单词：isotopic tracing
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This is Scientific American's 60-Second Science. I'm Cynthia Graber. This will just take a minute. The Earths crust is old. Billions of years old. So old that its nearly impossible to imagine. And now scientists have discovered what may be the oldest
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Artist James E. Taylor produced this sketch of the Freedmen's Bureau office in Richmond, Virginia, issuing food rations to old and sick former slaves in 1866 Some Americans can trace their heritage back to what we sometimes call the old country from
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Compston's machine allowed such rocks to be dated with unparalleled precision. 康普斯森的仪器能以无与伦比的精确度测定这些岩石的年代。 The prototype SHRIMP was built and machined in the Earth Science department's own worksho
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