Scientists have decoded 2mn-year-old DNA preserved in Ice Age sediments in the far north of Greenland, revealing an ecosystem twice the age of the oldest genetic material previously discovered.
The DNA fragments, found by an international team led by researchers from Copenhagen and Cambridge universities, are from plants and animals including mastodons, reindeer, hares, birch and cedar trees thriving in what is now a polar desert.
The study, reported in the journal Nature, is the most striking demonstration so far of environmental DNA, or eDNA. This technique uses genes from multiple species taken from the surrounding environment rather than from the bones of individual specimens. They offer scientists clues as to how ecosystems adjust to climate change.
Prior to this, the oldest DNA material came from the tooth of a 1mn-year-old Siberian mammoth.
“A new chapter spanning one million extra years of history has finally been opened and for the first time we can look directly at the DNA of a past ecosystem that far back in time,” said project co-leader Eske Willerslev, a professor at both universities. “DNA can degrade quickly but we’ve shown that under the right circumstances we can now go back further in time than anyone could have dared imagine.”
The DNA samples were preserved in clay and quartz minerals within sediments at Kap København on the north-east corner of Greenland close to the North Pole. Today the area is almost lifeless but the study shows that 2mn years ago, during a warm spell between ice ages, average minimum temperatures were 10C in summer and minus 17C in winter — more than 10C higher than now.
The ecosystem has no modern analogue, combining flora and fauna characteristic of Arctic and more temperate regions. One surprise was the presence of mastodons, extinct elephantine mammals that lived mainly in North America and were not previously known to have wandered as far as Greenland.
The 40-member research team first showed that DNA fragments survived in the minerals and then extracted them to compare with genetic libraries of present-day animals, plants and micro-organisms, while guarding against contamination from modern DNA. Most were recognisable as coming from ancestors of today’s species, though many are extinct.
The samples were collected over a series of visits to Kap København going back to 2006 and then stored. “It wasn’t until a new generation of DNA extraction and sequencing equipment was developed that we’ve been able to locate and identify extremely small and damaged fragments of DNA in the sediment samples,” said Kurt Kjaer, the study’s other co-leader.
Mikkel Pedersen, a member of the research team, said the findings were relevant to global warming, which climatologists expect to occur fastest in the Arctic.
“The data suggests that more species can evolve and adapt to wildly varying temperatures than previously thought,” he said. “But, crucially, these results show they need time to do this. The speed of today’s global warming means organisms and species do not have that time so the climate emergency remains a huge threat to biodiversity and the world.”
Although DNA survives best in cold, dry conditions, the researchers hope to apply their discovery to extract genetic material from mineral grains in warmer conditions far further south. Asked how long it could survive, Willerslev said he would not be surprised if 4mn-year-old DNA were discovered in future.