June 8, 2009
Ancient Rocks Reveal Ages
Billions of years of history have been uncovered with a new technique that is helping scientists paint a picture of how Earth's continents were arranged.
Scientists are using the new method to recover rare minerals from rocks and analyze their composition. In addition, researchers claim they can accurately date ancient volcanic rocks for the first time.
The early landmasses can be pieced together by aligning rocks that have a similar age and orientation. Scientists say the new approach will help them discover rocks rich in ore and oil deposits.
So far, the method has revealed that Canada once bordered Zimbabwe, helping the mining industry identify new areas for exploration.
Dr Wouter Bleeker, from the Geological Survey of Canada, said much of the geology that exists today formed around 300 million years ago when the supercontinent Pangea existed.
"We really don't understand the [Earth's] history prior to Pangea," he told a recent meeting of the American Geophysical Union in Toronto.
The geologists reconstruct early landmasses by analyzing rocks that formed when continents drifted apart.
Dr Richard Ernst, a geologist from the University of Ottawa, said molten magma fills the cracks formed by shifting continental plates.
The magma cools to form long veins of basalt that has a "distinct magnetic signature" revealing the rock's orientation and latitude when it formed.
Researchers combine this "magnetic signature" with the ages of the rocks, to determine whether rocks on different continents were once part of the same volcanic up-welling.
Until now, researchers were unable to determine the ages of these ancient rocks due to problems with extracting the minerals used to date them. The mineral crystals were too small, usually far smaller than a strand of human hair.
Thanks to the development of baddeleyite, the minerals can now be successfully recovered. Baddeleyite incorporates large amounts of uranium into its crystal-structure.
Uranium naturally decays to lead, and because scientists know the rate at which this happens they can use these minerals as radioactive "clocks".
Researchers hope to collect and date 250 rocks from around the world during a large international project.
They plan to use this information to reconstruct how these continental fragments were once together to form giant landmasses that existed 2.5 billion years ago.
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AGU Joint Assembly 2009