The oldest DNA remains reveal that Greenland was an orchard two million years ago

by time news

Under the direction of Eske Willerslev y Kurt H. Kjær, from the Universities of Cambridge and Copenhagen, an international team of more than 40 researchers has just identified, for the first time, environmental DNA (that is, not from fossil remains, but from the ground itself) two million years old, a milestone that will completely change the way we understand and describe the history of evolution.

The small pieces of DNA appeared in Ice Age sediments in northern Greenland, and the scientists were able to verify that they are up to a million years older than DNA previously found in the same region but obtained from a Siberian mammoth bone. .

With this treasure in their hands, Willerslev, Kjær and the rest of the team managed to reconstruct an entire ecosystem from two million years ago, one that was capable of withstanding extreme climate change. In total, 41 useful samples were analyzed and their analysis has just been published in ‘Nature’.

“Finally,” says Kjær, “a new chapter spanning an additional million years of history has been opened and, for the first time, we can look directly at the DNA of an ecosystem passed so far back in time… DNA can degrade rapidly, but we have It has shown that, under the right circumstances, we can now go further back in time than anyone could have dared to imagine.”

Kjær explains that the DNA samples were found buried deep in a sediment that, two million years ago, had accumulated little by little for at least 20,000 years: “the sediment,” he says, “was eventually preserved in ice or permafrost and, more importantly, humans did not disturb it for two million years.”

All samples, just a few millionths of a millimeter long, were obtained at the Formation Copenhagen, a sediment deposit almost 100 meters thick hidden at the mouth of a fjord in the Arctic Ocean, at the northernmost point of Greenland. The climate there at that time varied between arctic and temperate and temperatures ranged between 10 and 17 degrees Celsius, that is, much higher than today.

Researchers take sediment samples for environmental DNA in Greenland

Courtesy of NOVA, HHMI Tangled Bank Studios, and Handful of Films

Although small and incomplete, the DNA samples concealed a veritable treasure trove of information. In them, in effect, the researchers discovered evidence of animals, plants and microorganisms, including reindeer, hares, lemmings, birch trees and poplars. The researchers even found that mastodons, an Ice Age mammal, made their way as far as Greenland before going extinct a little later. It was previously thought that the range of the elephant-like animals did not extend as far as Greenland from their known origins in North and Central America.

A detective work

The analysis work, a true detective work, was carried out by 40 researchers from Denmark, the United Kingdom, France, Sweden, Norway, the United States and Germany, and managed to reveal all the secrets hidden in the DNA fragments. The process was laborious: first it was necessary to establish whether there was indeed DNA hidden in the clay and quartz. And if there was, would it be possible to successfully separate it from the sediment for examination? The answer, finally, was a resounding yes.

The researchers compared each fragment with extensive DNA libraries collected from living animals, plants, and microorganisms. Thus began to emerge the image of a landscape populated by trees, shrubs, birds, animals and microorganisms of all kinds. Some of the fragments were easy to classify as ancestors of current species, others could only be linked at the genus level, and some belonged to species that were impossible to locate in the DNA libraries of animals, plants, and microorganisms still living in the 21st century. .

an unknown stage

The two-million-year-old samples also help scholars build a picture of a previously unknown stage in the evolution of the DNA of a variety of species that still exist today. In Kjær’s words: “The expeditions are expensive and many of the samples were taken in 2006, when the team was in Greenland for another project. They have been in storage ever since. In fact, it was not until a new generation of DNA extraction and sequencing equipment was developed that we were able to locate and identify extremely small and damaged DNA fragments in sediment samples. And that meant we could finally map an ecosystem from two million years ago.”

Eske Willerslev prepares samples in Copenhagen

Courtesy of NOVA, HHMI Tangled Bank Studios, and Handful of Films

The work will also be very useful to find out which species are capable of surviving major climate changes, but above all it opens a new era in the study of extinct species and ecosystems. As Willerslev explains. “DNA generally survives best in cool, dry conditions, such as have prevailed for most of the period since the material was deposited in Cape Copenhagen. Now that we have successfully extracted ancient DNA from clay and quartz, we believe that clay may have preserved ancient DNA also in hot and humid environments at sites found in Africa.”

Therefore, if it were possible to recover ancient DNA in clay grains from Africa, “we will be able to collect innovative information about the origin of many different species, perhaps even new knowledge about the first humans and their ancestors. The possibilities are endless”.

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