Weekend Edition Sunday, November 16, 2008 -

Back in the 1950s, the Americans, the British, the French and the Russians tried to impress each other by "testing" atomic weapons. This involved blowing up multi-megaton bombs in the air in remote places, but the explosions didn't stay local.

A Couple Of Extra Neutrons...

Each atomic blast released lots of neutrons into the atmosphere, many of which slammed into carbon atoms floating by with the result that lots of carbon atoms gained a couple of extra neutrons. If you remember your Periodic Table of Elements, carbon ordinarily carries 12 protons and neutrons. Add a couple of extra neutrons, and the 12 becomes 14. Which means during the 1950's the world got a boost of carbon-14 atoms.

There was, says Professor Nadlini Nadkarni, an ecologist at Evergreen State College in Washington, "a tremendous spike of carbon-14 — actually 100 percent more carbon-14 coming into the atmosphere than what we'd had previous to those [atom bomb] tests."

Leaving The Neighborhood

Those clouds of carbon-14 atoms didn't stay at the bomb sites. "This cloud of carbon-14 went round and round and round the Earth and was persistent for quite a while," says Professor Nadkarni.

When President Kennedy signed a test ban treaty with the Russians in the early 1960s, nations stopped blowing up bombs above ground and the population of carbon-14 in the atmosphere went down, but, from around 1954 to around 1963, trees all over the world sucked in extra dollops of carbon-14.

Trees don't know the difference between regular carbon and carbon-14. They just breathe in carbon dioxide and use the sunshine to turn that CO2 into plant food stored in their trunks, so that if you look inside a tree, any tree, you can measure the carbon within. And here comes the big surprise.

For the full article, please visit: http://www.npr.org/templates/story/story.php?storyId=96750869&ft=1&f=1025