An analysis of the distribution of helium-isotope ratios in oceanic extrusions from Earth's mantle seems to establish a connection with the spread of ages in continental crust. What mechanism might underlie this? After decades of intensive study, fundamental questions remain about the chemical composition and evolution of Earth's interior. On page 900 of this issue, Parman1 reports on an analysis of helium-isotope ratios in basalts found in oceanic islands and derived from Earth's mantle. He finds an intriguing correlation between the distribution of helium ratios — a chemical indicator of mantle history — and the age-distribution of rocks in Earth's continental crust.
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