help geologists reconstruct maps of long-lost supercontinents. The dike above,
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, at Singhbhum craton near Keonjhar,
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, India, is about 1.7 billion years old. ~~ Courtesy Of J. Meert" />A team led by geologist Richard Ernst of Carleton University in Ottawa,
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, Canada,
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, recently explored the relative positions of Laurentia and Siberia between 1.9 billion and 720 million years ago,
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, a period that spans both Nuna and Rodinia. Ernst’s group specializes in studying “large igneous provinces” — the huge outpourings of lava that build up over millions of years. Often the molten rock flows along sheetlike structures known as dikes,
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, which funnel magma from deep in the Earth upward.
By using the radioactive decay of elements in the dike rock, such as uranium decaying to lead, scientists can precisely date when a dike formed. With enough dates on a particular dike, researchers can produce a sort of bar code that is unique to each dike. Later,
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, when the dikes are broken apart and shifted over time, geologists can pinpoint the bar codes that match and thus line up parts of the crust that used to be together.
Ernst’s team found that dikes from Laurentia and Siberia matched during four periods between 1.87 billion and 720 million years ago — suggesting they were connected for that entire span, the team reported in June in Nature Geoscience. Such a long-term relationship suggests that Siberia and Laurentia may have stuck together through the Nuna-Rodinia transition,
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, Ernst says.
Other parts of the puzzle tend to end up in the same relative locations as well, says Joseph

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