Oldest Known DNA Found in Greenland Ice Core
for National Geographic News
|July 5, 2007|
The oldest known strands of DNA have been recovered from frozen mud taken from the base of Greenland's ice sheet, according to a new study.
The discovery could rewrite what was thought about Greenland's ecological past—and could alter current predictions about how global warming will affect the island's ice.
Today most of the Danish-owned island is covered with an ice sheet up to two miles (three kilometers) thick.
But the newfound DNA—genetic material from pine trees, butterflies, and other organisms that lived as much as 800,000 years ago—tells a story of a much greener and vibrant past.
Hundreds of thousands of years ago southern Greenland had thriving forests similar to those in northern Canada today, says an international team of 30 scientists led by Eske Willerslev of the University of Copenhagen in Denmark.
(See a map of Canada showing its position relative to Greenland.)
The find surpasses the previous record for the oldest DNA, which came from mammoths and other animals frozen in Siberia about 300,000 to 400,000 years ago.
The study also implies that Greenland's ice sheet did not melt as much as computer models have predicted during a period 125,000 years ago, when Earth's sea level rose dramatically.
This raises the question of where the water actually came from.
The research is described in tomorrow's issue of the journal Science.
At a site in the center of southern Greenland, researchers drilled through the thick ice until they reached the bottom layer of frozen mud, similar to the permafrost now found across areas such as Siberia.
Using a variety of techniques, the researchers were able to put an approximate date on the frozen mud: between 450,000 and 800,000 years.
"I'm not super-surprised that DNA could last that long" in Greenland, Willerslev said. "It's pretty much ideal conditions for DNA preservation."
Today it's a frigid -4°F (-20°C) at the bottom of the ice sheet at this spot, about 300 miles (500 kilometers) north of the southern tip of the island (see a map of Greenland).
Researchers have known that Greenland had some trees in the past, since they've found fossilized trees more than two million years old on the north coast of the island.
But it has been difficult to tell what the island's full ecosystem was actually like.
"Ten percent of Earth's surface is covered with ice," Willerslev said. "We have little information about the ecosystems that were there before [these places froze over]."
By comparing the DNA they found to that of today's plants and insects, the team identified the flora and fauna that used to live in this part of Greenland.
They found a variety of trees, including spruce and pine, similar to those found in northern boreal forests across Canada and northern Eurasia.
They also found signs of a number of creatures such as beetles, spiders, and butterflies.
All this suggests that before the area froze over, it had an open forest that supported a diverse ecosystem.
While these DNA discoveries help answer questions about Greenland's past environment, they may have created a new mystery related to global warming.
Based on computer models, some researchers had thought that most of southern Greenland was ice-free about 125,000 years ago, during the last interglacial period—a gap in time between ice ages when Earth was warmer.
During this period, sea levels rose about 16 to 19 feet (5 to 6 meters).
Many researchers thought that much of this water came from the melting of the southern part of Greenland's ice sheet during this time.
Several studies have found that Greenland's ice sheet is melting today, so scientists are working to predict how much the melt might contribute to sea level rise if the world continues warming.
(Related news: "Greenland Melt May Swamp LA, Other Cities, Study Says" [April 8, 2004].)
But "then we started to date [the ice] and we found that it wasn't that young," Willerslev said.
If the island had been free of ice during the last interglacial, it would likely have supported plants and animals.
In that case, DNA from those creatures should have been found instead of the DNA from the much older forest.
The new discoveries suggest that southern Greenland has been ice-covered for at least four times longer than previously thought.
"We have firm data to state that there was ice in central and northern Greenland," said Valerie Masson-Delmotte of the Laboratory of Climate and Environmental Sciences in Saclay, France.
"The main surprise [of the new study] is the persistency of ice in southern Greenland," said Masson-Delmotte, who was not involved in the new study.
And if the region was still frozen during the last interglacial period, lead author Willerslev said, then some of that water "must have come from some melting of ice somewhere else."
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