Earth’s Earliest Crust

The scarcity of rocks preserved from the first billion years (Gy) of Earth’s history hinders our ability to study the nature of the earliest crust. Rare >4.0-Gy-old zircons confirm that felsic crust was present within 500 million years of Earth’s formation. Given that most of that ancient crust has been destroyed, geochemical and isotopic tracers applied to rocks from the oldest sections of continents can be used to provide insights into the nature of the predecessor crust. Evidence from Earth’s oldest rocks and minerals suggests multiple early mantle depletion episodes, possibly linked to the formation of an initial, dominantly mafic, crust. This early crust was the precursor to evolved rocks that now constitute considerable portions of Earth’s oldest surviving crust.