Not much lives in the northernmost tip of Greenland today. Some lichens and moss survive in the polar desert, but “almost nothing there of any life, of any significance,” said evolutionary geneticist Eske Willerslev. Yet millions of years ago, a much warmer climate supported an ecosystem that was teeming with a wide diversity of life — and Willerslev has the DNA to prove it.
In a study published Wednesday in Nature, Willerslev and his colleagues genetically mapped 2-million-year-old DNA from Arctic sediments — now the world’s oldest DNA to be identified. They discovered evidence of more than 100 plant genera, nine animal taxa including the extinct elephant-like mastodon, and even marine life within the same region.
The findings could help researchers understand what to expect in a warmer future. Previous paleoclimatic records show the ancient ecosystem was 10 to 17 degrees Celsius (18 to 31 degrees Fahrenheit) warmer than modern-day Greenland. The DNA evidence could provide researchers clues on how these life-forms survived under extreme temperatures.
“It’s actually the climate which is very similar to what we expect to face on Earth due to global warming,” said Willerslev, a professor at the University of Cambridge. “It gives us some kind of idea [or] impression of how … can nature respond to increasing temperatures.”
The discovery took a lot of patience and detective work over 16 years. Co-author Kurt Kjaer said many of the samples were collected in 2006 from the Kap Kobenhavn Formation, a 100-meter-thick sediment deposit at the mouth of a fjord in Greenland’s northernmost point. The DNA samples were well preserved in sediment and ice, undisturbed by humans for 2 million years. At the time of collection, though, technology was not advanced enough to extract the microscopic, fragmented genetic material from the clay and quartz sediments. So the team stored them.
Over the years, researchers attempted to extract the samples but to no avail. Some even left academia after working on them, which led lab members to joke it was the “the curse of the Kap Kobenhavn Formation.”
So paleoecologist Mikkel Pedersen wasn’t exactly ecstatic when Kjaer handed him the DNA-laden sediments. “I’ve seen the other people working on it who, after working on it, left academia. … So I didn’t feel very good,” said Pedersen at the University of Copenhagen.
But Pedersen made use of a new generation of DNA extraction and sequencing that could locate and identify the damaged DNA fragments, which measured only a few millionths of a millimeter long. A team effort painstakingly matched every fragment with extensive libraries of DNA collected from present-day plants, animals and organisms.
“I got all these different plants and animals, but then suddenly I got marine species,” Pedersen said. “This was kind of a little bit crazy to me.”
Soon, a picture of the ancient forests, bays, flora and fauna came into focus. Yet the results were also puzzling — many of the uncovered animals and plants didn’t seem to make ecological sense. Plants and animals that are typically found in the Arctic were in the same ecosystem as those found in boreal forests further south. One abundant plant genus was dryas, which is typically found in the Arctic. Yet the team also found poplars, deciduous trees usually found in boreal forests.
Perhaps the most surprising discovery was the mastodon, a hairy relative of the elephant that has long been associated with boreal forests in North America. Willerslev said no one had speculated the mammal would travel so far north, but maybe it traveled across the ice with the reindeer.
Additionally, the team found evidence for hares, rodents, geese and lemmings. The presence of horseshoe crabs and blue algae also indicates a warmer regional climate than today.
“The two things that stand out to me are how old and diverse the analyzed DNA is,” said Matthew Barnes, an ecologist at Texas Tech University who was not involved in the research, in an email. “It’s a mishmash of species that ‘do’ and ‘don’t’ belong together based on our understanding of modern ecology.”
The most exciting aspect to Barnes was the team’s ability to learn about a whole ancient community, rather than a targeted analysis of preserved tissue or feces. Previously, the oldest known recovered DNA was 1 million years old and came from a permafrost-preserved Siberian mammoth tooth, which provided limited information on the surrounding environment. Analyses of environmental DNA, such as in this study, paint a more comprehensive picture of organisms that were living together in a certain place and time.
Overall, Willerslev said the findings show that organisms are much more adaptable and “complex than what we imagined.” He said the DNA information could be used as a “genetic road map” for engineering plants, for example, to make them more resilient in the face of climate change. Some flora and fauna adapted to the high heat 2 million years ago, he said, and their descendants may have lost that ability as Earth cooled — but we can still learn from them today.
“We have a genetic road map of how do taxa adapt to climatic changes to a warmer climate,” Willerslev said. “If we manage to read this road map correctly, it really contains the key to how can we help organisms adapt to a very fast-changing climate, both in terms of organism compositions, which organisms can actually be together ... but, of course, also in terms of genetic adaptations.”