FEW editors can resist a disaster story, even one that happened in the distant past. So it is little wonder that the press jumped all over claims by a team of 25 researchers in 2007 that a mysterious impact on the North American ice sheet 12,900 years ago wiped out the continent鈥檚 Pleistocene megafauna and the Clovis culture of the early settlers, and wreaked havoc on the global climate. The researchers claim a comet collision triggered wildfires across the continent and a sudden cooling known as the Younger Dryas event. If correct, the theory could help resolve a long-running debate over whether climate change or the first human settlers killed off the mammoths and other ice-age giants.
The story got a fresh airing in January when (vol 323, p 94) appeared to back it up. Yet despite this, there is very little support for the impact theory. Specialists in several fields see no convincing evidence of a smash. A study in the Proceedings of the National Academy of Sciences last week () found no sign of continent-wide wildfires. Needless to say, the press paid little heed: who wants a good story ruined by a few facts?
Beware. In geology, bold explanations for Earth-changing events rarely match up to reality. Our environment was shaped mainly by long-term processes rather than catastrophes. Reporters tend to find such slow change boring, and focus on dramatic events such as earthquakes. Unfortunately, they also fall for fancifully dramatic explanations.
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One such was the catastrophism of , whose 1950 book Worlds in Collision was a bestseller. Scientists spent years debunking Velikovsky, but within a year of his death, Luis and Walter Alvarez made headlines with the idea that a 10-kilometre-wide asteroid caused the extinction of the dinosaurs 65 million years ago. The Alvarezes had solid evidence which other scientists then replicated. Naturally, this encouraged researchers to blame other mass extinctions on cosmic collisions, a conclusion the press was always happy to celebrate.
Fair enough: if such an event can happen once, it can happen again. Yet no one has convincingly linked any other mass extinction to an asteroid impact. The dinosaur-killer could have been one of a kind. Take note: no matter how intriguing a theory sounds, the real test is whether its predictions match the facts.