Comets are believed by some experts to have wiped out megafauna species
The normally peaceable world of geology is currently alive with a fiery debate over the theory that deadly space rocks slammed into Northern Canada about 13,000 years ago, triggering a mini-Ice Age and the eventual extinction of the woolly mammoth and a host of other prehistoric species.
That contentious hypothesis – which has prompted a number of studies in recent years probing sites throughout North America for traces of the alleged extraterrestrial blast -is under renewed attack after a team of U.S. and British researchers published a paper last week arguing that previous claims of impact evidence are demonstrably mistaken.
The new study takes particular aim at several supposed discoveries of “nanodiamonds” at sites around North America -hailed by advocates of the impact theory as proof that a cosmic blast sent showers of “shocked” rock particles across the continent 13,000 years ago.
“The usefulness of cubic nanodiamonds as impact markers in sediments remains unclear because processes other than impact might account for them,” argues the new study led by Tyrone Daulton, a physicist at Washington University in St. Louis, and published in the latest Proceedings of the National Academy of Sciences.
The study also contends that the “nanodiamonds” documented in previous studies were, in fact, misidentified samples of a carbon-based substance called graphene that does not provide proof of a meteorite strike. But one of the researchers whose findings are targeted in the study -University of Oregon scientist Douglas Kennett -has shot back at Daulton, calling his work “fundamentally flawed science” that is unfairly discounting the impact hypothesis.
Randy Boswell Postmedia News
Woolly mammoths are one of several species of megafauna that some scientists believe became extinct following a comet-induced mini-Ice Age.
The controversy is focused on a thin rock layer seen around the world that represents the boundary of the Younger Dryas -a well-documented, 1,000-year period in Earth’s history, characterized by a sudden plunge in global temperatures beginning about 13,000 years ago.
The Younger Dryas cold spell roughly coincides with the arrival of humans in North America and with the precipitous decline and eventual disappearance of populations of mammoths, mastodons, sabre-tooth tigers, Ice Age horses and other creatures that once roamed the continent.
Some scientists have attributed the Younger Dryas deep-freeze and the subsequent string of megafauna extinctions to climate change caused by a massive meltwater outburst into the Atlantic Ocean -probably near present-day Hudson Bay – as Ice Age glaciers retreated north.
Others have blamed the abrupt loss of so many mammal species on over-hunting by early big-game hunters whose tribes had recently migrated to North America from Siberia.
About five years ago, studies began proposing the idea that a comet or asteroid might have struck a glacial ice dam near Hudson Bay, causing an initial catastrophe for North American ecosystems and then kick-starting long-term, global climate changes that wiped out the mammoths and their contemporaries.
Last year, several U.S. scientists headed by Kennett, unearthed a layer of what they called “nanodiamonds” on a California island, a find described at the time as “smoking-gun” proof that a massive comet triggered the Younger Dryas, killed off the mammoths and threatened the fragile foothold of North America’s earliest human inhabitants.
But Daulton says his team’s study disproves the theory because it shows that no nanodiamonds have been accurately linked to any of the North American sites.