The world's oldest DNA represents a two-million-year-old ecosystem

A window has been opened into a unique ecosystem that once existed in northern Greenland.

Sediment samples taken from the geological formation Kap København contained minute DNA fragments, dating back two million years into the Pliocene.  Researchers sequenced them to identify the animals and plants that once inhabited the area. 

Forests of willow and birch trees would have supported herbivores that would be recognisable today, such as hares and deer, as well as extinct species such as the mastodon. 

These species thrived in the Arctic in a time where temperatures were as much as 19⁰C warmer than today. Researchers hope their findings will provide insight into how modern plants and animals could adapt to rising temperatures, and how humanity can assist in this transition. 

Professor Mikkel W. Pedersen, who is one of the lead authors of the study published in Nature, says, 'The Kap København ecosystem was a mix of Arctic and temperate species, and has no present-day equivalent. It existed at considerably higher temperatures than we have today, and its climate seems to have been similar to that we expect on our planet in the future due to global warming.'

'While our research suggests that more species can evolve and adapt to wildly varying temperatures than previously thought, they crucially 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.' 

What is Kap København?

Today, Kap København is one of Greenland's northern extremities, sticking out into the Arctic Ocean at the end of Independence Fjord. Like much of the island, it is covered in snow and ice, but beneath the surface it is very different. 

The study's other lead author, Professor Eske Willerslev, describes the site as a 'polar Sahara'.

'There is almost no life of any significance here now,' Eske says. 'But two million years ago, it would have been a forest teeming with life surrounding a river running into the bay.'

What appear to be piles of icy debris, known as moraines, are actually the remnants of these river and ocean sediments. Researchers have dated these sediments to between 1.9 and 2.1 million years old.

The site was discovered in 1979, with the first major investigation four years later turning up cones, needles and twigs from long dead conifer trees which are thought to have been washed into the sea before burial. Subsequent discoveries have included fossilised ants and other species that cannot tolerate the conditions of Greenland today.

While fossil remains and preserved pollen found at Kap København have helped to build a picture of how the site would have been in the past, traces of vertebrates were uncommon. Researchers had estimated that small fragments of DNA could have survived, based on fossils found elsewhere, but attempts to sequence it had been unsuccessful.

Recent advances in DNA sequencing technology allowed minute environmental DNA (eDNA) fragments contained in clay sediments to be sequenced for the first time, revealing a host of new wildlife that weren't previously known.

Most surprising is the presence of the mastodon, an extinct elephant-like animal which was previously only known of from continental North America. It is possible they may have crossed over ice sheets that no longer exist between the continent and Greenland, or perhaps they even swam.

To support such a large herbivore, and others such as caribou, Kap København must have been rich in plant life. In addition to 78 plant genera already identified from the site, the researchers detected another 24 from eDNA, including poplar trees and a variety of herbaceous plants that could have provided nourishment.

No carnivores were found at the site, but it's reasonable to assume that they were present.

'It is most likely that there were carnivores at the site, but we didn't find any and this is probably because predatory animals are rarer in food chains,' Eske explains. 'The eDNA reflects the biomass of the ecosystem, so plant DNA is the most common overall, while herbivores are the most common animals.'

'I predict that further sequencing could uncover the DNA of carnivorous animals.' 

Looking to the future of eDNA

Following the success of sequencing animal and plant DNA at Kap København, the researchers are writing a paper on the microbial life of the site and hope to search for similar sites elsewhere.

One promising site is in Canada, where permafrost may help to preserve even older DNA. The team plans to take samples from this site in the coming year.

However, the technique may also have applications outside of the world's coldest areas, depending on the minerals that are found there.

Co-author Professor Karina Sand says, 'Minerals can adsorb DNA, where it forms a surface layer, and different minerals bond at different strengths. We found that clay minerals bind particularly strongly to DNA, which gave us difficulties in separating them.'

'The same bonds we found difficult to separate can also help to preserve DNA. While the mechanisms are not well-understood, it may help prevent enzymes accessing the DNA to degrade it.'

Clay deposits at warmer sites could contain similar eDNA deposits, which could help to unpick some of evolution's biggest questions. 

'While nobody knows if this technique can be used in warmer environments, DNA clearly acts differently in sediments as opposed to when it is in solution,' Eske says. 'Now that we have successfully extracted ancient DNA from clay and quartz, it may be possible that clay may have preserved ancient DNA in warm, humid environments in sites found in Africa.'

'If we can begin to explore ancient DNA in clay grains from Africa, we may be able to gather ground-breaking information about the origin of many different species, and perhaps even new knowledge about early Homo sapiens and their relatives.'