before us and will outlast us by the same.  To paraphrase Carl Sagan, we are the ashes of hydrogen fusion that have achieved self-awareness.  We are a way for the universe to know itself, if only for a moment, before like a star we release our borrowed atoms back into the universe to be recycled again elsewhere.

 Every living thing is just a temporary home for carbon atoms that existed long before there was life on earth and will exist long after… earth [is] gone.

— Professor Brian Cox, The Wonders of Life, Ep. 3, BBC, 2012

 What’s true is that we are only the temporary custodians of the particles which we are made of.  They will go on to lead a future existence in the enormous universe that made them.

— Stephen Hawking, Into the Universe, Discovery Communications, 2010

Additional Reading:

 Population I, or metal-rich stars, are young stars with the highest metallicity out of all three populations. The Earth’s Sun is an example of a metal-rich star.

 All Population I stars are relatively rich in elements heavier than hydrogen and helium since they formed from clouds of gas and dust which contained the products of nucleosynthesis from previous generations of stars. The presence of heavy elements in protoplanetary disks is believed to be a key factor in the formation of planets, so that only Population I objects are expected to harbor planetary systems.


 The Sun also belongs to the Population I group of stars, which contain relatively large amounts of heavier elements. The first ever stars, made from pure hydrogen and helium are Population III. These exploded as supernovae, producing fusing the lighter elements into heavier and heavier elements. Our Sun, then, contains the metal from previous generations of stars that went supernova.


 Because stars manufacture heavier elements, each generation of new star forms from material previously enriched by previous generation stars and therefore has a higher metallically than the previous generation.
So it’s thought our sun is formed from material already recycled, produced by two previous generations of stars that came before it…. This can be measured by looking at the spectral lines to determine the composition of the star and hence the likely generation it was formed in, the higher the metallically ratio the older the generation of material the star was formed from.

Composition of the sun, listing its metallurgical content:  http://hyperphysics.phy-astr.gsu.edu/hbase/tables/suncomp.html

Breakdown of the process of stellar nucleosynthesis:  Stellar nucleosynthesis – Wikipedia, the free encyclopedia