There’s an old joke that the astronomer’s periodic table consists of three elements: hydrogen, helium, and metal. It’s a nice joke, but when you understand how little of matter in the universe is “metal”, you can understand why astronomers focus on hydrogen and helium.
Over the past two centuries, we have gained a much better understanding of the atomic elements and how they have formed. One of the things we have learned is that we—and every other living thing on Earth—are made up mostly of four elements. These four atomic elements are oxygen, carbon, hydrogen, and nitrogen. Together they make up about 96% of our bodies.
There’s an old joke that says that the astrophysics periodic table consists of three things: hydrogen, helium and metal. The reason for this is that hydrogen and helium make up about 98% of the atoms in universe.
The atoms in our body appear in about same relative abundance as they do in the solar system.
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