This ancient section of the planet's crust may be as much as 4.28 billion years old, researchers report in today's edition of the journal Science.
While the age of the Earth itself is estimated at 4.6 billion years, most of the original surface has been crushed and recycled through tectonics, the movement of giant plates across the planet's surface.
By measuring tiny variations in the chemical composition of the Nuvvuagittuq greenstone from Hudson's Bay, researchers Jonathan O'Neil of McGill University in Montreal and Richard Carlson of the Carnegie Institution of Washington were able to date rock samples to between 3.8 billion and 4.28 billion years ago.
Previously the oldest piece of bedrock was the Acasta Gneiss in the Canadas's Northwest Territories, which is 4.03 billion years old.
Some zircon grains found in Western Australia have been dated to 4.36 billion years, but those are individual materials, not intact sections of bedrock.