outpourings known as flood basalts that were similar to the Deccan Traps eruptions. The gases spewed from these eruptions probably caused worldwide climate devastation,
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, including short-term cooling and a progressive increase in greenhouse gases and ocean acidification. Gases from the Deccan eruptions have been suspected as a possible cause of the Late Cretaceous extinction,
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, but scientists didn’t know exactly when the volcanism happened relative to the extinction event.
Previous dating of the Deccan Traps used the decay of radioactive potassium atoms in the rocks. This technique produced uncertainties of more than 1.4 million years — longer than the volcanic event itself. To create a more precise timeline, Keller and colleagues instead looked at crystals called zircons,
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, which form during volcanic eruptions.
As zircons grow inside pools of magma, they absorb uranium atoms. Over time,
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, the embedded uranium slowly decays into lead. By comparing the relative number of uranium and lead atoms in the crystals,
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, scientists can estimate how long ago the zircon formed. “The crystals are like little time capsules,
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,” says lead author Blair Schoene,
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, a geologist at Princeton.
Flood basalts such as the Deccan eruptions don’t produce many zircons, however, and two expeditions to India left the team empty-handed. In December 2013, the researchers finally uncovered a few crystals in rock layers reddened by oxidation. The oxidation, a sign of weathering,
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, suggests the layer was at the surface for an extended period of time.
The crystals in these weathered rocks may

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