Issue Date: September 29, 2008
Earth Shows Its Age
Using neodymium-based isotope dating, Jonathan O'Neil of McGill University, in Montreal, and colleagues have identified what could be the oldest rocks ever found on Earth (Science 2008, 321, 1828). The researchers collected the samples from the Nuvvuagittuq greenstone belt, an expanse of exposed bedrock on the eastern shore of Hudson Bay in northern Quebec. The rocks are composed of cummingtonite, plagioclase, biotite, and quartz, and in some cases they also contain garnet. The team measured ratios of 142Nd, 143Nd, and 147Sm to 144Nd in order to date the rock samples. The results indicate that the rocks are 4.28 billion years old, which suggests the formation "may represent the oldest preserved crustal section on Earth," which itself is some 4.6 billion years old, the researchers note. Samples collected at the Acasta gneiss in Canada's Northwest Territories held the former record of 4.03 billion years for whole rocks. However, isolated zircon mineral grains that formed some 4.36 billion years ago have been found in Western Australia.
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