The Cold War may be over but its fallout still remains. Thanks to nuclear explosions  from these fearful decades, scientists can now work out if elephant tusks were illegally traded, or glean historical droughts from hippo teeth.

In the 1950s and 1960s, America and Russia repeatedly tested their new nuclear arsenals. The fallout from the explosions spread far and wide, blanketing the world in radioactive isotopes, such as carbon-14. This heavy form of carbon is normally a bit-player in the atmosphere, but levels rose so sharply during the Cold War that they created a noticeable spike—the bomb curve.

Some of the carbon-14 was converted into carbon dioxide and taken in by plants. Animals ate the plants and incorporated the carbon-14 into their