


Acasta gneiss, Earth's oldest surviving rock
Acasta gneiss, oldest-known rock on Earth: is found in a small area of the Slave craton, a western province of the Precambrian shield of Canada. Rock that is approximately 4 billion years (4000 Ma, that is, million years) old is known over an area of about 40 km 2, about 150 km south of the Arctic circle (Bowring and Williams, 1999; Zimmer,1999).
