Nature: Cratons are the oldest, most stable parts of Earth’s crust, and as such hold clues to Earth’s early evolution.Dewashish Upadhyay, a geochemist now at the Indian Institute of Technology in Kharagpur, analyzed the make-up of isotopes in rocks from India’s Bastar craton and found that some of the rocks carry the signature of a differentiation event—the separation of materials with different geochemical properties.This event must have taken place during the first 400 million years of Earth’s history, possibly when a magma “ocean” covering the planet solidified. Related Link142Nd evidence for an enriched Hadean reservoir in cratonic roots