The old tales may be true: There is brimstone in the underworld, and lots of it. Brimstone, the biblical name for sulfur, is often found near hot springs and volcanic fissures on Earth’s surface (above). But scientists studying the formation of Earth’s core have shown that the lightweight nonmetal might also be present there in vast quantities, answering a question that has long troubled earth scientists: How could Earth’s core—predominantly made of the heavy elements iron and nickel—appear as light as it does when analyzed using seismic waves? Researchers report online today and in the July issue of Geochemical Perspectives Letters that the answer may be sulfur trapped deep within Earth. To come up with their results, the team compared the proportions of copper isotopes in ancient meteorites—the presumed building blocks of our planet—with the proportions of copper isotopes in rocks originating from the mantle—the deep layer of viscous rock beneath Earth’s crust.