The shells of chelonians—think turtles, tortoises, and sea turtles—grow in layers, keeping a time-stamped record of environmental conditions. Uranium has shown up in the layers of turtles’ and ...

In cartoons, when a turtle is spooked, it retreats into and closes up its shell. While used for comic effect, this imagery is based in fact – although not all turtles are capable of this protective ...