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VOA慢速英语2013 AS IT IS - Earth Day 地球日

时间:2013-04-23 01:45:54

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AS IT IS - Earth Day

地球日

This is AS IT IS.

Hi, I’m Caty Weaver1.  Today is Earth Day. Millions of people around the world will pick up trash, learn about recycling, plant trees or take some other action to observe the day.

On AS IT IS we take a look at two recent environmental studies that improve our understanding of the natural world.

A new study disputes a widely held belief about how evolutionary2 changes in organisms take place. Scientists have long believed that such changes take place slowly --- over hundreds, thousands or millions of years.

But now, new evidence suggests species can evolve much more quickly when they have to. Avi Arditti has the story.

Tim Benton is a professor of biology at the University of Leeds, in Britain. He studies how living organisms react to changes in their environment. He and other researchers just published a paper on the subject in the journal Ecology. The paper examines why ocean species have dropped so sharply in size and number over the past 50 years.

“Is this a response that is due to them having less food or the temperature of the water changing from climate change or is it a response that is due to natural selection working and evolutionary biology happening?”

To find the answer, Professor Benton’s team of researchers carried out a series of laboratory experiments with soil mites4. Soil mites are very small spider-like creatures that reproduce quickly. The researchers captured mites in the wild and put them in test tubes. Each tube had about one thousand mites.

“Every day, we just put in a little bit of food. And in some of the populations we took out the juveniles5 and in other populations we harvested the adults. And then we just left them to it over about 100 weeks.”

That is normally enough time for about 20 generations of soil mites. However, in the controlled environment, the soil mites competed for food, sex and survival in different ways than they would have in the wild.

The researchers measured the insects’ growth rates, genetics and reproduction over this relatively6 brief period. They observed that natural selection produced meaningful evolutionary changes. As Tim Benton observed, the length of time it took the mites to reach adulthood7 doubled during the experiment.

“And because it is taking them so much longer to grow up, then that means that the population responds to changes in a different way. Population growth rate is slower, which means that there are very large changes in population dynamics8, the way the population size responds to environmental change in itself.”

Professor Benton says the mite3 study suggests there is a powerful relationship between environmental and evolutionary change. He says more studies like this need to be done by different groups. If those result in similar findings, he says, people will more easily accept the force of evolutionary change in ecological9 time.

“So over a single life time, one hundred years, there are likely to be very large changes and if we don’t start thinking about the evolutionary changes as well as the changes in the environment, then the things we put in place to protect the species we want to manage won’t actually work.”

The researcher says fisheries management is one place where the findings might have a critical effect.

“Given that we’re harvesting large animals all the time --- that’s what we do when we go out fishing --- the phenotypic response that we see in the reduction of size is likely to be an evolutionary response. And that’s what we found in out laboratory study. So what that means is if you stop fishing because your stock is getting depleted10 and the animals are increasingly smaller, there is no necessity that they will be able to recover because you’ve had a hard-wired evolutionary change. So they won’t just be able to spring back.”

And there is no guarantee they will again grow larger and larger.

Professor Benton adds that environmentally-led evolutionary changes could have serious effects on other wildlife protection efforts, and on disease and insect control programs.

As the team at Leeds studies interactions between evolution and the environment, another group of scientists is following pollutants11 by examining trees. Jim Tedder12 reports on the investigation13.

Much clothing, furniture and other products are covered with chemicals meant to slow the spread of fire. These fire retardants, however, can become poisons in nature. And they are in the environment. The chemicals are found in water, plants and the air. In the past, scientists had difficulty measuring the levels of these pollutants. But that recently changed with a technique developed by researchers at Indiana University.

Researcher Amina Salamova studies polybrominated diphenyl ethers and other chemical pollutants. PBDEs are widely used as fire retardants. But they have also been linked to human health problems.

Ms. Salamova explains.

“They can have an effect on neurological development, on reproductive system and they can affect your thyroid endocrine system.”

Concerns about those effects have led some government agencies and manufacturers to end the use of many chemical products. But, PBDEs can exist for years in the environment. Scientists do not know exactly where or how they spread.

That is why Amina Salamova and researcher Ronald Hites developed a new way to measure the presence and amount of PBDEs in the air. They do so be testing the bark covering trees.

“The tree’s ideal because it’s sitting there passively soaking up these compounds out of the atmosphere.”

A tree’s bark provides a large surface area that takes in the chemicals as both gasses and particles. A layer of bark remains14 on a tree for about five years. So it provides a record of the environment over time.

The current more common method of tracking PBDEs is complex. It involves forcing air through costly15 equipment. This also requires a lot of electricity and workers.

Amina Salamova says the tree bark method is a clear improvement.

“So what I see in future for tree bark is the ability to use this method in developing countries which don’t have a lot of funding for elaborate atmospheric16 studies. Also we can use this method in remote sites where there is no power.”

The two scientists have received bark from twelve areas, including Norway, the Czech Republic, South Africa and Indonesia.

In the laboratory researchers found evidence of fire retardants in the atmosphere at all twelve areas. The highest levels were found in the United States and Canada. What was surprising, however, was the high level found in some rural parts of Indonesia and Tasmania.

“There’s hardly anybody there. It’s really out of the winds of possible industrial pollutants.”

The researchers’ findings show the compounds are travelling surprisingly long distances. Amina Salamova says they hope to continue collecting tree bark to build a worldwide information base. That way scientists and governments can understand the extensiveness of fire retardants and find ways to remove them from the environment.

And that’s AS IT IS for today. I’m Caty Weaver.


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点击收听单词发音收听单词发音  

1 weaver LgWwd     
n.织布工;编织者
参考例句:
  • She was a fast weaver and the cloth was very good.她织布织得很快,而且布的质量很好。
  • The eager weaver did not notice my confusion.热心的纺织工人没有注意到我的狼狈相。
2 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
3 mite 4Epxw     
n.极小的东西;小铜币
参考例句:
  • The poor mite was so ill.可怜的孩子病得这么重。
  • He is a mite taller than I.他比我高一点点。
4 mites d5df57c25d6a534a9cab886a451cde43     
n.(尤指令人怜悯的)小孩( mite的名词复数 );一点点;一文钱;螨
参考例句:
  • The only discovered animals are water bears, mites, microscopic rotifers. 能够发现的动物只有海蜘蛛、螨和微小的轮虫。 来自辞典例句
  • Mites are frequently found on eggs. 螨会经常出现在蛋上。 来自辞典例句
5 juveniles 257c9101f917ec8748aa5fc520c6a9e3     
n.青少年( juvenile的名词复数 );扮演少年角色的演员;未成年人
参考例句:
  • Do you think that punishment for violent crimes should be the same for juveniles and adults? 你对暴力犯罪的惩罚对于青少年和成人应一样吗? 来自生活英语口语25天快训
  • Juveniles Should we not exactly in need of such strength and conviction? 少年的我们难道不正是需要这种力量和信念吗? 来自互联网
6 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
7 adulthood vKsyr     
n.成年,成人期
参考例句:
  • Some infantile actions survive into adulthood.某些婴儿期的行为一直保持到成年期。
  • Few people nowadays are able to maintain friendships into adulthood.如今很少有人能将友谊维持到成年。
8 dynamics NuSzQq     
n.力学,动力学,动力,原动力;动态
参考例句:
  • In order to succeed,you must master complicated knowledge of dynamics.要取得胜利,你必须掌握很复杂的动力学知识。
  • Dynamics is a discipline that cannot be mastered without extensive practice.动力学是一门不做大量习题就不能掌握的学科。
9 ecological IrRxX     
adj.生态的,生态学的
参考例句:
  • The region has been declared an ecological disaster zone.这个地区已经宣布为生态灾难区。
  • Each animal has its ecological niche.每种动物都有自己的生态位.
10 depleted 31d93165da679292f22e5e2e5aa49a03     
adj. 枯竭的, 废弃的 动词deplete的过去式和过去分词
参考例句:
  • Food supplies were severely depleted. 食物供应已严重不足。
  • Both teams were severely depleted by injuries. 两个队都因队员受伤而实力大减。
11 pollutants 694861490fe64672170a0da250a277c7     
污染物质(尤指工业废物)( pollutant的名词复数 )
参考例句:
  • Pollutants are constantly being released into the atmosphere. 污染物质正在不断地被排放到大气中去。
  • The 1987 Amendments limit 301(g) discharges to a few well-studied nonconventional pollutants. 1987年的修正案把第301条(g)的普通排放限制施加在一些认真研究过的几种非常规污染物上。 来自英汉非文学 - 环境法 - 环境法
12 tedder 2833afc4f8252d8dc9f8cd73b24db55d     
n.(干草)翻晒者,翻晒机
参考例句:
  • Jim Tedder has more. 吉姆?特德将给我们做更多的介绍。 来自互联网
  • Jim Tedder tells us more. 吉姆?泰德给我们带来更详细的报道。 来自互联网
13 investigation MRKzq     
n.调查,调查研究
参考例句:
  • In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
  • He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。
14 remains 1kMzTy     
n.剩余物,残留物;遗体,遗迹
参考例句:
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
15 costly 7zXxh     
adj.昂贵的,价值高的,豪华的
参考例句:
  • It must be very costly to keep up a house like this.维修这么一幢房子一定很昂贵。
  • This dictionary is very useful,only it is a bit costly.这本词典很有用,左不过贵了些。
16 atmospheric 6eayR     
adj.大气的,空气的;大气层的;大气所引起的
参考例句:
  • Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
  • Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。

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