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So a team of university scientists and a NASA colleague were greatly surprised to discover an ancient tundra landscape preserved under the Greenland Ice Sheet, below two miles of ice.
“We found organic soil that has been frozen to the bottom of the ice sheet for 2.7 million years,” said University of Vermont geologist and lead author Paul Bierman. The finding provides strong evidence that the Greenland Ice Sheet has persisted much longer than previously known, enduring through many past periods of global warming.
Greenland is a place of great interest to scientists and policymakers because the future stability of its huge ice sheet — the size of Alaska — will have a fundamental influence on how fast and high global sea levels rise from human-caused climate change.
“The ancient soil under the Greenland ice sheet helps to unravel an important mystery surrounding climate change,” said Dylan Rood, a co-author on the new study, from the Scottish Universities Environmental Research Centre and the University of California, Santa Barbara. “How did big ice sheets melt and grow in response to changes in temperature?”
The new discovery indicates that even during the warmest periods since the ice sheet formed, the center of Greenland remained stable. “It’s likely that it did not fully melt at any time,” Bierman said. This allowed a tundra landscape to be locked away, unmodified, under ice through millions of years of global warming and cooling.
“Some ice sheet models project that the Greenland Ice Sheet completely melted during previous interglacial periods. These data suggest that did not happen,” said co-author Tom Neumann, a cryospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “We don’t know how much of the ice sheet remained – to estimate it, we’d have to study other ice cores in Greenland that have sediment in the bottom to see if ancient soil is preserved under those sites as well.”
The scientists tested seventeen samples of “dirty ice” – ice with sediment mixed in — from the bottommost 40 feet of the 10,019-foot GISP2 ice core extracted from Summit, Greenland, in 1993. From this sediment, Bierman and a team at the University of Vermont’s Cosmogenic Nuclide Laboratory extracted a rare form of the element beryllium, an isotope called beryllium-10. Formed by cosmic rays, it falls from the sky and sticks to rock and soil. The longer soil is exposed at Earth’s surface, the more beryllium-10 it accumulates. Measuring how much is in soil or a rock gives geologists a kind of exposure clock.
The researchers expected to only find soil eroded from glacier-scoured bedrock in the sediment at the bottom of the ice core. But the silt they did find had very high concentrations of beryllium-10 when the team measured it on a particle accelerator at Lawrence Livermore National Laboratory, in Livermore, Calif.
“On a global basis, we only find these sorts of beryllium concentrations in soils that have developed over hundreds of thousands to millions of years,” said co-author Joseph Graly, who analyzed the beryllium data while at the University of Vermont, Burlington, Vt.
The new research, supported by funding from the National Science Foundation, shows that the soil had been stable and exposed at the surface for somewhere between 200,000 and one million years before being covered by ice.
To help interpret these unexpected findings, the team also measured nitrogen and carbon that could have been left by plant material in the core sample. “The fact that measurable amounts of organic material were found in the silty ice indicates that soil must have been present under the ice,” said co-author Andrea Lini at the University of Vermont. The composition of the material suggested that the pre-glacial landscape may have been a partially forested tundra.
“Greenland really was green! However, it was millions of years ago,” said Rood. “Before it was covered by the second largest body of ice on Earth, Greenland looked like the green Alaskan tundra.” To confirm their findings about this ancient landscape, the researchers also measured beryllium levels in a modern permafrost tundra soil on the North Slope of Alaska and found that the values were very similar.
With an eye toward better understanding its future behavior, many geologists are seeking a long-term view of the history of the Greenland Ice Sheet, including how it moves and has shaped the landscape beneath it. Its 656,000 square miles of ice contain enough water, if fully melted, to raise global sea levels twenty-three feet. “Yet, we have very little information about what is happening at the bed with regards to erosion and landscape formation,” said Corbett.
What is clear, however, from an abundance of worldwide indicators, is that global temperatures are on a path to be “far warmer than the warmest interglacials in millions of years,” said Bierman. “There is a 2.7-million-year-old soil sitting under Greenland. The ice sheet on top of it has not disappeared in the time in which humans became a species. But if we keep on our current trajectory, the ice sheet will not survive. And once you clear it off, it’s really hard to put it back on.”
Header Image : Joshua Brown, University of Vermont
Contributing Source : NASA/Goddard Space Flight Center
Durham, NC — Ancient DNA adds a twist to the story of how barnyard chickens came to be, finds a study to be published April 21 in the journal Proceedings of the National Academy of Sciences.
Analyzing DNA from the bones of chickens that lived 200-2300 years ago in Europe, researchers report that just a few hundred years ago domestic chickens may have looked far different from the chickens we know today.
The results suggest that some of the traits we associate with modern domestic chickens — such as their yellowish skin — only became widespread in the last 500 years, much more recently than previously thought.
“It’s a blink of an eye from an evolutionary perspective,” said co-author Greger Larson at Durham University in the United Kingdom.
The study is part of a larger field of research that aims to understand when, where and how humans turned wild plants and animals into the crops, pets and livestock we know today.
Generally, any mutations that are widespread in domestic plants and animals but absent from their wild relatives are assumed to have played a key role in the process, spreading as people and their livestock moved across the globe. But a growing number of ancient DNA studies tell a different tale.
Chickens are descended from a wild bird called the Red Junglefowl that humans started raising roughly 4,000-5,000 years ago in South Asia. To pinpoint the genetic changes that transformed this shy, wild bird into the chickens we know today, researchers analyzed DNA from the skeletal remains of 81 chickens retrieved from a dozen archeological sites across Europe dating from 200 to 2,300 years old.
The researchers focused on two genes known to differ between domestic chickens and their wild counterparts: a gene associated with yellow skin color, called BCDO2, and a gene involved in thyroid hormone production, called TSHR.
Though the exact function of TSHR is unknown, it may be linked to the domestic chicken’s ability to lay eggs year-round – a trait that Red Junglefowl and other wild birds don’t have.
When the team compared the ancient sequences to the DNA of modern chickens, only one of the ancient chickens had the yellow skin so common in chickens today. Similarly, less than half of the ancient chickens had the version of the TSHR gene found worldwide in modern chickens.
The results suggest that these traits only became widespread within the last 500 years — thousands of years after the first barnyard chickens came to be. “Just because a plant or animal trait is common today doesn’t mean that it was bred into them from the beginning,” Larson said.
“It demonstrates that the pets and livestock we know today — dogs, chickens, horses, cows — are probably radically different from the ones our great-great-grandparents knew,” he added.
“…They are subjected to the whim of human fancy and control, [so] radical change in the way they look can be achieved in very few generations.”
The study is part of a collection of articles in a special edition of PNAS devoted to domestication. This study and others featured in the special issue stemmed from a meeting that took place in 2011 at the National Evolutionary Synthesis Center in Durham, North Carolina. Learn more about the meeting – titled “Domestication as an Evolutionary Phenomenon: Expanding the Synthesis” — at http://domestication.groupsite.com/main/summary.
Contributing Source : National Evolutionary Synthesis Center (NESCent)
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