[ti:Scientists Study Oldest-known DNA]
[by:www.21voa.com]
[00:00.00]更多听力请访问21VOA.COM
[00:00.04]Scientists discovered the oldest known DNA
[00:04.48]and used it to study what life was like 2 million years ago in Greenland.
[00:10.76]Today, northern Greenland is an empty, cold area.
[00:16.32]But in the past, it was full of trees, plants, and animals.
[00:23.00]Kurt Kjaer of the University of Copenhagen
[00:26.68]was the study's lead writer.
[00:29.28]He said the research "opens the door into a past
[00:33.36]that has basically been lost."
[00:35.84]For the study, researchers examined environmental DNA,
[00:41.36]also known as eDNA, from soil samples.
[00:46.20]eDNA is the genetic material that organisms
[00:50.76]put into their surroundings, including hair and waste.
[00:55.20]The problem with ancient DNA is that the genetic material
[00:59.76]breaks down over time,
[01:01.84]leaving scientists with very small pieces to study.
[01:06.04]But, with the latest technology,
[01:09.48]Eske Willerslev of the University of Cambridge
[01:13.36]said researchers were able to get genetic information
[01:17.80]out of the small, damaged pieces of DNA.
[01:22.88]In the study, which appeared recently in the publication Nature,
[01:27.92]researchers compared the DNA
[01:30.76]to that of different species, looking for matches.
[01:34.72]The samples came from an area in Peary Land,
[01:38.56]which is now a cold, empty place.
[01:42.04]But millions of years ago,
[01:44.36]the area went through a time of strong climate change
[01:48.16]that sent temperatures way up, Willerslev said.
[01:52.12]Soil and rocks likely built up for tens of thousands of years in the area
[01:58.52]before the climate cooled and locked the DNA into permafrost.
[02:03.68]The cold environment helped save the small pieces of DNA
[02:08.92]— until scientists came along and took the samples out, beginning in 2006.
[02:16.52]The researchers said when average temperatures
[02:19.60]were 11 to 19 degrees Celsius higher than today,
[02:24.08]the area had an unusual number of plant and animal life.
[02:28.96]And pieces of DNA suggest a mix of Arctic plants
[02:34.20]with ones that usually grow in warmer climates.
[02:37.60]The DNA also showed the presence of animals including geese,
[02:42.88]hares, reindeer and lemmings.
[02:46.52]Previously, a dung beetle and some hare remains
[02:51.28]had been the only signs of animal life in the area, Willerslev said.
[02:56.84]The researchers said one big surprise was finding DNA from the mastodon,
[03:03.24]an ancient species that looked like a mix
[03:06.40]between an elephant and a mammoth.
[03:09.96]Mastodon DNA remains have previously been found in forests
[03:15.04]in North America, a long way away from Greenland.
[03:20.32]"I wouldn't have, in a million years,
[03:22.96]expected to find mastodons in northern Greenland," said Love Dalen.
[03:28.72]Dalen, who was not involved in the study,
[03:32.44]is a researcher at Stockholm University.
[03:36.76]DNA samples also suggest the presence of horseshoe crabs
[03:41.44]and green algae in the area.
[03:44.04]Kjaer explained that nearby waters
[03:46.80]were likely much warmer back then.
[03:50.12]Laura Epp, who was not involved in the study,
[03:53.96]is an eDNA expert at Germany's University of Konstanz.
[03:59.28]She said, with the available data, it is hard to say for sure
[04:04.48]whether these species lived side by side,
[04:07.84]or if the DNA was mixed together from different parts of the landscape.
[04:14.08]But Epp said this kind of DNA research
[04:17.00]is valuable to show "hidden diversity" in ancient landscapes.
[04:22.32]Willerslev believes that because these plants and animals survived
[04:27.16]during a time of extreme climate change,
[04:30.24]their DNA could offer a "genetic roadmap"
[04:33.64]to help us deal with current warming.
[04:36.40]Stockholm University's Dalen expects ancient DNA research
[04:41.28]to keep pushing deeper into the past.
[04:45.04]"I wouldn't be surprised if you can go at least one
[04:48.60]or perhaps a few million years further back,
[04:51.72]assuming you can find the right samples," Dalen said.
[04:57.04]I'm John Russell. 更多听力请访问21VOA.COM
END OF TRACK. "END OF TRACK." The two men bowed. "Whoever was that person you were talking to?" she enquired, as soon as they stood together. The took of triumph faded from her eyes, she had grown worn and weary. The roses were wilting on the walls, the lights were mostly down now. Hetty, looking in to see if anything was wanted, found herself driven away almost fiercely. I only saw Master Jervie once when he called at tea time, The year 1747 was opened by measures of restriction. The House of Lords, offended at the publication of the proceedings of the trial of Lord Lovat, summoned the parties to their bar, committed them to prison, and refused to liberate them till they had pledged themselves not to repeat the offence, and had paid very heavy fees. The consequence of this was that the transactions of the Peers were almost entirely suppressed for nearly thirty years from this time, and we draw our knowledge of them chiefly from notes taken by Horace Walpole and Lord Chancellor Hardwicke. What is still more remarkable, the reports of the House of Commons, being taken by stealth, and on the merest sufferance, are of the most meagre kind, sometimes altogether wanting, and the speeches are given uniformly under fictitious names; for to have attributed to Pitt or Pelham their[112] speeches by name would have brought down on the printers the summary vengeance of the House. Many of the members complained bitterly of this breach of the privileges of Parliament, and of "being put into print by low fellows"; but Pelham had the sense to tolerate them, saying, "Let them alone; they make better speeches for us than we can make for ourselves." Altogether, the House of Commons exhibited the most deplorable aspect that can be conceived. The Ministry had pursued Walpole's system of buying up opponents by place, or pension, or secret service money, till there was no life left in the House. Ministers passed their measures without troubling themselves to say much in their behalf; and the opposition dwindled to Sir John Hinde Cotton, now dismissed from office, and a feeble remnant of Jacobites raised but miserable resistance. In vain the Prince of Wales and the secret instigations of Bolingbroke and Doddington stimulated the spirit of discontent; both Houses had degenerated into most silent and insignificant arenas of very commonplace business. "It certainly will be. Miss Widgeon," answered Maria, with strictly "company manners." "One who has never had a brother exposed to the constant dangers of army life can hardly understand how glad we all feel to have Si snatched from the very jaws of death and brung back to us." "Just plug at 'em as you would at a crow, and then go on your way whistlin'?" persisted Harry. "Hurroo!" echoed Hennessey; "that's the ticket." "Come forward, keeper," continued the baron, "and state how these arrows came into your hands!" "Yes." HoMEJULIA京香2018下载
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