Cosmic Ray Spallation

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Carl Sagan famously said that people are starstuff contemplating the stars. His point was that the atoms are not now as they've always been, and that stars are the furnaces that churn the light atoms that emerged from the Big Bang into the heavier stuff that composes the planets and the creatures of Earth. This is how it usually works, but it's not always so. As we've seen before, the whole universe once made heavier atoms like the inside of a star, and some of the matter of our planet is only made when blindingly fast particles from deep space slam into Earth's atmosphere and surface. You can read more about that here:
Cosmic ray spallation

There's a lull in the periodic table of the elements between helium and carbon. Helium was made in tremendous quantities during the Big Bang and by several generations of stars before the solar system came into being, and an efficient process exists in large stars to convert helium into carbon. Lithium, beryllium, and boron, the elements between helium and carbon in atomic weight, don't fit neatly into these standard creation stories, though, and are quickly burned up in stars and converted into more mundane stuff like carbon, oxygen, and neon.

As rare as these elements are, they still clearly exist on Earth. Without lithium batteries, cell phones would still be the size of bricks. Without beryllium, emeralds (beryllium ceramics with a hint of chromium) would be nowhere to be found. Without boron, the green flash of triethylborane igniters (pictured in a SpaceX Falcon 9 test above) would look much more mundane. The reason Earth is graced with their presence is because space is full of violent explosions that create particles that fly through the cosmos at close to the speed of light. When these small nuclei collide with each other, or with the atoms in planets and interstellar dust, they blast the atoms apart, and small fragments, the stuff of a boron atom, say, are left behind. It doesn't happen often enough to compete with the output of the stars, but it does happen often enough that emeralds aren't as rare as platinum, at least in the Earth's crust.

Not everything made by cosmic ray spallation is built to last. A small amount of radioactive carbon is constantly coming into being in the upper atmosphere when neutrons generated by cosmic ray collisions knock protons out of the nitrogen atoms that surround Earth. The neutrons take the protons' places, and the nitrogen is transmuted into carbon-14, which is chemically identical to the ordinary carbon-12 that makes everything from proteins to airplanes to diamonds, but radioactively decays with a half-life of about 5,700 years. To put that in perspective, the pyramids at Giza have about a millennium to go before they've been around for a carbon-14 half-life.

About one in a trillion carbon atoms on Earth is radioactive, and since the supply is constantly being replenished living things have the same amount of carbon-14 in their tissues as long as they keep breathing and eating. Once the mortal coil is shuffled off, though, the carbon decays without replacement, and by measuring the ratio of radioactive to ordinary carbon the time of death can be established with decent precision. Radiocarbon dating, as it's known, has become a staple of archaeology since the physics here was first figured out. Several other radioactive isotopes are also made by cosmic ray spallation, and provide a range of dating scales for similar work. As odd as it sounds, the afterglow of far off worlds gives us some of the best clues about how things work here at home.