Dark matter makes up 83 percent of all the stuff in the universe. To try to detect it, scientists need a radiation-free environment. To that end, they've built labs deep underground, where surface radiation can't get through and interfere. But background radiation from everyday radioactive materials is a major contaminant. The solution? Old lead from ancient shipwrecks. Lead can shield detectors from all kinds of radiation if it's not radioactive itself. Ancient lead is ideal, not just because its unstable lead-210 isotope would have largely decayed away over the centuries into stable lead-206, but also because the sea has shielded it from cosmic rays, which can kick-start a material’s radioactivity. So where alchemists failed, modern scientists have finally succeeded at "transmuting" lead into gold, and the search is on for these shipwrecks.