Study Raises Doubt about Ancient Giant Comet Explosion
A University of Wyoming professor contributed to an international study published this month by the Proceedings of the National Academy of Sciences (PNAS) that casts doubt on the theory that a giant comet exploded over the continent some 13,000 years ago and sparked a cooling period known as the Younger Dryas.
Thomas Minckley, an assistant professor in the UW Department of Botany, provided data on biomass burning, or the burning of living and dead vegetation. The study links rapid climate change to the fire activity at the end of last Ice Age and the warm interglacial period that began about 11,700 years ago but does not support the cometary impact hypothesis.
Charcoal particles left by wildfires in sediment from 35 North American lakes, along with tree pollen, serve as the basis of the paper, titled "Wildfire responses to abrupt climate change in North America." The study was published in the Feb. 3 edition of PNAS.
Minckley and his colleagues' initial look at the data was prompted by the Firestone "Younger Dryas comet hypothesis," which includes the idea that a comet impact resulted in continental-scale fires and wiped out large mammals like woolly mammoths and mastodons, and affected prehistoric humans.
"The comet hypothesis is sexy, but our paper shows that the main control of changes in biomass burning is climate--rapid climate changes stress vegetation and create conditions that support large fires," Minckley says. "In fact, one of the biggest clusters of fires occurred at the end of the cold interval, as opposed to its beginning, and that's another problem for the comet hypothesis.
"Overall, I think the simplest explanation for the biomass burning record is climate change and when climate abruptly warms, burning increases, like it seems to be doing over recent decades."
University of Oregon doctoral student Jennifer R. Marlon led the collaborative study of 23 co-authors at institutions in the United States, Canada and Europe. She says her team's analysis of charcoal and pollen records shows no evidence of continental-scale fires suggested in the Firestone hypothesis.
"The charcoal data doesn't support the idea of widespread fires at the beginning of the Younger Dryas interval," adds Patrick J. Bartlein, Marlon's adviser and a professor of geography at Oregon. "The results don't reject the comet hypothesis, but do suggest that one element of it -- widespread fires -- didn't occur. Instead, the data show that biomass burning tracked general climate changes closely."
Posted on Thursday, February 12, 2009