U.S. researchers from the Carnegie Institution of Washington and Canadian scientists from McGill University in Montreal determined an age of 4.28 billion years for rock samples taken from the Nuvvuagittuq greenstone belt, making it 250 million years more ancient than any previously discovered rocks.

The Nuvvuagittuq greenstone belt -- an expanse of bedrock exposed on the eastern shore of Hudson Bay in northern Quebec -- was first recognized in 2001 as a potential site of very old rocks.

Samples of the Nuvvuagittuq rocks were analyzed by geologists Jonathan O'Neil of McGill University and Richard Carlson of the Carnegie Institution. By measuring minute variations in the isotopic composition of the rare earth elements neodymium and samarium in the rocks, O'Neil and Carlson said they determined the rock samples range from 3.8 billion to 4.28 billion years old.

Before the study, the oldest dated rocks were from a body of rock known as the Acasta Gneiss in the Northwest Territories, which are 4.03 billion years old.

The findings appear in the journal Science.