The mountain glaciers in Yosemite National Park are predicted to melt within 75 years. Now, a new study shows that their loss is the first time humans have seen the ice-free mountains of Sierra Nevada.
According to a new study published Wednesday (October 1) in the journal Science Advances, Sierra Nevada glaciers have not disappeared since the last ice age. It means that people have never witnessed an ice-free Sierra Nevada, as they reached their maximum range around 30,000 years ago, and humans are not thought to have arrived in North America until 30,000 years ago.
You might like it
Geoscientists have long known that the current western glaciers’ range of western United States has reduced over the past 11,700 years and is growing in a time frame known as the Holocene. During the warm early Holocene, the Sierra glacier became smaller and then expanded again in the mid- to late Holocene. They have shrunk in the last century, shrinking from the dreaded ice walls hanging over the rugged slopes into small snow fields that barely cling to beings.
What’s unclear was whether these glaciers had completely disappeared. Several studies of glacial deposits in lakes beneath ice suggest that they may have disappeared in the early Holocene just to reform three thousand years ago.
To take a more clearer photo, researchers tested rock samples and recently exposed bedrock from near four retreating glaciers inside and near Yosemite National Park: Conness, Maclure, Lyell, and Palisade. They were looking for specific variations of the carbon and elemental beryllium, which are only formed when cosmic rays from the sun hit the rock.
These variations do not form when rocks are buried from the sun and evacuated, thus their presence becomes apparent when the rocks are exposed. And it also offers a “clock” that gives the date of its exposure, as variations collapse at known speeds.
The results suggest that these long-term rocks beneath the glacier have been exposed for less than 100 to thousands of years, and none of the glaciers have completely disappeared. This is a track along with the current trends in global warming, the research author wrote:
Before the Holocene, during the Ice Age – scientifically known as the Last Ice Age – the Sierra Nevada Glacier would have peaked about 30,000 years ago. It has been confirmed that humans lived in North America 23,000 years ago. Some controversial archaeological evidence places people in northwestern New Mexico about 30,000 years ago. In any case, humans are unlikely to turn to the iceless Sierra Nevada.
“[Our] The reconstructed glaciers’ history shows that future glaciers-free Sierra Nevada is unprecedented in human history,” the author writes.
Source link
