More than 1500 years ago, a vast culture known as the Hopewell tradition (or Hopewell culture) stretched across what is today the eastern United States. The cause of the culture's decline has long been debated, with war and climate change two of the possibilities, but now a new avenue of inquiry has opened up: debris from a near-Earth comet. Researchers working across 11 different Hopewell archaeological sites covering three states have found unusual concentrations of iridium and platinum in their digging – telltale signs of meteorite fragments. Meanwhile, a charcoal layer in the sediment suggests an intense period of high...
