Nature, Published online: 11 November 2026; doi:10.1038/d41586-026-03499-w

Ancient rocks in northern China reveal that by 3.95 billion years ago, surface-altered oceanic crust had been buried rapidly to depths greater than 50 kilometres and partly melted. This crust was derived from a mantle reservoir that had been left behind when the crust separated from the early mantle as early as 4.3 billion years ago.