[ti:Scientist Might Have Found Earliest Evidence of Animal Life on Earth]
[by:www.21voa.com]
[00:00.00]更多听力请访问21VOA.COM
[00:01.36]A Canadian scientist might have found
[00:04.80]the earliest evidence of animal life on Earth.
[00:10.16]Geologist Elizabeth Turner presented her findings
[00:14.36]in the science publication Nature in late July.
[00:20.36]Turner made her discovery in the rocks
[00:23.64]of Canada's Northwest Territories.
[00:28.24]She has been doing research there since the 1980s.
[00:34.28]The area where she works has high mountains
[00:38.04]and can only be reached by helicopter.
[00:42.56]But an estimated 890 million years ago,
[00:48.20]the area was under the sea.
[00:52.28]There, Turner said she found the remains
[00:56.20]of sponges preserved as minerals in rock.
[01:01.36]The rock contains structures that look like
[01:05.16]modern sponges that live in the world's oceans.
[01:10.68]Joachim Reitner is an expert on sponges
[01:15.12]at Germany's University of Gottingen.
[01:20.64]Reitner was not involved in the research.
[01:24.56]But he agreed the findings must be a kind of sponge.
[01:31.36]Dating of rock levels
[01:34.24]suggests that the rocks containing the structures
[01:38.60]are about 890 million years old.
[01:44.48]That would make them about 350 million years older
[01:50.48]than the oldest sponge fossils found during earlier studies.
[01:56.84]Paco Cardenas is an expert on sponges
[02:01.24]at Sweden's Uppsala University
[02:04.84]and was not involved in the research.
[02:09.88]He said the date of the sponge is the most shocking thing about it.
[02:16.20]Discovering sponge fossils from close to 900 million years ago
[02:22.76]will improve our understanding of early animal life, he said.
[02:29.64]Many scientists believe the first animal groups included sponges
[02:35.92]or sponge-like creatures without muscles or nerves.
[02:40.68]But they had other qualities of simple animals, including cells
[02:47.04]for different purposes and sperm for reproduction.
[02:53.60]However, there is very little scientific agreement
[02:58.20]about things that happened one billion years ago.
[03:02.56]So other researchers will continue
[03:05.84]to examine and debate Turner's findings.
[03:10.76]"I think she's got a pretty strong case.
[03:13.64]I think this is very worthy of publishing.
[03:17.76]It puts the evidence out there for other people to consider," said David Bottjer.
[03:26.04]He is a paleobiologist at University of Southern California
[03:32.08]and was not involved in the research.
[03:36.44]Scientists believe life on Earth appeared 3.7 billion years ago.
[03:44.48]The earliest animals appeared much later but exactly when is still debated.
[03:52.72]The oldest undisputed fossil sponges date
[03:57.00]to around 540 million years ago, a time called the Cambrian period.
[04:05.96]Some scientists using a method called the molecular clock
[04:11.00]say evidence suggests sponges appeared around a billion years ago.
[04:18.48]The molecular clock method dates changes in living things
[04:24.36]based on the idea that genetic change
[04:28.04]takes place at a regular rate over long periods of time.
[04:35.24]But no supporting physical evidence
[04:37.92]for the first appearance of sponges had been found.
[04:43.40]"This would be the first time that a sponge fossil has been found
[04:48.56]from before the Cambrian, and not only before, but way before
[04:54.20]— that's what's most exciting," said Cardenas.
[04:59.76]He added that the research seems to confirm
[05:03.52]the molecular clock estimates.
[05:07.80]Little fossil evidence exists before the Cambrian period,
[05:13.12]when animals first developed hard bones, exoskeletons and shells.
[05:20.96]Those structures are more likely to be preserved.
[05:26.24]The time period of 890 million years ago is important.
[05:33.80]If the organism is confirmed as a sponge,
[05:37.40]the discovery would prove that the first animals developed
[05:42.32]before oxygen reached a level scientists thought
[05:47.40]was needed for animal life.
[05:50.96]But recent research suggests
[05:53.60]that some sponges can survive with little oxygen.
[05:59.80]"Everything on Earth has an ancestor," said Roger Summons.
[06:05.36]He is an MIT geobiologist
[06:10.36]who also was not involved in the research.
[06:14.92]He said it has always been predicted
[06:18.12]that the first proof of animal life
[06:21.24]would be small and mysterious.
[06:25.32]I'm Alice Bryant. 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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