Basu and his colleagues suggest in Science that the material from Asia and Antarctica is from an impact event associated with the P-T mass extinction just as the impact crater in the Yucatán is now widely associated with K-T mass extinction.
Gregory Retallack, a geologist at the University of Oregon in Eugene who in 1995 collected one of the Antarctic samples analyzed by Basu and colleagues, also concluded that the rocks contained evidence of an asteroid impact.
"This new paper is a splendid corroboration of our earlier work," he said in an e-mail sent from Antarctica where he is currently searching for more impact beds associated with the P-T boundary.
Meanwhile, Basu and his colleagues are actively searching for an impact crater associated with the P-T mass extinction. Such a find, said Basu, would further clarify whether the impact occurred and, if so, its association with the mass extinction.
"The search is going on. So far in the published literature no one has found it, but we are working on it actively. We are working on it right now," he said.
Volcanic Isotopes
In a second Science study, geochemists analyzing the ratios of two osmium isotopes in seawater suggest that the bout of violent volcanic activity around the K-T boundary likely caused a major global warming event but was probably not a major contributor to the demise of the dinosaurs.
Greg Ravizza, a co-author of the study at the University of Hawaii in Honolulu, said the finding substantiates earlier studies based on analysis of the past climate by bringing more resolution to when the volcanism occurred in relation to the impact event.
"It's the first thing we have that substantiates the previous interpretations of the paleoclimate," he said.
The finding suggests that while the period of volcanism spanned the K-T impact event, the bulk of the volcanism occurred several hundred thousand years before the asteroid slammed into the Yucatán, causing the mass die off.
Ravizza said he would like to apply the dating technique he and his colleague Bernhard Peucker-Ehrenbrink of the Woods Hole Oceanographic Institution in Massachusetts used to the volcanism at the P-T boundary as well, but 250-million-year-old sediments on the seafloor are not well preserved.
Such work, if eventually possible, will help answer the still outstanding question of how significant a contribution the volcanism at the P-T boundary made to the mass extinction, versus the contribution of the impact.
Basu said it may even be possible that the volcanism at the P-T boundary is directly linked to the impact event. "That is the $64 million question," he said. "People are trying to figure out whether an impact could trigger volcanism. That would be a double punch."
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