Lightning strikes cause nuclear reactions in the atmosphere

Photonuclear reactions triggered by lightning during a thunderstorm have been directly observed for the first time. Bursts of lightning are known to produce γ rays in the form of photons, and it has long been speculated that these could collide with other atomic nuclei in the atmosphere and result in radioactive decay. For example, when nitrogen-14 or oxygen-16 are hit by high energy photons unstable radioactive isotopes like nitrogen-13 or oxygen-15 are generated, along with neutrons.