Cosmic rays are also responsible for the continuous production of a number of unstable isotopes in the Earth 's atmosphere , such as carbon-14 , via the reaction : Cosmic rays kept the level of carbon-14 in the atmosphere roughly constant ( 70 tons ) for at least the past 100,000 years , until the beginning of above-ground nuclear weapons testing in the early 1950s .
Cosmic rays kept the level of carbon-14 in the atmosphere roughly constant ( 70 tons ) for at least the past 100,000 years , until the beginning of above-ground nuclear weapons testing in the early 1950s .