Age Estimate for Oldest Glacier Revised Way Down

first_imgDeposits from Antarctic glacial ice thought to be 8.1 million years old have been re-dated at not more than 310,000 years old, and maybe as little as 43,000, reports a team writing in the Feb. issue of Geology.1  Ng (MIT), Hallet, Sletten and Stone (U. of Washington) analyzed cosmogenic helium-3 and calculated the rate of sublimation of the ice to arrive at the new age estimate for glacial till (leftover rock debris from glacial melt or ice evaporation).  “Such rapid recent growth of the till contradicts previous interpretations that it is older than 8.1 Ma at an adjacent site, where it encloses volcanic ash of this age,” they say (emphasis added in all quotes).  “We question whether the ash provides a valid age constraint for the ice.”  Earlier geologists had dated the ash fall as a time constraint on the glacial till, but this team says it may accumulate much more rapidly than assumed.  “Our results show that the ash may not be a reliable stratigraphic indicator.”1Ng et al., “Fast-growing till over ancient ice in Beacon Valley, Antarctica,” Geology, Vol. 33, No. 2, pp. 121�124, doi: 10.1130/G21064.1.This team may not have the last word, either.  Readers should learn from this story that even among secular geologists, interpretations can contradict one another by orders of magnitude.  This is not just a story about dating methods, but also feeds into the debate about global warming.  Their paper begins, “The recent history of East Antarctica is key to understanding the response of large ice sheets to climate forcing.”  Beware political decisions based on advice from geologists who read present data and weave stories about things that happened millions of years ago, as if it will help forecast future events.  Considering revisions this large, politicians might be better off forecasting climate from analysis of layers in a calf’s liver.(Visited 20 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

Post A Comment

Your email address will not be published. Required fields are marked *