GEOLOGY & PLANETARY SCIENCE A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site Acasta formation Orthogneisses, about 4 billion years old, with older enclaves of mafic rock, Slave Craton, Canada. Credit: Yuichiro Ueno, Tokyo Institute of Technology The oldest known outcrop of rock on Earth. It occurs about 350 km north of Yellowknife in Canada's Northwest Territories and consists of gneiss (a type of coarse-grained metamorphic rock) that dates back just under four billion years – to around the beginning of the period of late heavy bombardment. Related category    • GEOLOGY AND PLANETARY SCIENCE Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP