Washington: An international team of scientists has found no evidence supporting a meteorite impact event at the onset of the Younger Dryas - 13000 years ago.
The Younger Dryas is an abrupt cooling event in Earth’s history.
It coincided with the extinction of many large mammals including the woolly mammoth, the saber toothed jaguar and many sloths.
This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America.
This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorise that an impact event was instead the instigator of this climate shift.
A team led by Francois Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this 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.
To corroborate the theory, Paquay and his colleagues decided to take a three-pronged approach.
The first was to replicate the original researchers data, the second step was to look for other tracers, specifically osmium isotopes, of extraterrestrial matter in those rocks, and the third step was to look for these concentrations in other settings.
“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,” said Paquay.
“We also decided to look in very high resolution sediment cores across North America, and yet we could find nothing in our data to support their theory,” he added.
Both the marine and terrestrial sediment records do not indicate that an impact event was the trigger for the transition into the Younger Dryas cold period.
“The marine and terrestrial record both complement each other to support this finding,” concluded Paquay.