Iron is all around us. By mass, it’s the most common element in our entire planet. It makes up most of the core and a good bit of the crust. It even gives our blood its red color. And every bit of it was created inside stars.

All stars “fuse” together lightweight elements to make heavier ones. Right now, the Sun is fusing hydrogen, the lightest element of all, to make helium.

Stars like the Sun eventually make a few other elements, such as carbon and oxygen. But most of the elements beyond those are made inside much more massive stars, where temperatures are hundreds of millions of degrees higher. The fusion reactions produce energy, which makes the star shine and keeps it from collapsing under its own gravitational pull.

At the end of this chain of reactions is nickel-56, a radioactive element that decays to make iron. The iron can’t fuse to create heavier elements, so fusion stops. Without those reactions, the star’s core collapses. The layers around the core fall inward, then rebound in a titanic explosion — a supernova.

The explosion blasts many of the elements created inside the star into space. Over time, some of these elements — along with some even heavier ones created in the fury of the supernova — are incorporated into new stars and planets. So the iron that’s such a vital ingredient in our world and in our bodies was forged billions of years ago — in the hearts of stars.

Script by Damond Benningfield

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