The world’s oldest DNA: Scientists find 2 million-year-old remains of plants and animals
In recent years, research into ancient DNA has accelerated. Scientists have managed to extract DNA from old bones, from soil in caves and the bottom of lakes.
The remains of the genetic material can tell about nature and people In the past.
In 2021, researchers reported about the discovery of the world’s oldest DNA. It came from mammoths that lived around a million years ago.
Well, a Danish-led research group has uncovered DNA from Greenland that is approximately twice as old. The study is published in the journal Nature.
Hereditary material from the elephant mastodon, thuja, birch, reindeer, geese and much more tells about the ecosystem in Greenland in the first part of the Quaternary, the period which includes the ice ages.
Researchers at UiT Norway’s Arctic University have participated in studies.
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Pushing the limits
– DNA can be broken down quickly, but we have shown that under the right circumstances we can go back in time and someone could have dared to imagine, says Professor Eske Willerslev in a press release.
Among other things, he is director of the Lundbeck Foundation GeoGenetics Center at the University of Copenhagen.
This time, the researchers did not retrieve DNA from bones, but from sediments.
Sediments are loose masses that have accumulated on land or at the bottom of water. It can consist of bits and particles of rock, soil or biological material.
A warmer Greenland
The researchers analyzed 41 samples. They are taken from a hundred-metre-thick assemblage of sediments at the mouth of a fjord in the north of Greenland. The square is called Cape Copenhagen.
The sediments had built up over 20,000 years during an intermediate period approximately millions of years ago. At that time it was over ten degrees warmer in Greenland than today.
For the past 2.6 million years, the earth has gone in and out of periods, replaced by shorter, warmer interglacial periods.
– The sediment was finally preserved in the permafrost and, decidedly, not disturbed by humans for millions of years, says Professor Kurt H. Kjær at the Lundbeck Foundation GeoGenetics Centre, who was also involved in the studies.
Was it a forest there?
In the samples, the researchers found fragments of DNA from an ecosystem in Greenland that was different from today’s. It was a greener and warmer island.
Today, approximately 81 percent of Greenland is covered throughout the year, according to Great Norwegian Lexicon.
Two million years ago, several types of trees grew on the island, the DNA analysis showed.
– We have discussed a lot whether it was the forest or just scattered trees, says Inger Greve Alsos.
She is a professor of biology at UiT Norway’s Arctic University and has participated in studies.
– Based on the fact that there were so many arctic species present as well, we think it was more scattered trees and a lot of tundra landscape, Alsos tells forskning.no.
The researchers found, among other things, traces of birch, aspen and willow.
– We also found hawthorn, yew and thuja. These are not species that are generally associated with the Arctic today.
Mastodon and reindeer
Furthermore, traces of some of the animal life appeared.
It turned out that mastodons lived in Greenland at this time. It was a huge elephant animal that lived in North and Central America until it died out around 10,000 years ago.
The study shows that these Ice Age animals spread all the way up to Greenland.
The researchers also found DNA from reindeer, hare, goose and lemur. These are animals that are still found in Greenland today.
Shows the evolution of the arctic species
When it comes to plant life, Alsos says that it is a mixture of arctic species that we know from today and boreal forest. Boreal forest is the coniferous forest found in Norway, Canada and in northern areas.
For example, the researchers found meadowsweet in old Greenland. Medwort is common in Norway, but is not found in arctic areas today.
Of 102 plant genera, 39 percent no longer grow in Greenland, but are found in the forests of North America today. For example, spruce, thuja and hawthorn.
– This is the time when the cooling of the earth began. You have to remember that arctic vegetation is only about 2 to 2.5 million years old, says Alsos.
In the new study, the researchers can look back on the development of plant life when it began to be properly called in the north.
– There were cold high alpine areas like in the Himalayas, for example. The new study supports the theory that the arctic vegetation is partly from former alpine species and partly from the boreal forest.
The boreal forest stretched all the way north of Greenland before.
Progenitors
From some species, the researchers had enough material to make a genetic comparison with conifer species found in the area.
Then they found out that the species that lived there two million years ago are ancestors of today’s species.
– We see it both with the animals and the plants, says Alsos.
It is actually quite as expected, she says.
– They lived millions of years earlier, so they should be ancestors. But it is very nice to see that the genetics correspond to expectations. This applied both to the three species of birch, aspen and willow, but also with the animals we have done it on.
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– Provides insight into the ecosystems of the past
Alexandra Rouillard is a postdoctoral fellow at UiT Norway’s Arctic University at the Department of Geosciences. She has also participated in studies.
– It is to imagine that the polar desert in the high Arctic today, once had a habitat that was lush enough for such as eel island megafauna and “open forest” type plants, writes Rouillard in an e-mail to research.
It wasn’t that long ago either, considering that the tectonic plates lay in the same way as today, she points out.
– These plants and animals would still have had to survive the polar night, that is to say they were adapted to it in some way, writes Rouillard.
Anne Elisabeth Bjune is a professor at the University of Bergen and researcher at the Bjerkness Center for Climate Research. She works with past vegetation and climate history using plant remains, and has not participated in studies.
– The new environmental DNA data being presented from Greenland gives us good insight into the ecosystems of the past – for both plants and animals, from sea and land, writes Bjune in an e-mail to forskning.no.
– Both the data itself is important and also the methodological development made in this study, she continues.
Bjune writes that the data are important for reasons: They represent a time period about which we do not have very detailed knowledge, and they give us knowledge about the composition of ecosystems in a climate that is expected in the future.
Broken up into small pieces
The DNA the researchers found was damaged and broken into many small pieces after many years in the tray.
– These are very short sequences. It is as expected when it is this old, says Inger Greve Alsos.
– When you have such short sequences, you must have quite a lot of it to be sure of the identification. If not, you can get a random match.
To find out what kind of DNA is in the sample, the fragments were matched with DNA from today’s species that have had their entire genome mapped.
The reference library at UiT was important here. It is made from plants in the herbarium at Tromsø museum. The library contains over 1,500 plant genes, which have been used to identify what kind of DNA was present in the samples.
As libraries are important tools, says Alsos.
She thinks it was definitely DNA from many other organisms in the samples, such as various insects, moss and lichen.
– We have not managed to fish it out, because we do not have full genome sequences. When we say that we have uncovered an ecosystem, the main focus is still on the large vascular plants and mammals.
Preserved in clay and quartz
With such old DNA, there is a high risk of contamination. Alsos says that a strength of the study is that they found ancient pollen and fossils from many of the same genera or species from which they found DNA.
– There is a great deal of agreement. It was too much convincing that this is correct. Then, of course, you look at the pattern of damage, which shows that the DNA is old.
Good preservation conditions made it possible to find DNA from millions of years ago.
– The place is about as far north as you can get in the Arctic. Low temperature preserves DNA, says Alsos.
The researchers extracted DNA from clay, smectite and quartz in the sediments. Smectite is a group of clay minerals that swell in contact with water.
– We know that clay binds DNA very strongly. Smectite binds it even better. If the DNA is loose, microorganisms will just eat it up and it will break down. But if it is chemically bound, it is preserved better, says Alsos.
Theoretical studies on how long DNA can be preserved are based on bones, says Alsos.
Has the limit been reached?
Alexandra Rouillard thinks one of the most exciting things about the new research is the age of the DNA.
– From a technical point of view, the data can be presented in this article’s limits for what we may be able to detect using DNA going back millions of years, says Rouillard.
Will the record be broken again, or has the limit been reached for how old DNA it is possible to find?
– It is difficult to say, because we thought before that we were on the border, says Alsos.
– If it is something that really characterizes research on ancient DNA, then it is that you break the boundaries. But we are probably at the theoretical lower end of the limits for how far back you can go.
The field is only about 20 years old, says Alsos.
Regardless, it is exciting that remains to be researched from the last 2 million years.
– Within the professional environment, we don’t really have that much in such old tests. Because we have not known that it is possible to find DNA in them. The vast majority of studies of ancient DNA are less than 50,000 years old.
– I think we will now look for more places with sediments that are older and see what we can find, says Inger Greve Alsos.
Reference:
Kurt H. Kjær, m. fl.: “A 2 million-year-old ecosystem in Greenland revealed by environmental DNA”, NatureDecember 7, 2022.
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