In this latest study, researchers examined the sedimentary material around the impact site and found it was far too violently churned up to provide a reliable dating record.As the article notes, however, other scientists are not so convinced. One of my friends from graduate school said at the time that dinosaurs show steep decline ahead of the K-T boundary and that they hang around for awhile after the boundary, suggesting that other factors were at work. This is echoed by Steven Salisbury of the University of Queensland, who is quoted in the article.
They found that farther away from the impact site, the sedimentary material becomes a single layer at the K-T boundary, matching the composition of rocks at Chicxulub.
They also determined that despite evidence for relatively active volcanism in India, ecosystems showed only minor changes within the 500,000 years before the K-T boundary event.
Only at the boundary do things suddenly change.
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