Environmental DNA reveals ecology in Northern Greenland from 2 Ma ago

The closest land to the North Pole is Peary Land in northern Greenland. Today, much of it is a polar desert and is bare of ice, so field geology is possible during the Arctic summer. It is one of the last parts of the northern hemisphere to have been mapped in detail. The bedrock ranges in age from the Mesoproterozoic to Upper Cretaceous, although the sequence is incomplete because of tectonic events and erosion during the Phanerozoic Eon. Its complex history has made Peary Land a draw for both structural geologists and stratigraphers. Apart from glacial tills the youngest rocks are estuarine sediments deposited in the early Pleistocene, between two glacial tills. They define one of the earliest known interglacials, roughly between 1.9 and 2.1 Ma, which lasted for an estimated 20 ka. Late Pliocene (3.4 Ma) sediments from around the Arctic Ocean have yielded rich fossil fauna and flora that suggest much warmer conditions – 10°C higher than those at present – before repeated glaciation began in the Northern Hemisphere. The sediments in Peary Land are fossiliferous, plant remains indicating a cover of coniferous trees, but animal fossils are restricted to small invertebrates: the tangible palaeontology offers slim pickings as regards assessing environmental conditions and the ecosystem.

One means of exploring faunal and floral diversity is through sampling and analysing DNA buried in sediments and soils rather than in fossils – plants shed pollen while animals spread their DNA via dung and urine. This approach has met with extraordinary success in revealing megafaunas that may have been decimated by humans newly arrived in the Americas. Even more remarkable was the ability of environmental DNA from cave sediments to reveal the former presence of individual humans who once lived in the caves and thus assess their numbers and relatedness. Such penetrating genetic ‘fingerprinting’ only became possible when new techniques to extract fragments of DNA from sediments and splice them to reconstruct genomes had been developed. But to apply them to material some two million years old would be a big ask; The oldest known DNA sequence had been recovered in 2021 from the molar of a 1.1 Ma old mammoth preserved in permafrost – a near-ideal source. A large multinational team under the supervision of Eske Willerslev (currently of Cambridge University, UK) took on the challenge, despite two million years of burial being likely to have degraded genetic material to minuscule fragments absorbed on the surface of minerals (Kjær, K.H. and 38 others 2022. A 2-million-year-old ecosystem in Greenland uncovered by environmental DNA. Nature, v 612, p. 283–291; DOI: 10.1038/s41586-022-05453-y). But it transpired that quartz grains have a good chance of ‘collecting’ bits of DNA and readily yielding them to the extraction media. The results are extraordinary.

Reconstruction of an American mastodon herd by American painter of large extinct fauna Charles R. Knight

The DNA extraction turned-up signs of 70 vascular plants, including poplar, spruce and yew now typically found at much lower latitudes, alongside sedges, shrubs and birch-tree species that still grow in Greenland. The climate was substantially warmer than it is now. The fauna included elephants – probably mastodons (Mammut) but not mammoths (Mammuthus) and caribou, as well as rabbits, geese and various species of rodents. There were even signs of ants and fleas. The overall assemblage of plants has no analogue in modern vegetation, perhaps because of the absence of anthropogenic influences, such as fires, the smaller extent of glaciations, their shorter duration and less established permafrost during the early Pleistocene. The last factor could have allowed a quicker and wider spread of coniferous-deciduous woodland, found today in NE Canada. In turn this spread of vegetation would have drawn in herds of large herbivores, later mastodons being known to have been wide-ranging forest dwellers. Willerslev suggests that the study has a potential bearing on how ecosystems may respond to climate change.