It’s not “radiation levels” per se. Nuclear bomb testing in the mid 20th century dramatically increased the amount of carbon-14 in the atmosphere, which has sub

It’s not “radiation levels” per se. Nuclear bomb testing in the mid 20th century dramatically increased the amount of carbon-14 in the atmosphere, which has subsequently been gradually declining. https://en.wikipedia.org/wiki/Carbon-14#Origin https://en.wikipedia.org/wiki/Carbon-14#Origin