Scientists Study Oldest-known DNA

（单词翻译）

Scientists Study Oldest-known DNA¹

Scientists discovered the oldest known DNA and used it to study what life was like 2 million years ago in Greenland.

Today, northern Greenland is an empty, cold area. But in the past, it was full of trees, plants, and animals.

Kurt Kjaer of the University of Copenhagen was the study's lead writer. He said the research "opens the door into a past that has basically been lost."

For the study, researchers examined environmental DNA, also known as eDNA, from soil samples. eDNA is the genetic² material that organisms put into their surroundings, including hair and waste.

The problem with ancient DNA is that the genetic material breaks down over time, leaving scientists with very small pieces to study. But, with the latest technology, Eske Willerslev of the University of Cambridge said researchers were able to get genetic information out of the small, damaged pieces of DNA.

In the study, which appeared recently in the publication Nature, researchers compared the DNA to that of different species, looking for matches.

The samples came from an area in Peary Land, which is now a cold, empty place. But millions of years ago, the area went through a time of strong climate change that sent temperatures way up, Willerslev said.

Soil and rocks likely built up for tens of thousands of years in the area before the climate cooled and locked the DNA into permafrost. The cold environment helped save the small pieces of DNA — until scientists came along and took the samples out, beginning in 2006.

The researchers said when average temperatures were 11 to 19 degrees Celsius³ higher than today, the area had an unusual number of plant and animal life. And pieces of DNA suggest a mix of Arctic plants with ones that usually grow in warmer climates.

The DNA also showed the presence of animals including geese, hares, reindeer⁴ and lemmings. Previously⁵, a dung beetle⁶ and some hare remains⁷ had been the only signs of animal life in the area, Willerslev said.

The researchers said one big surprise was finding DNA from the mastodon, an ancient species that looked like a mix between an elephant and a mammoth⁸. Mastodon DNA remains have previously been found in forests in North America, a long way away from Greenland.

"I wouldn't have, in a million years, expected to find mastodons in northern Greenland," said Love Dalen. Dalen, who was not involved in the study, is a researcher at Stockholm University.

DNA samples also suggest the presence of horseshoe crabs⁹ and green algae¹⁰ in the area. Kjaer explained that nearby waters were likely much warmer back then.

Laura Epp, who was not involved in the study, is an eDNA expert at Germany's University of Konstanz. She said, with the available data, it is hard to say for sure whether these species lived side by side, or if the DNA was mixed together from different parts of the landscape. But Epp said this kind of DNA research is valuable to show "hidden diversity" in ancient landscapes.

Willerslev believes that because these plants and animals survived during a time of extreme climate change, their DNA could offer a "genetic roadmap" to help us deal with current warming.

Stockholm University's Dalen expects ancient DNA research to keep pushing deeper into the past.

"I wouldn't be surprised if you can go at least one or perhaps a few million years further back, assuming you can find the right samples," Dalen said.

Words in This Story

DNA – n. a substance that carries genetic information in the cells of plants and animals — often used before another noun

basically -- adv. in a general or basic way — used to say that something is true or correct as a general statement even if it is not entirely¹¹ true or correct

sample – n. a small amount of something that gives you information about the thing it was taken from

species -- n. biology : a group of animals or plants that are similar and can produce young animals or plants : a group of related animals or plants that is smaller than a genus

permafrost – n. a layer of soil that is always frozen in very cold regions of the world

mammoth – n. a type of large, hairy elephant that lived in ancient times and that had very long tusks¹² that curved upward

landscape -- n. an area of land that has a particular quality or appearance

assume -- v. to think that something is true or probably true without knowing that it is true