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. (Jordan Mansfield | Courtesy Pathways to Ancient Britain ...

It's easy to take for granted that with the flick of a lighter or the turn of a furnace knob, modern humans can conjure flames — cooking food, lighting candles or warming homes. For much of our ...