McGill researchers find oldest rocks on Earth

Discovery of rocks as old as 4.28 billion years pushes back age of most ancient remnant of Earth’s crust by 300 million years

McGill University researchers have discovered the oldest rocks on Earth – a discovery which sheds more light on our planet’s mysterious beginnings. These rocks, known as “faux-amphibolites”, may be remnants of a portion of Earth’s primordial crust – the first crust that formed at the surface of our planet. The ancient rocks were found in Northern Quebec, along the Hudson’s Bay coast, 40 km south of Inukjuak in an area known as the Nuvvuagittuq greenstone belt. Their results will be published in the September 26 issue of the journal Science.

The discovery was made by Jonathan O’Neil, a Ph.D. candidate at McGill’s Department of Earth and Planetary Sciences, Richard W. Carlson, a researcher at the Carnegie Institution for Science in Washington, D.C., Don Francis, a McGill professor in the Department of Earth and Planetary Sciences, and Ross K. Stevenson, a professor at the Université du Québec à Montréal (UQAM).

O’Neil and colleagues estimated the age of the rocks using radioactive dating, which analyzes the isotope neodymium-142 within them, produced from the decay of the isotope samarium-146. This technique can only be used to date rocks roughly 4.1 billion years old or older; this is the first time it has ever been used to date terrestrial rocks, because nothing this old has ever been discovered before.

The data from these findings will give researchers a new window on the early separation of Earth’s mantle from the crust in the Hadean Era, said O’Neil.

"Our discovery not only opens the door to further unlock the secrets of the Earth’s beginnings," he continued. “Geologists now have a new playground to explore how and when life began, what the atmosphere may have looked like, and when the first continent formed.”