Every Rock Has A Story - Acasta Gneiss

Gneiss is a high grade banded metamorphic formed by the deep burial and heating of its pre-existing parent rock. This specimen the Acasta Gneiss from the NW territories of Canada is the Earth’s oldest known intact rock and one of its it’s earliest vestiges of continental crust. Radioisotope dates on zircon crystals in the gneiss indicate an age of ~4.03 Byr – some zircon crystals surviving from its parent granite are 4.2 Byr. Zircon crystals retain their original composition at very high temperatures thus allowing for dating of earth’s old metamorphic rocks.