For the last five years or so science journalists have repeatedly caught the public up on a radical, and beguiling, impact hypothesis to explain why North America lost much of its huge beasts, or megafauna, as the last ice-age glaciation in North America zig-zagged toward its end. The speculation – one that is not zany but has also not won much respect either from the academic main stream – holds that about 12,900 years ago a shower of comet or asteroid chunks air-burst over the continent. The blast set off a cascade of changes that wiped out mammoths, ground sloths, cave bears, saber tooth cats, dire wolves, and other iconic, now fossilized creatures. It may also have helped to kick off a prolonged re-cooling and extension of the Pleistocene ice sheet that geologists call the Younger Dryas. So say adherents of this story, so wonderful in scope and drama. It has had enough profile even to be the focus of television specials. But not recently.
Here is a list of eleven previous posts on the topic. To save you time counting, we had six in 2007, two in 2008, two in 2009; one in 2010; none since until this one. If you follow that link, you’ll perhaps notice that our posts had in their headlines a trend toward skepticism. I believe, and of course I do since I wrote the posts, that this headline trend is an objective interpretation of the news stories and the research results behind them.
Just to put an exclamation mark on what ksjtracker already has gathered, here’s one from last year, at Miller-McCune by Rex Dalton. It underscored the trend with a hammer blow of a story. Included were suspicions of fraud – although they addressed the character and history of one of the proposal’s adherents but did not directly say there is proven fraud (but perhaps contamination) in the data. The word nonsense comes up. Dalton’s characterization in the story got stern rebuttal from one adherent of the hypothesis.
So! Earlier this month a research team that includes some of the idea’s original backers wrote in the Proceedings of the National Academy of Sciences that sediment from a lake in Mexico reinforces the hypothesis. There are nanodiamonds indicative of a major shock wave in the crust, and spherules or roundish bits that look like cooled droplets of bedrock melted and sprayed out from violent events. The abstract’s and full text are reachable via Grist below. UC Santa Barbara’s press office put out a strong press release, declaring that the lakebed surrendered a precisely dated layer with inclusions “conclusively identified” as uniquely associated with cosmic impact.
Whey tell you all this? A tracker reader and acquaintance who has helped to build this concept sent a note asking for anonymity, and also asking how come the story got little coverage and none at ksjtracker?
First up, there are some stories that ran, but not many:
- PopSci – Rebecca Boyle: Massive Extraterrestrial Rock Hit Earth 14 Millennia Ago, According to Nano-Evidence; A decent narrative recap of the hypothesis’s history, with no opinion however from skeptics on the new paper. This came out swiftly on the heels of the press release, written on short deadline, one assumes.
- Discovery News – Irene Klotz: New Clovis Comet Clues From Mexico ; A short, straight summary of the paper. No hint of the background to-and-fro over the idea that has already occurred among scientists.
- Space.com – Clara Moskowitz: New evidence that asteroid hit Earth 13,000 years ago ; Another straight summary of the researchers’ interpretation of their data, with passing reference to skeptics.
- Universe Today – Jason Major: Mexican Lake Bears Witness To Ancient Impact ; Looks to be largely off the UC Santa Barbara press release.
- Wall Street Journal – Matt Ridley: A Global-Cooling Theory Gets a Second Chance ; A somewhat loopy column that argues, first, that scientists are a lot like lawyers arguing a case rather than scholars or philosophers testing their theories, very willing to ignore data that don’t fit their concepts. After thus leveling the field of argument as more rhetorical than anthing else, it suggests that if the impact hypothesis for the Ice Age’s Younger Dryas cooling era is getting a second hearing, then perhaps the academy’s confirmation bias is not insurmountable after all. Perhaps there is some other wing of climate science, this English essayist seems to be hinting, that is due for comeuppance.
- Orange Country Register – Pat Brennan: Did cosmic impact kill the mammoths? ; Presents no contrary opinion.
- io9 – Alasdair Wilkins: Were woolly mammoths and saber-tooth cats wiped out by a giant impact from space? A journalist’s blog post, skeptical but not dismissive.
The ultimate trajectory of this hypothesis is impossible to predict. But the relatively small news splash is easier to explain. A few more nanodiamonds and spherules, one guesses, are not enough to change the Mammoth Comet idea from hypothesis to sober, central theory that merits big play.
In the meantime, among the principals the issue remains hot..Doubt among experts is rife. Persistence by its adherents is fierce. My opinion, just an opinion, is that it will linger for years on the fringe, and fade. Maverick ideas tend to do that. There are exceptions. Wegener’s drifting continents got the cold shoulder, at first, from many early 20th century specialists. Now it is the field’s bed rock principle. The late Lynn Margulis put up with ridicule for years after she proposed that many of our cells’ organelles, including mitochondria, are descended from independent bacteria that got engulfed by cells of another species a long time ago – now such endosymbiosis is embraced.
And answering the email I got, the reason for not posting on this earlier this month is partly that I made a note of it and didn’t get back for a hard look. Another reason is that this looks like incremental new evidence to me, and like a lot of other reporters, and outlets that look at their past stories for daily guidance, it would have been hard to muster the energy for another dive. Now I’m glad I did, if only to remind myself how much media attention it has gotten already and to see the marked drop-off.
Grist for the Mill:
PNAS article : Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis; UC Santa Barbara Press Release ;
– Charlie Petit