Knowing how much chemistry there is between you and your date can be affected by nerves, emotions or even your surroundings.
"Corals are ideal materials for this kind of dating," says Sharp.
"They take in uranium from the seawater, but not thorium." Therefore, the coral would have stopped taking in uranium at the moment it was pulled from the sea.
The uranium-238 in the coral eventually decays into the more stable thorium-230, at a known rate.
Sharp used a mass spectrometer to measure the ratio of uranium to thorium in the coral and then, with a single age equation, calculated when the coral first grew on a reef. Some fell within a tight time span of just 30 years.