Earth Sciences Prof Finds Oldest Rocks on Earth

August 24, 2010

Professor of Earth Sciences Matt Jackson and four colleagues from other institutions recently discovered the oldest rocks on the planet. Their findings were published in Nature on August 12. Surveying Cenozoic-era lavas on Baffin Island in Canada and in West Greenland, they found primitive lead-isotope ratios that indicate they formed in the ancient Earth’s mantle roughly 4.5 billion years ago.

They also found ratios of neodymium isotopes (specifically 143Nd/144Nd) similar to values recently proposed for terrestrial mantle reservoirs of roughly the same age (4.5 billion years). The researchers also found that the lavas in the area had extremely high ratios of helium (specifically 3 He/4He) — an indicator that the lavas are ancient, primitive materials from Earth’s mantle.

The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most-ancient accessible reservoir in the Earth’s mantle, and may be the origin of all mantle reservoirs that give rise to modern volcanism. Previously, it was thought that vigorous mantle mixing and subduction injection of oceanic material into the mantle had destroyed all early-formed mantle reservoirs. These lavas provide the first evidence that distinct portions of the mantle may survive intact over the age of the Earth.

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