Four Billion Years of History (image) University of Alberta Caption This four-billion-year-old rock sample from the Acasta Gneiss Complex in the Northwest Territories was used to determine how the Earth's earliest continental crust formed. Credit Bryan Alary/University of Alberta Usage Restrictions Photo credit. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.