Water has not flowed across Antarctica’s Friis Hills for 14 million years, researchers reported Tuesday (Oct. 29) at the Geological Society of America’s annual meeting in Denver.
The Friis Hills rise 2,000 feet (600 meters) above Antarctica’s Taylor Valley, one of the “Dry Valleys” west of McMurdo Sound. Fossils show tundra mosses and a lake once covered the flat-topped hills, when Earth’s climate was warmer more than 14 million years ago. Now, thanks to blocking by nearby mountains, cold temperatures and strong winds that suck moisture from the air, the aptly named Dry Valleys receive little to no measurable rain or snow. (Sometimes, snow drifts in from nearby hills.)
To gauge ancient rainfall amounts, Rachel Valletta, a graduate student at the University of Pennsylvania, looked for traces of a radioactive isotope called beryllium-10 in lake sediments on the Friis Hills. This rare beryllium isotope, which has more neutrons than the stable version, forms when cosmic rays collide with oxygen and nitrogen atoms. Beryllium-10 decays on a predictable time scale, allowing geochemists to estimate the age of sediments containing the isotope. [The 10 Driest Places on Earth]
Valletta tested the lake sediments for meteoric beryllium-10 — isotopes created in Earth’s atmosphere and carried down to the surface by
source : livescience