Face-off: PBS moderates on-line debate between proponents and detractors of Younger Dryas cosmic impact
“THE ICE AGE EXTINCTION DEBATE (UPDATE)
by Evan Hadingham, NOVA Senior Science Editor
In Megabeasts’ Sudden Death, NOVA reported on a radical new theory that an extraterrestrial impact devastated North America and other regions at the end of the Ice Age. First aired at a conference in May 2007 by a team led by geological consultant Allen West, the theory proposes that a comet or asteroid struck the ice sheets that covered most of Canada around 12,900 years ago. In an alternative scenario, the theory claims that a series of comet or meteor fragments burst in the atmosphere, similar to the Tunguska explosion that devastated a wide area of Siberia in 1908. In either case, according to the theory, the event ignited continent-wide firestorms and led to the extinction of about 35 types of giant animals, or “megafauna,” including mammoths, mastodons, lions, saber-tooth cats, and giant beavers. The event is also claimed to have reduced the populations of early Native American hunter-gatherers known as the Clovis people, and to have helped flip the Earth’s climate into a severe, final cold phase known as the Younger Dryas.
From its first announcement, the Younger Dryas impact theory sparked widespread controversy among archeologists, astronomers, and the science press. NOVA helped support an attempt to test the theory by a leading climate scientist, Paul Mayewski of the University of Maine, who searched for evidence of distinctive materials associated with impacts in the Greenland ice sheet. As shown in the program, West’s team analyzed Mayewski’s samples from Greenland and their results appeared to confirm the theory.
About a year after the first broadcast of NOVA’s show, several prominent astronomers and physicists who specialize in impact studies and are skeptical of the theory contacted NOVA. They argued that viewers needed to understand one of their key arguments—that an impact of the scale and type envisaged by West’s team was extremely improbable. In NOVA’s program, Sandia Lab physicist Mark Boslough briefly mentions this argument, but the reasoning behind it was not explained. NOVA therefore invited Boslough and astronomer Alan Harris of the Space Science Institute to write brief, non-technical essays about the improbability argument and other objections to the theory. To respond to these points, NOVA askedAllen West and one of his team, retired NASA impact specialist Ted Bunch, to respond to Boslough and Harris’s criticisms. The result is a snapshot of a highly intriguing debate that remains unresolved.”