Meteorites and mammoths: who do you believe?

One of the wonderful things about science is that, well, it's never over.

Those questioning minds keep collecting data, probing and researching—and often what you assumed was settled knowledge isn't, any more.

Take the woolly mammoth.

(Image: That's it. Credit: Image of Woolly Mammoth at the Royal BC Museum, Victoria, British Columbia courtesy Wikipedia Commons.)

It roamed the Americas alongside modern humans—up to about 13,000 years ago, a time called the Younger Dryas.

And then the wooly mammoth was gone. Same with the fearsome saber-toothed tiger, and a bunch of sloths. Relegated to bone piles and tar pits.

For a long time, their extinction was blamed on a global climate cooling event, whose origins are complex. Some researchers believed it was associated with a slowing of the oceans' circulation patterns.

Then a couple of years ago, scientists, intrigued by finding the element iridium in rock layers from that period, suggested the iridium came from space and that the cooling was caused by an impact by some interstellar object. You know—the impact throws lots of dust into the atmosphere, the sun's radiation is blocked for a time, and things get real cold. And a lot of creatures die out.

But just as the scientific world was getting comfortable with that theory, along comes a team of researchers, led by a Hawai'i-based graduate student, François Paquay, of the Department of Geology and Geophysics at the University of Hawai'i at Manoa, to challenge that assumption.

His collaborators were a U.S.-Belgium-Canada team made up of Greg Ravizza of University of Hawai'i, Steven Goderis and Philippe Claeys from Vrije Universiteit Brussel, Frank Vanhaeck from the Universiteit Ghent, Matthew Boyd from Lakehead University, Todd A. Surovell from the University of Wyoming at Laramie, and Vance T. Holliday and C. Vance Haynes, Jr. from the University of Arizona at Tucson.

They started out expecting to validate the theory, “to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas,” said a University of Hawai'i press release. http://www.hawaii.edu/news/article.php?aId=3280

In a paper published this week in the Proceedings of the National Academy of Sciences, Paquay and his team said they looked for other indicators of an impact event. They had a number of problems. They couldn't locate an impact crater. They couldn't other indicators of extraterrestrial impact, notably isotopes of the element osmium. So they searched harder.

“Because there are so many aspects to the impact theory, we decided to just focus on geochemical evidence that was associated with it, like the concentration of iridium and other platinum group elements, and the osmium isotopes. We also decided to look in very high resolution sediment cores across North America,” Paquay said.

They looked at both marine and land-based sediment. They tested their sediment samples in laboratories both at the University of Hawai'i and in Belgium. No luck.

“We could find nothing in our data to support their theory,” he said.

But this debate is hardly over. Other folks are still doing research to support the idea of a meteorite impact.

And that's the way it is with science. The best evidence is only good until something better comes along.

© Jan TenBruggencate 2009