Geomagnetic storms

These are powerful solar eruptions that produce high amounts of cosmic rays in Earth's upper atmosphere, which in turn produce carbon-14, a radioactive isotope of carbon.

The Carrington Event of 1859 is the largest recorded account of a geomagnetic storm, but it is not an isolated event. Recordings of these storms date back to the early 19th century, and an even more massive event is known as the Miyake Event, which occurred around A.D. 774.