Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Cosmic ray:

This text has been unreferenced on Wikipedia for a very long time. If you can't find a source, be bold and remove it!

"

Cosmic rays kept the level of carbon-14[1] in the atmosphere roughly constant (70 tons) for at least the past 100,000 years,[citation needed] until the beginning of above-ground nuclear weapons testing in the early 1950s. This fact is used in radiocarbon dating.