Earth’s early history told by 3.9-billion-year-old rocks from northern China

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. Zircon crystals found in some of Earth’s oldest rocks suggest that the source rock was once buried about 50 kilometres into the mantle.