In our universe there are a limited number of ways to create atoms, and each of them are momentous cosmic events that predate the Earth.
Considering how they make up everything around us (including our own bodies) it’s pretty interesting to think about how the atoms that are us once came from places like the center of a star.
The first thing to know is that our Sun is a ‘third generation’ star. It and its planets (including the Earth) formed from the remnants of two earlier generations of stars. They played a crucial role in forming the atoms around us.
But the story of all atoms starts with hydrogen or helium that formed just minutes after the Big Bang. The early universe was full of searing heat and pressure, where trillions of free-floating protons and neutrons fused together to form hydrogen and helium atoms. As the universe cooled over the next few million years, they formed enormous gas clouds, from which came galaxies and the first stars.
Even now, billions of years after the Big Bang, most of the matter in the universe is that original hydrogen and helium.
Most of the original hydrogen and helium from the Big Bang still remains. As time goes on, more will be converted to other elements. Image source: Wikipedia, Abundance of the chemical elements
Hydrogen and helium are like building blocks. These two elements, combined and rearranged, have formed every other element from oxygen to uranium. Each one has a slightly different origin story. The creation of these elements is called ‘nucleosynthesis’.
Stars are always involved in nucleosynthesis. They form within clouds of gas and dust in space, where gravity pulls the cloud into a dense ball. They are ‘born’ when this ball reaches a certain mass.
Stars are usually responsible for the creation of new elements
When its internal pressure becomes strong enough to fuse atoms like hydrogen and helium together, the star ignites. This gives off heat, light, and pressure, and produces other elements like iron, nitrogen, and oxygen as incidental waste.
After billions of years they will run out of hydrogen and helium, and the waste elements build up. What happens next depends on how massive the star is.
Dying and exploding stars
Stars with 8x the mass of our Sun and smaller are considered to be ‘low mass’ stars. When they die they expel their outer layers of gas at a few kilometers per second in an explosion called a ‘planetary nebulae’. The blast seeds the surrounding stars with lithium, carbon, nitrogen, and other elements in smaller amounts. At least 21% of the atoms in our bodies were created in this way.
The core of the star lives on at the center of the explosion. It continues to shine despite having shed much of its mass, though it’s small and not very bright. We call these stars ‘white dwarves’.
Stars with more than 8x the mass of the Sun are considered ‘massive’ stars. They tend to blow up entirely in a titanic explosion called a ‘supernova’. A supernova is one of the most immense and powerful phenomena in the universe. If the Sun went supernova, it would be 1,000,000,000 times brighter than a hydrogen bomb pressed against your eyeball.
Supernovae are visible across the entire galaxy and show up every couple thousand years as a temporary ‘extra’ star in the night sky. The contents of the star are expelled into the universe, and the force of the blast itself fuses together the atoms of many kinds of elements. Supernovae give us oxygen, sodium, neon, aluminium, and tons more elements. At least 65% of the atoms in our bodies originate in a supernova.
They leave behind a tiny ultra-dense core called a ‘neutron star’, compressed by the force of the explosion.
The ‘crab nebula’ is a supernova remnant of a star. At it’s center will be a neutron star.
Exploding white dwarves
Many star systems contain two or more stars closely orbiting each other, in addition to their planets and asteroids. These are called ‘binary’ star systems, and if one star is a low mass star, it can create a special type of supernova explosion.
When the low mass star dies and becomes a white dwarf, it can steal mass from its companion star. If it grows large enough (past the mass of 1.4x our Sun) it will explode all over again in a ‘Type Ia supernova’. This is a unique environment that creates titanium, manganese, nickel, and zinc.
Merging neutron stars
If two companion stars are both massive stars, when they collapse into neutron stars they may collide. They will be crushed together into an even bigger neutron star, and sometimes into a black hole.
When this happens spectacularly intense conditions are produced. A magnetic field trillions of times stronger than the Earth’s is created in two to three milliseconds, the gravitational pull is enormous, and a slew of rare elements are fused in the surrounding gas like uranium, plutonium, and gold. More than 90% of all gold was produced through this incredible event.
Cosmic ray fission
Cosmic rays are the super intense radiation that is blasted into space from supernovae and merging neutron stars. They are gamma rays, the most intense form of electromagnetic radiation.
They are highly energetic and fly through space at the speed of light. If they encounter something like a dusty cloud of carbon, nitrogen, or oxygen, they will collide with their atoms and cleave some of them in two. From these collisions, we get beryllium, boron, and some lithium.
Some elements (especially the really big ones) are too unstable to last long in nature. Over periods of time from seconds to millions of years, they decay into smaller elements and radiation. We’ve created a few elements like this, sometimes on purpose and sometimes as waste products of nuclear bombs, nuclear energy, and particle accelerators.
These elements include technetium, used in diagnosing bone cancer, and californium, used in nuclear reactors. Some of these synthetic elements will last for millions of years, and are almost guaranteed to be the final artifacts of human civilisation.
How they got to Earth
The Sun and the planets (and ourselves) were born out of the supernova remnant of an earlier star. We formed in just the right place where there was a mix of all the elements. The Sun’s gravity pulled them together out of the supernova dust cloud to form the solar system.
On one of those planets, a special type of chemistry called life discovered how to repurpose them. Calcium turned into bones, carbon into carbohydrates, and nitrogen into amino acids. Carl Sagan wrote in his book Cosmos:
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. We are made of starstuff.
Image source: Wikimedia commons, Elements of the Human Body