Heated Debate

Global fires may have doomed dinosaurs and much other life after giant meteorite struck Earth 66 million years ago

A new paper buttresses the theory that cataclysmic fires swept the globe 66 million years ago following a giant meteorite impact on the Yucatán Peninsula. Those blazes presumably spelled doom for the dinosaurs and much other life. Only a small number of creatures that could shelter themselves underground or underwater survived.

In 2004, lead author Douglas S. Robertson, a geologist at the Universityof Colorado, Boulder, and colleagues advanced the idea, which was first proposed by H. Jay Melosh of the University of Arizona in 1990. Robertson found support for the global fire hypothesis through evidence of the complete destruction of global terrestrial communities following the impact, and the fact that among nonaquatic animals, only the small ones survived. In addition, all nonaquatic survivors, including birds, seem to have been burrowers.

A number of papers, however, have since criticized the heat-fire extinction hypothesis, pointing, for example, to the relative absence of charcoal in the geological layers associated with the extinction event. New calculations of the sedimentation rate of charcoal, however, yield amounts consistent with a global fire hypothesis, the authors of the new paper note. They also suggest that the intense fires could well have burned up much of the charcoal. Another dispute involves the preservation of non-charred organic matter, which would appear to negate the possibility of global fires. But such material was collected at sites of swamps and ponds, where it would have sat safely underwater during the blazes.

The new paper also takes into account work that refined how the infernos started. Research published in 2009 suggests that the heat released into the atmosphere by debris falling back to Earth after the impact was insufficient to ignite trees directly, but that tinder—dry leaves and grass—could still have readily ignited.

Robertson considers that the evidence on the whole favors the heat-fire hypothesis. “Our model not only explains the extinction but gives details of what species survived and what didn’t—no other argument has that level of detail,” he said. “We think our argument is pretty solid right now, but there’s still some disagreement on the point.” (Journal of Geophysical Research–Planets)