In this blog post, we explore from a scientific perspective where the atoms that make up the human body come from and what cycle they undergo after death.
“Where do humans come from, and where do they go?” This question has stimulated human curiosity across all eras and places. Since time immemorial, humans have attempted to answer it, and those who offered plausible answers are remembered as great philosophers and thinkers. This question extends beyond the mere issues of human origin and end, leading to a profound exploration of the meaning and purpose of existence. Ultimately, it asks why we are here and what direction our lives should take. The fact that people still ponder this question today shows how difficult it is to find a definitive answer.
What answer would a scientist give? Where did the matter that makes up our bodies originate, and what happens to us after we die? Unlike discussions from philosophical or religious perspectives, science offers us more concrete and clear answers about our material origins and destiny.
Every object we encounter in daily life is composed of atoms. Atoms are unimaginably small particles; the roughly 100 types of atoms existing in nature combine in various ways to form the countless objects of the world. Think of them as nature’s Lego blocks. Atoms consist of a nucleus and electrons orbiting around it. The nucleus itself is made up of protons and neutrons. The number of protons determines the type of atom: an atom with one proton is hydrogen, one with two is helium, and so on. Changing the number of protons changes the element. Atoms of various kinds combine in different ways to form matter, creating the countless beings throughout the universe. Naturally, our bodies are no exception. The human body is composed of a staggering 100 trillion atoms, with diverse atoms like hydrogen, oxygen, carbon, and nitrogen bonding to form even more varied substances. These substances each perform their specific roles within our bodies, enabling us to sustain life.
So, when and where did the atoms that make up our bodies originate? To answer this question, we must look beyond Earth. At the core of stars that shine on their own, like the Sun, temperatures are incredibly hot and pressures are immense. Under these conditions, two atoms can collide, causing their nuclei to fuse into a single, larger atom. This process is called nuclear fusion. Stars shine because the energy released from nuclear fusion is emitted as light. Nuclear fusion is crucial in the history of the universe because initially, only hydrogen existed in our cosmos. All other elements were created through nuclear fusion from hydrogen, the smallest element with just one proton. And the only place in the universe where nuclear fusion occurs is inside stars. Carbon with 6 protons, oxygen with 8, and even iron with 26 protons—all were forged inside stars at some point.
And these newly created elements are scattered throughout the universe when stars explode upon their death. Every atom on Earth (except hydrogen) was created in some distant star long ago and flew into the solar system with that star’s death. For 4.5 billion years, they have circulated through Earth’s air, rocks, plants, and animals, eventually forming our bodies today. The hydrogen or oxygen atoms in our bodies likely came from water we drank weeks ago, while nitrogen came from protein foods like meat or beans. Naturally, our bodies are not the final destination of this vast cycle. The countless carbon dioxide molecules contained in the breath we constantly exhale are made up of carbon and oxygen atoms you once brought into your body from outside. This carbon dioxide may dissolve into the ocean, or it may someday be absorbed by a tree, becoming part of its leaves or branches. Thus, it will begin its endless journey around the entire planet once more.
We often feel human life is finite, but from a scientific perspective, we realize we are part of an eternal cycle. It is said that in five billion years, the Sun will no longer be able to shine. As the Sun meets its end and swells, the Earth’s matter will be unable to withstand it and will be flung far away, scattering haphazardly into the cosmos. The hydrogen that once formed your body may, after an immense span of time, enter a star somewhere far away in the universe and become fuel for nuclear fusion. Perhaps the carbon atom I just exhaled will someday flow into another planet and form the body of a lifeform living there.
The human body originates from other beings and returns to other beings, no different from the other matter that makes up the entire universe. The atoms that make up my body are not mine alone. Countless beings before me held those atoms, and countless beings after me will pass through them. Thinking this way, one can realize that all life on Earth, and indeed the entire universe, is not isolated from one another.
