NEW YORK — Scientists discovered the oldest known DNA and used it to reveal what life was like 2 million years ago in the northernmost tip of Greenland. Today it is a barren Arctic desert, but then it was a lush landscape of trees and vegetation that was home to an array of animals, even the now-extinct mastodon.
“The study opens the door to a past that has actually been lost,” said lead author Kurt Kjær, a geologist and glacier expert at the University of Copenhagen.
Because animal fossils were hard to come by, the researchers extracted environmental DNA, also known as eDNA, from soil samples. This is the genetic material that organisms release into their environment, for example through hair, waste, saliva or decomposing carcasses.
Studying really ancient DNA can be challenging because the genetic material breaks down over time, leaving scientists with only tiny fragments.
But with the latest technology, researchers were able to extract genetic information from the small, damaged bits of DNA, explains senior author Eske Willerslev, a geneticist at the University of Cambridge. In their study, published Wednesday in the journal Nature, they compared DNA with that of different species, looking for similarities.
The samples came from a sediment deposit called the Kap København Formation in Peary Land. Today, the area is a polar desert, Kjær said.
But millions of years ago, this region underwent a period of intense climate change that sent temperatures soaring, Willerslev said. Sediment probably built up at the site over tens of thousands of years before the climate cooled and cemented the finds in permafrost.
The cold environment would help preserve the delicate bits of DNA — until scientists came along and drilled out the samples, beginning in 2006.
During the region’s warm spell, when average temperatures were 20 to 34 degrees Fahrenheit (11 to 19 degrees Celsius) higher than today, the area was filled with an unusual array of plant and animal life, the researchers reported. The DNA fragments suggest a mix of Arctic plants, such as birch trees and willow shrubs, with plants that usually prefer warmer climates, such as spruce and cedar.
The DNA also showed traces of animals, including geese, hares, reindeer and lemmings. Previously, a dung beetle and some hare remains were the only signs of animal life at the site, Willerslev said.
A big surprise was finding DNA from the mastodon, an extinct species that looks like a mix between an elephant and a mammoth, Kjær said.
Many mastodon fossils have previously been found in temperate forests in North America. That’s an ocean away from Greenland, and much further south, Willerslev said.
“I never expected in a million years to find mastodons in northern Greenland,” said Love Dalen, a researcher in evolutionary genomics at Stockholm University, who was not involved in the study.
Because the sediment accumulated in the mouth of a fjord, researchers were also able to get clues about marine life from this period. The DNA suggests horseshoe crabs and green algae lived in the area — meaning the nearby waters were likely much warmer back then, Kjær said.
By extracting dozens of species from just a few sediment samples, the study highlights some of the benefits of eDNA, said Benjamin Vernot, a longtime DNA researcher at Germany’s Max Planck Institute for Evolutionary Anthropology who was not involved in the study.
“You really get a broader view of the ecosystem at a point in time,” Vernot said. “You don’t have to go find this piece of wood to study this plant, and this bone to study this mammoth.”
Based on the available data, it’s hard to say for sure whether these species actually coexisted, or whether the DNA from different parts of the landscape was mixed up, said Laura Epp, an eDNA expert at Germany’s University of Konstanz who does not was involved in the study.
But Epp said this kind of DNA research is valuable for showing “hidden diversity” in ancient landscapes.
Willerslev believes that because these plants and animals survived during a time of dramatic climate change, their DNA could provide a “genetic roadmap” to help us adapt to the current warming.
Dalen from Stockholm University expects ancient DNA research to penetrate deeper and deeper into the past. He was working on the study that previously contained the “oldest DNA” record, of a mammoth tooth about a million years old.
“I wouldn’t be surprised if you can go back at least one or maybe a few million years further back, assuming you can find the right samples,” Dalen said.
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