Canada home to world's oldest rocks, researchers say

Canadian and U.S. researchers say they have found the oldest rocks in the world, along the Northern Quebec coast of Hudson's Bay.

The rocks, found in an area known as the Nuvvuagittuq greenstone beltabout 40 kilometres south of Inukjuak, are estimated to be 4.28 billion years old, according to a team of researchers from McGill University, Universit du Qubec Montral (UQAM) and the Carnegie Institution for Science in Washington, D.C.

That would put the creation of the rocks at roughly 300 million years after the planet was formed, making them the oldest preserved piece of the Earth's early crust, researchers said Thursday.

Jonathan O'Neil, a Ph.D. candidate at McGill's department of Earth and planetary sciences and the lead author of a study to be published in Friday's issue of the journal Science, said the discovery would offer new insight into the early Earth.

"Our discovery not only opens the door to further unlock the secrets of the Earth's beginnings," said O'Neil in a statement. "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."

The rocks are known as "faux-amphibolites," taking their name from their resemblance to another class of rocks mostly composed of silica minerals. Unlike regular amphibolites, which are dark green or pitch black in appearance, rocks in this other classare beige or sugar brown, O'Neil told CBC News.

The researchers used isotopic dating, analyzing the decay of the radioactive elements neodymium-142 and samarium-146 to determine the age of the rocks.The technique is unique because of the instability of samarium-146. Although the isotope of the element was believed to have formed in the early Earth, remnants of it are extremely rare in all but the oldest rocks because it decays so quickly. That the researchers were able to find the isotope at all told them the rock was at least four billion years old, said O'Neil.

Finding remnants of the early Earth is extremely rare, said O'Neil. The oldest previously known rocks were found in an outcrop called the Acasta Gneiss, which lies southeast of Great Bear Lake in the northwestern corner of the Canadian Shield in the Northwest Territories.

Richard Carlson, a researcher at the Carnegie Institution for Science, Don Francis, a McGill professor in the department of Earth and planetary sciences, and UQAM professor Ross Stevenson were the paper's other authors.

O'Neil said the next step is to look at the chemical composition of more samplesfrom the same region in Northern Quebec.

"These rocks can give us clues as to how the first continents formed, but they may also tell us about atmospheric conditions and possibly the origins of life," he said.