DNA bound to mineral particles in ancient sediment reveals that north Greenland once had spruce forests populated by hares, reindeer and even mastodons
DNA from 2 million years ago recovered from sediments in Greenland is the oldest preserved DNA found to date, blowing past the previous benchmark of 1 million years set in 2021.
“The age of the DNA is twice as old approximately compared to what has been retrieved previously,” says Eske Willerslev at the University of Cambridge.
The DNA comes from a host of different organisms, enabling Willerslev and his colleagues to reconstruct the ecosystem that existed in northern Greenland 2 million years ago, at a time when the climate was warmer than it is today. Today, the area is Arctic desert and has few organisms, but back then it was a forest inhabited by hares, reindeer and perhaps even mastodons, elephant-like animals that once lived in North America.
The find suggests that it will be possible to uncover DNA from much more ancient time periods than previously suspected. “I wouldn’t be surprised if it turned out that in the north [the Arctic], we could go twice as far back in time,” says Willerslev.
He and his team obtained ancient DNA from the Kap København Formation, a series of layers of sand, silt and mud more than 90 metres thick in total. These were laid down 2 million years ago.
The DNA didn’t come from fossilised organisms, but was instead bound to mineral particles in the sediment layers. This helped preserve the DNA, because enzymes couldn’t get to it to break it down, says team member Karina Sand at the University of Copenhagen in Denmark.
This environmental DNA came from the whole range of organisms living in the area. The team detected 102 genera of plants. Some still grow in northern Greenland today, like the shrubs Dryas and Vaccinium. But others no longer live there, like spruce (Picea) trees, hawthorn (Crataegus) and Populus flowers. “It is, in fact, a forest,” says Willerslev.
Fewer animal species were identified, probably because they always make up less of the biomass than plants, says Willerslev. Nevertheless, the DNA revealed Arctic hares (Lepus arcticus), rodents related to lemmings and muskrats, geese and reindeer.
There was also DNA from an extinct elephant relative, which the team tentatively identified as a mastodon, not a mammoth. Mastodons lived in the Americas for several million years, but hadn’t previously been found in Greenland. It isn’t known how mastodons might have travelled to Greenland, but they may have crossed sea ice.
If free-floating DNA can survive this long by binding to mineral particles in cold conditions, it suggests there is truly ancient DNA to be found, says Laura Parducci at Sapienza University of Rome in Italy, who wasn’t involved in the research.
The Kap København Formation existed early in the Pleistocene Epoch, which began 2.58 million years ago and ended 11,700 years ago. At the start of the Pleistocene, permanent ice covered the north pole for the first time in millions of years, and it has remained frozen ever since. Furthermore, the Arctic was cold even before the Pleistocene, so there might be some permafrost that is even older – with DNA preserved in it.
However, Antarctica froze over much earlier, beginning around 35 million years ago, says Parducci. “So potentially there you can go much deeper in time.” However, “the diversity of the plants and animals would be far less”, says Kurt Kjaer at the University of Copenhagen, one of the study authors, because Antarctica has been polar desert for so long.
Journal reference: Nature, DOI: 10.1038/s41586-022-05453-y
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