Primordial NukesThe 2-billion-year-old tale of Earth's natural nuclear reactors Peter Weiss For more than a decade, Alexander P. Meshik has kept close tabs on a fleck of black rock no larger than an infant's fingernail. It's so unassuming that most people would sweep it into a dustpan without a second thought. Yet to Meshik, a nuclear physicist originally from Russia, this little scrap of mineral is a scientific gem. E. Roell The fleck, with its clues to believe-it-or-not geophysical events, emerged from the bowels of Earth decades ago. It was unearthed in the early 1970s at the Oklo uranium mine...