Resumen de Ancient crust comes up from the depths
Volcanic rocks found in the south Pacific spent at least 2.45 billion years on a journey into Earth's interior--and back again. To work out the age of that recycled ancient crust, Rita Cabral of Boston University and her colleagues analyzed the sulphur isotopes in Mangaia's basalt rocks. They found that some of the isotopes were ones that can only form via a reaction in the presence of intense light. This must have happened before the atmosphere contained much oxygen, because once the gas formed a primitive ozone layer, very intense light no longer reached Earth's surface. Since the Earths atmosphere first carried measurable quantities of oxygen around 2.45 billion years ago, the crust must have formed and been subducted at least this long ago, Cabral reasons.
