Sep 26, 2008 12:54 PM | 1
The world's oldest rock has been found along the eastern shore of Hudson Bay in northern Quebec. The rock, a chunk of ancient volcanic deposits, is around 4.28 billion years old—or 250 million years older than the previous record-holder, the Acasta gneiss in northwestern Canada. That also makes them less than 300 million years younger than the Earth itself.
"There have been older dates from Western Australia for isolated resistant mineral grains called zircons," says geochemist Richard Carlson of the Carnegie Institution in Washington, who dated the old stone and reported its age this week in Science. But those zircons (which contain some of the world's oldest diamonds) were not actual rock like this bedrock. "This gives us an unprecedented glimpse of the processes that formed the early crust," Carlson says.
Carlson and his colleagues dated the Nuvvuagittuq greenstone by measuring variations in the amount of the rare elements neodymium and samarium to come up with an age of 3.8 to 4.28 billion years. The oldest rocks dubbed "faux ampholite" because they are like that modern volcanic rock, and the overall bedrock itself is similar to ocean floor that has traveled back up into the continental rock. It also suggests that perhaps early Earth was not as hot and roiling as the first geologic era's name—Hadean— might suggest.
But it is also possible that this rock is not unlike the zircon—mashed together remnants of older rock rather than a glimpse of the Earth's protean crust.
Credit: ©Donald Erickson/istockphoto.com
age of Earth,
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