Paradise found: Oldest known DNA offers glimpse of a once-lush Arctic

NEW YORK: In the permafrost at the northern edge of Greenland, scientists have discovered the oldest known fragments of DNA, offering an extraordinary look at an extraordinary ancient ecosystem.

The genetic material dates back at least two million years — that’s nearly twice as old as the mammoth DNA in Siberia that held the previous record.

And the samples, described on Wednesday in the journal Nature, came from more than 135 different species.

Together, they show that a region just 600 miles from the North Pole was once covered by a forest of poplar and birch trees inhabited by mastodons.

The forests were also home to caribou and Arctic hares. And the warm coastal waters were filled with horseshoe crabs, a species that today cannot be found any farther north of Maine. Independent experts hailed the study as a major advance.

“It feels almost magical to be able to infer such a complete picture of an ancient ecosystem from tiny fragments of preserved DNA,” said Beth Shapiro, a paleogeneticist at the University of California, Santa Cruz.

“I think it’s going to blow people’s minds,” said Andrew Christ, a geoscientist at the University of Vermont who studies the ancient Arctic. “It certainly did so for me.”

The discovery came after two decades of scientific gambles and frustrating setbacks.

One of the leaders of the project, Eske Willerslev, pioneered methods for pulling DNA out of sediment while he was a graduate student at the University of Copenhagen.

In 2003, studying a chunk of Siberian permafrost, he and his colleagues found DNA from plants such as willow and daisies dating 400,000 years ago.

That discovery set a record for the oldest DNA, and many scientists doubted it would be possible to find anything much older.

But in 2006, Dr. Willerslev and Kurt Kjaer, a geoscientist at the University of Copenhagen, tried to defy the odds in northern Greenland.

They made their way to a geological formation called Kap Kobenhavn, a series of bare hills as desolate as a moonscape. Previously, scientists had found plant fossils there that they estimated to be 2.4 million years old. Finding DNA in the sediments would have been astonishing. “If you want to move things forward, you need to take some leaps,” Dr. Kjaer said

The researchers dug up permafrost and brought it back to Copenhagen to search for DNA. They failed to find any.

In later years, Dr. Willerslev and his colleagues had more success when they examined younger sediments and bones from other parts of the world. They discovered a wealth of ancient human DNA that has helped reshape our understanding of our species’ history. Along the way, the researchers tweaked their methods for extracting DNA from ancient samples and upgraded the machines they used to sequence it. As they became better at fishing for genes, they would take out more of the Kap Kobenhavn samples for another shot.

But for years they failed, again and again. From time to time they were tantalized by what looked like short bits of DNA, which are called reads.

The researchers couldn’t rule out the possibility that bits of young DNA in Greenland, or even in their lab, had contaminated the reads.