Earth's ancient continental crust, found in outcroppings along the eastern shores of the Hudson Bay, was formed from re-melted oceanic-type rocks forged more than 4.2 billion years ago. Photo by Jonathan O'Neil/Carnegie Science
March 17 (UPI) -- Determining what exactly Earth's earliest crust was like has proven difficult for geologists. But new analysis has offered researchers a window into Earth's crustal past.
Scientists discovered the chemical signatures of early Earth's crust in rock samples recovered in Canada.
"Finding remnants of this ancient crust has proven difficult, but a new approach offers the ability to detect the presence of truly ancient crust that has been reworked into 'merely' really old rocks," Richard Carlson, a geologist at the Carnegie Institution for Science, said in a news release.
Researchers found the ancient crust by locating neodymium-142, an elemental isotope create by the decay of samarium-146, an extremely rare elemental isotope found in only the oldest rocks.
Samarium-146 ceased to exist when the Earth was only 4 billion years old. Researchers were able to identify ancient rock remnants by analyzing the ratios of neodymium isotopes.
Isotopes are iterations of an element with different numbers of neutrons, and thus, different masses.
Carlson and his colleague, Jonathan O'Neil of the University of Ottawa, discovered an abundance of neodymium-142 -- the derivative of decayed samarium-146 -- in 2.7 billion-year-old granitic rocks excavated from the east shore of Canada's Hudson Bay. Their findings, detailed in the journal Science, suggests the Canadian rocks are derived from rocks that were formed, melted and recycled some 4.2 billion years ago.
Earth's earliest crust looked much like the basaltic rock found in oceanic plates today, scientists say. The early crust likely formed shortly after Earth's formation and survived for 1.5 billion years.
"Whether this result implies that plate tectonics was not at work during the earliest part of Earth history can now be investigated using our tool of studying neodymium-142 variation to track the role of truly ancient crust in building up younger, but still old, sections of Earth's continental crust," Carlson said.