Science News reports:

Which came first: the impact or the eruptions? That question is at the heart of two new studies in the Feb. 22 Science seeking to answer one of the most hotly debated questions in Earth’s geologic history: Whether an asteroid impact or massive volcanism that altered the global climate was mostly to blame for the demise of all nonbird dinosaurs 66 million years ago.

The dinosaur die-off is the only known mass extinction that coincides with two cataclysmic events: an asteroid impact linked to the massive Chicxulub crater in Mexico, and a gigantic volcanic eruption, evidenced by kilometers-thick layers of hardened lava at India’s Deccan Traps. The extinction marks the boundary between the Cretaceous and Paleogene periods, or the KPg boundary.

Using two different geochemical dating techniques, two separate teams dated the lava flows. The goal was to try to determine whether the bulk of the lava predates or postdates the KPg boundary. Both estimated that the eruptions lasted in total about 1 million years. But one team, using uranium-lead dating, found that some of the biggest pulses of lava erupted tens of thousands of years before the KPg boundary. The other team, using argon-argon dating, determined that three-fourths of the lava erupted afterward. [Continue reading…]