Science 321, 1828–1831 (2008)

A beige outcrop in northern Quebec may be Earth's oldest known crustal rock. Jonathan O'Neil of McGill University in Montreal, Canada, and his colleagues have dated parts of the stone using ratios of neodymium and samarium isotopes, and calculated the oldest section to be 4.28 billion years old. This is 250 million years older than the previous record-holder.

The rocks in question are from the Nuvvuagittuq greenstone belt. This belt had been estimated to be 3.8 billion years old, based on an analysis of zircon crystals. But the stone that O'Neil and his team probed contained no zircons, forcing them to use an alternative method. The outcrop's low levels of neodymium suggest that it formed before Earth's neodymium levels became fixed 4.1 billion years ago.