When you look at your hands or feel your heartbeat, you’re experiencing something that connects you to the deepest mysteries of the universe. Most of the elements that make up the human body were formed in stars. This isn’t just poetic language – it’s hard science that reveals how our bodies are literally assembled from cosmic material that traveled through space for billions of years. Every atom of carbon in your cells, the oxygen you breathe, and even the iron coursing through your blood was once forged in the heart of an ancient star. When those stars exploded as supernovae, they scattered their elements across the cosmos, seeding future solar systems—including our own. Over billions of years, that stardust clumped together to form planets, oceans, and eventually, life itself. In a very real sense, we are walking pieces of the universe given form, carrying the history of the cosmos within us. It’s a reminder that our story isn’t just human—it’s cosmic.
The Big Bang’s Limited Menu
We think that the universe began about 13.8 billion years ago with the Big Bang. At that point, only the lightest elements, such as hydrogen, helium and minuscule amounts of lithium existed. Picture the universe as a cosmic kitchen that started with only three ingredients. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium.
These first elements were like raw materials waiting for a more sophisticated factory. The Big Bang gave us the foundation, but everything else we know and love – the carbon in our DNA, the calcium in our bones, the oxygen we breathe – had to be manufactured somewhere else entirely. That somewhere was the fiery hearts of stars.
Stars as Cosmic Element Factories
The first generation of stars formed as lumps of gas drew together and began to combust. The next generation of seeded stars were then able to produce other, heavier elements such as carbon, magnesium and nearly every element in the periodic table. Think of stars like massive pressure cookers operating at unimaginable temperatures. There’s so much heat and pressure in a star’s core that they can fuse atoms together, forming new elements.
Stars are like big chemical element factories! Even our Sun is currently making new elements inside of it. The process works through nuclear fusion, where lighter elements crash together with such force that they stick, creating heavier ones. It’s like cosmic alchemy, turning the simplest ingredients into increasingly complex materials.
The Journey From Hydrogen to Heavier Elements
Hydrogen fusion (nuclear fusion of four protons to form a helium-4 nucleus) is the dominant process that generates energy in the cores of main-sequence stars. This is where the cosmic assembly line begins. Stars start by fusing hydrogen into helium, releasing enormous amounts of energy in the process. The overall process of stellar nucleosynthesis can be characterized by three stages: Hydrogen Burning: The principal reaction in this stage is the fusion of hydrogen into helium, mainly through the proton-proton chain or the CNO cycle. Helium Burning: Once the hydrogen is exhausted, stars fuse helium into carbon and oxygen in their cores. Advanced Stages: In more massive stars, subsequent reactions lead to the formation of elements like neon, silicon, and eventually iron.
As stars age, they become like master chefs working with increasingly complex recipes. They take the helium they’ve created and fuse it into carbon and oxygen. In the most massive stars, this process continues up the periodic table, creating silicon, sulfur, and eventually iron. However, there’s a cosmic speed limit – stellar burning phases only lead to the production of nuclei up to Fe.
When Stars Die Spectacularly
Stars that go supernova – meaning they explode powerfully – are responsible for creating many of the elements of the periodic table, including those that make up the human body. Our planetary scientist, Dr Ashley King explains how, because of this spectacular phenomenon, we might actually be made of stardust. When massive stars reach the end of their lives, they don’t simply fade away – they explode in supernovae, the most dramatic events in the universe.
Supernova explosions create such intense conditions that even more elements can form. The oxygen we breathe and essential minerals like magnesium and potassium are flung into space by these supernovas. These explosions are so violent that they can create elements heavier than iron in seconds, elements that took the star millions of years to build up to iron. It’s during these cosmic catastrophes that many of the ingredients essential for life are forged and scattered across space.
The Special Case of Iron in Your Blood
Any element in your body that’s heavier than iron has travelled through at least one supernova. The iron flowing through your bloodstream right now has a particularly dramatic origin story. Every drop of blood in your body contains iron: element number 26. But iron isn’t made in small stars. It’s made in death. Specifically, in the explosive collapse of a supernova. That means the hemoglobin flowing through your veins was born in a star’s final scream.
This kind of explosion creates calcium – the mineral we need most in our bodies – and trace minerals that we only need a little of, like zinc and manganese. It also produces iron, which is found in our blood and also makes up the bulk of our planet’s mass! Your bones, built from calcium, and your blood, rich with iron, both carry the signature of stellar violence that occurred billions of years ago.
The Stellar Recipe for Life
The crucial elements for life on Earth, often called the building blocks of life, can be abbreviated as CHNOPS: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. The six most common elements of life on Earth (including more than 97 percent of the mass of a human body) are carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus. When scientists break down what we’re made of, the numbers are staggering. When you break down the biological components of the human body, we are composed of 65% Oxygen, 18.5% Carbon, 9.5% Hydrogen, 3.2% Nitrogen, 1.5% Calcium, 1% Phosphorus, 0.4% Potassium, 0.3% Sulphur, 0.2% Sodium, 0.2% Chlorine and 0.1% Magnesium.
Our DNA is made up of carbon, hydrogen, oxygen, nitrogen, and phosphorus. All those elements (except hydrogen, which has existed since shortly after the big bang) are made by stars and released into the cosmos when the stars die. It’s remarkable to think that the very blueprint of life, encoded in DNA, is constructed from stellar debris. We are literally walking libraries of cosmic history.
From Stardust to Solar Systems
The enriched material ejected by stellar winds and supernova explosions becomes parts of vast interstellar clouds. The Sun formed within such a cloud, where some of the heavy elements condensed to form Earth. After stars die and scatter their elemental gifts across space, these materials don’t just drift aimlessly. They become part of massive gas clouds that eventually collapse under their own gravity to form new stars and planetary systems.
The elements that were created within the cores of the first stars were ejected into space where they intermingled with the surrounding interstellar medium. This medium – the gas and dust between the stars – provides the raw material for the formation of new generations of stars. Eventually, these elements became incorporated into large clouds of gas and dust that condensed and formed protostars. Our solar system formed from one such enriched cloud roughly 4.6 billion years ago, inheriting the stellar legacy of countless previous generations of stars.
The Remarkable Percentage of Stardust in You
It’s true that: about 86 per cent of our mass is “stardust”; almost certainly we each carry at least a few million atoms of gold inside us; and yes, the carbon atoms we carry are mostly many billions of years old. This isn’t just a metaphorical connection – when scientists calculate the actual percentages, the numbers are breathtaking. A 2017 study from the University of California, Santa Cruz, found that humans and our galaxy have 97% of the same kinds of atoms.
The hydrogen in your body tells a different story, though. About 8kg (10 per cent) of our body weight is hydrogen atoms that go back practically all the way to the Big Bang. So you’re a living combination of the universe’s earliest moments and billions of years of stellar evolution. The hydrogen connects you to the Big Bang, while everything else connects you to generations of stars that lived and died before our Sun was even born.
How Stardust Actually Reaches Your Body
The journey from stellar death to human life isn’t direct – it’s more like a cosmic relay race spanning billions of years. “It’s very likely that there are a whole bunch of different stars that have contributed the elements we see in our own solar system, our planet and those found within you”, explains Ashley. “It’s totally 100% true – nearly all the elements in the human body were made in a star and many have come through several supernovas.”
Nearly all of the exact same elements can be found in the human body, and many have transited through several supernovas. You can bet that any element in your body heavier than iron has transited through at least one supernova. Everything you see and touch – even the plants and animals – all of the natural elements in this entire Universe were formed from these nuclear reactions in stars. The calcium in your morning glass of milk, the carbon in your sandwich, the oxygen you breathe – all of it was forged in stellar furnaces and delivered to Earth through cosmic processes operating over unimaginable timescales.
The reality is both humbling and magnificent – we’re not separate from the cosmos but intimately connected to its grandest processes. Every atom in your body, except for hydrogen, was manufactured in the heart of a dying star and hurled across the galaxy to eventually become part of you. What seems like an ordinary day is actually a continuation of an extraordinary cosmic story that began with the first stars and continues through every breath you take.
Jan loves Wildlife and Animals and is one of the founders of Animals Around The Globe. He holds an MSc in Finance & Economics and is a passionate PADI Open Water Diver. His favorite animals are Mountain Gorillas, Tigers, and Great White Sharks. He lived in South Africa, Germany, the USA, Ireland, Italy, China, and Australia. Before AATG, Jan worked for Google, Axel Springer, BMW and others.
