World’s Oldest DNA Discovered, Revealing Ancient Arctic Forest Full of Mastodons

World’s Oldest DNA Discovered, Revealing Ancient Arctic Forest Full of Mastodons

The oldest DNA ever found has revealed a remarkable ecosystem in Greenland that dates back two million years. It even includes an unlikely explorer, the mastodon.

The DNA , that was found in sediments in the region of Peary Land, at the northernmost reaches Greenland’s farthest north, shows how life was in a warmer time in Earth’s history. The landscape, which is now a harsh polar desert, once hosted trees, caribou and mastodons. While some of the animals and plants that thrived there can now be found in Arctic environments, others are only found in warmer boreal .forests. “What we see is an ecosystem with no modern analogue,” says Eske Willerslev, an evolutionary geneticist at the University of Cambridge and senior author of the study, which was published in Nature.

Until now, the oldest DNA was found in a mammoth tooth .. The marine sands of Antarctica . contained the oldest known DNA. The ancient DNA was discovered in a fossil-rich rock formation called Kap Kobenhavn in Peary Land. It preserves sediments from both the ocean and land. Geologists previously estimated that the formation was approximately two million years old. However, it has yielded a wealth of fossils of plants and insects, but no evidence of mammals. The DNA analysis now reveals 102 different genera of plants, including 24 that have never been found fossilized in the formation, and nine animals, including horseshoe crabs, hares, geese and mastodons. Willerslev said that this was “mind-blowing” because it was the first time anyone had ever thought mastodons could be found so far north.

“It paints a picture of all that was present in that ecosystem, and that’s really amazing,” Drew Christ, a postdoctoral fellow in the University of Vermont’s Gund Institute for Environment who studies the history of Earth’s polar regions, but was not involved with the research.

Researchers used disembodied DNA fragments to reconstruct ancient Peary Land. DNA fragments are released into the environment . whenever a tree’s leaves fall, a person sheds some skin, or a bunny passes away. Most of these fragments, called environmental DNA (eDNA), degrade quickly. The DNA molecules can still bind to sediments if they are exposed to the right chemical conditions. This protects them against enzymes, according to Karina Sand (study co-author), a molecular biologist at the University of Copenhagen’s Globe Institute.

These coastal deposits show traces of plants and animals that lived two million years ago in Greenland.
Close-up of organic material in the coastal deposits. The organic layers reveal traces of the rich plant flora as well as insect fauna that lived in Kap Kobenhavn, North Greenland, two million years ago. Credit: Professor Kurt H. Kjaer

The researchers began collecting sediments from Peary Land in 2006, but it took years for the technology to catch up with their ambitions. Willerslev states that every time there were improvements in DNA extraction and sequencing technology, they tried to revisit the samples. “And we failed and we failed.” The team was unable for years to extract any usable DNA from the samples.

Finally, researchers were able to extract DNA that had been severely damaged a few years back. The researchers were then able compare the DNA fragments to the genomes of modern species. Similarities in sequences showed that some species that left behind DNA were the ancestors for modern species.

Two million years ago, the site of Kap Kobenhavn was a forested coastline where a stream flowed into an estuary. Willerslev says. The river carried DNA fragments from the land into the marine environment, where it was preserved. Researchers found evidence of horseshoe crabs, a family that lives far south today, and DNA from caribou. They also found evidence for coral, ants and fleas, as well as lemmings.

The dominant plant life in this landscape was willow and birch. These plants can be found in the southern part of Greenland. Mikkel Pedersen (a physical geographer at University of Copenhagen), co-authored the study. However, trees that were only found in temperate forests like poplar or cedar are now rare. Temperatures would have averaged between 11 and 19 degrees Celsius higher than today. But Greenland was at the same latitude as it is now–meaning this ancient landscape was bathed in 24/7 darkness for nearly half the year. Willerslev states that the survival of plant life despite prolonged periods without sunlight is proof of the power evolutionary adaptation.

The two million year old Greenland-based organisms were able to survive and have descendants such as the modern caribou that now live in Arctic conditions. Willerslev believes that studying the genetic sequences from these ancient animals could reveal ways to help Arctic species survive today’s climate change.

Researchers don’t know how long environmental DNA can remain intact in sediments. Willerslev said he wouldn’t be surprised if fragments of environmental DNA were found up to four millions years ago. Linda Armbrecht, a researcher at the Institute for Marine and Antarctic Studies in Australia, said that there could be other locations on Earth where ancient DNA could help reveal how ecosystems changed as climate fluctuated. She was not involved in the new paper by Willerslev and his collaborators. *

” Both our studies have looked for DNA in cold environments: Greenland, Antarctica.” Armbrecht said. “Looking for DNA within environments and sediments that are favorable to DNA preservation (including cold temperatures, specific mineralogy, and other factors) seems to be the key to determining how far back this DNA can be preserved .”

*Editor’s Note (12/7/22): This sentence was edited after posting to correct Linda Armbrecht’s current affiliation.

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    Stephanie Pappas is a freelance science journalist. She is based in Denver, Colo.

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