Figure 10.22Newly discovered rocks show that continental crust existed on Earth’s surface during the Hadean eon. (a) The Acasta gneiss from the Slave craton has been dated at 4.0 billion years old. (b) Amphibole-bearing rocks from the Nuvvuagittuq greenstone belt, northern Quebec, Canada, have been dated at 4.28 billion years ago, making them the oldest rock formation yet discovered.