Fragments of iron pyrite, a rock that can be used with flint to make sparks, were found by a 400,000-year-old hearth in eastern Britain. Image: Jordan Mansfield/Courtesy Pathways to Ancient Britain Project

Fragments of iron pyrite, a rock that can be used with flint to make sparks, were found by a 400,000-year-old hearth in eastern Britain. Image: Jordan Mansfield/Courtesy Pathways to Ancient Britain Project