Record concentrations of a helium isotope found inside 62-million-year-old Arctic rocks could be the most compelling evidence to date of a slow leak in our planet's core. Building on the results of a previous analysis of ancient lava flows, a team of geochemists from Woods Hole Oceanographic Institution and the California Institute of Technology are now more certain than ever that helium trapped in the core as our planet was forming is making its way to the surface. Helium isn't the kind of element that makes friends easily. Being so light and non-reactive, there's little to stop the gas from...