“The cosmos is within us. We are made of star stuff. We are a way for the universe to know itself.”
Carl Sagan
We, and every other lifeform on Earth, are made of star stuff. The very core elements within our bodies— carbon, hydrogen, oxygen, and nitrogen—were forged within the hearts of stars long lost to our night sky. Spread out through the cosmos through supernova events. The death of stars giving rise to life itself. Stardust. But how? What do we mean when we say those elements were forged within stars? Why not somewhere else, and how would they have ended up not just on earth, but embedded within its very makeup?
The Beginning of the Universe | Hydrogen and Helium
The story of a tray of cookies does not begin with the cookie fully cooked, but with its ingredients, how they were put together, and the conditions under which the cookie came to be. Similarly, the story of life begins not with a first cell, but with the Big Bang, around 13.8 billion years ago. In the universe’s first moments, temperatures were extremely high, allowing only the simplest elements to form. Hydrogen, the lightest and most abundant element in the universe, was the first. Just one of each subatomic particle—an electron, a proton, and one singular neutron. This is indicated on the periodic table with the hydrogens assigned atomic number of 1. Shortly after, helium (atomic number 2) began to form. Together, these two elements make up nearly all the matter in the universe, but they are just the starting point.
As the universe expanded and cooled, gravity pulled hydrogen and helium together into vast clouds. Over millions of years, these clouds formed the first stars. In the cores of these stars, nuclear fusion began—the process that powers stars and creates new elements.
Stars like our Sun spend most of their lives turning hydrogen into helium. When a star runs out of hydrogen, it starts to fuse helium into heavier elements. In stars similar to or larger than our Sun, this process will eventually lead to the creation of carbon. Through something called the triple-alpha process, three helium nuclei combine to form carbon (atomic number 6). Carbon is crucial for life, forming the backbone of complex molecules that make up living organisms.
After carbon, stars can fuse helium (2) and carbon (6) to make oxygen (atomic number 8). Oxygen is vital for life, especially for processes like breathing, and in turn, respiration. In larger stars, this fusion continues, creating even heavier elements.
Nitrogen (atomic number 7) forms in both large and medium-sized stars. During the later stages of a star’s life, carbon and oxygen can capture protons and neutrons, forming nitrogen. Nitrogen is a key component of amino acids, proteins, and DNA, making it essential for life.
Cosmic Explosions
While stars produce many elements, the heaviest ones need even more intense environments. When massive stars reach the end of their lives, they explode in supernovae. These explosions scatter the elements made in the stars’ cores into space, enriching the universe with carbon, oxygen, nitrogen, and many others.
Supernovae act like cosmic forges. The heat and pressure during these explosions create elements heavier than iron, such as gold and uranium. The remains of these stellar deaths—nebulae enriched with heavy elements—become the birthplaces of new stars and planetary systems. In a sense, supernovae are cosmic seed dispersal events, spreading the ingredients of life across the universe.
Our Sun and solar system formed about 4.6 billion years ago from such a post-supernova nebula. This cloud of gas and dust contained the remnants of previous stars, including the carbon, hydrogen, oxygen, and nitrogen necessary for life. As gravity pulled this material together, it formed our Sun, planets, and other celestial bodies.
Earth, made from this star-studded material, is rich in elements forged in ancient stars. The water we drink, the air we breathe, and the molecules that make up our bodies all come from elements that were once at the heart of a star. The question is, if these elements are embedded within the very earth itself, how were the released? How did the combine and recombine to form the various macromolecules necessary for life? That is a topic for the future.
Every atom in our bodies has a history that goes back billions of years. Hydrogen, a remnant of the Big Bang, flows in our veins as part of water. Carbon, created in the cores of ancient stars, forms the backbone of our DNA. Oxygen, born from stellar fusion, helps us breathe. Nitrogen, forged in dying stars, is essential to our genetic code.
We are part of an ancient, ongoing story written in the language of the stars. As we look up at the night sky, we can see echoes of our existence in the twinkling lights of distant stars, knowing that we, too, are made of star stuff.
Thank you for reading part one of a new series I am working on— BIO 101.
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The Wild Life was created in January of 2017 by, me, Devon Bowker after finishing my degree in wildlife biology. It’s been amazing to see how things have changed over the past 7 years, both personally and here. I have tons of ideas and projects in the works and cannot wait to share them with you. Whether you’re a long-time follower or new to The Wild Life, thank you for being here.
