Part I
Pro: So, continuing our discussion of desert lakes, now I want to focus on what's known as the "Empty Quarter". The "Empty Quarter" is a huge area of sand that covers about a quarter of the Arabian Peninsula. Today it's pretty desolate, barren and extremely hot.
But there've been times in the past when monsoon rains soaked the Empty Quarter and turned it from a desert into grassland that was dotted with lakes and home to various animals. There were actually two periods of rain and lake formation: the first one began about 37,000 years ago; and the second one dates from about 10,000 years ago.
Stu: Excuse me, Professor. But I'm confused. Why would lakes form in the desert? It's just sand, after all.
但以前曾有过季风雨水浸透鲁卜哈利沙漠，把它从沙漠变成了遍布着湖泊的草原，变成了各种动物的家。
1. Empty Quarter
The Rub' al Khali (/ˈrʊb æl ˈkɑːli/, the "Empty Quarter") is the sand desert encompassing most of the southern third of the Arabian Peninsula. The desert covers some 650,000 km2 including parts of Saudi Arabia, Oman, the United Arab Emirates, and Yemen. It is part of the larger Arabian Desert. 鲁卜哈利沙漠，意为“空旷的四分之一”，由于其面积占据阿拉伯半岛约四分之一而得名，是世界上最大的流动沙漠，覆盖了整个沙特阿拉伯南部地区和大部分的阿曼、阿联酋和也门领土，面积约65万平方公里，超过荷兰、比利时和法国面积总和。沙漠为1,000公里长，500公里宽，贝都因人既不在此居住，也不穿越这里。夏季近55℃的高温和超过330米高的沙丘使这里成为一个禁区。
2. desolate|ˈdesələt|
adj. empty and without people, making you feel sad or frightened 无人居住的；荒无人烟的；荒凉的
E.g.: Half-ruined, hardly a building untouched, it's a desolate place.
这里大半遭毁，几乎没有一栋建筑完好无损，变成了一块荒废之地。
3. barren |ˈbærən|
adj. not good enough for plants to grow on it 贫瘠的；不毛的
E.g.: He also wants to use the water to irrigate barren desert land.
他也想用这些水灌溉荒漠。
4. dot |dɑ:t|
verb. to spread things or people over an area; to be spread over an area 星罗棋布于；遍布；散布于
E.g.: The countryside was dotted with small villages.
乡间有星罗棋布的小村庄。
Part II
Pro: Good question! We know from modern day desert lakes, like Lake Eyre in South Australia, that under the right conditions, lakes do form in the desert. But the Empty Quarter lakes disappeared thousands of years ago. They left behind their beds or basins as limestone formations that we can still see today. They look like low-lying, white or grey buttes, long, narrow hills with flat tops, barely a meter high.
A recent study of some of the formations presents some new theories about the area's past. Keep in mind though that this study only looked at 19 formations. And about a thousand have been documented. So there's a lot more work to be done.
According to the study, two factors were important for lake formation in the Empty Quarter: first, the rains that fell there were torrential. So it would've been impossible for all the water to soak into the ground. Second, as you know, sand dunes contain other types of particles, besides sand, including clay and silt.
它们只剩下我们今天仍然可以看到的作为河床凹地的石灰岩结构。这些结构看起来像是低洼的白色或灰色小山丘，又长又窄顶部平坦的山丘，只有不到一米高。
1. basin |ˈbeɪsn|
noun. a place where the earth's surface is lower than in other areas of the world 盆地；凹地；海盆
E.g.: The basin favours the development of farming and animal husbandry.
这个盆地有利于农业和畜牧业的发展。
2. limestone 石灰岩, quartz 石英, marble 大理石, obsidian 黑曜石, granite 花岗岩, shale 页岩, basalt 玄武岩
3.low-lying
adj. not high, and usually fairly flat 低的；低洼的
E.g.: The torrential rain may flood the low-lying land out.
这场骤雨有可能把低洼地淹没。
4. butte|bju:t|
noun. a hill that is flat on top and is separate from other high ground 地垛（顶部平坦的小丘、高地）
dune|du:n|
noun. a small hill of sand formed by the wind, near the sea or in a desert （风吹积成的）沙丘
5. document|ˈdɒkjumənt|
verb. to record the details of sth 记录，记载（详情）
E.g.: Causes of the disease have been well documented.
这种疾病的起因已有完备的记载。
6. torrential|təˈrenʃl|
adj. falling in large amounts 倾泻的；如注的
E.g.: There was frequent thunder and lightning, and torrential rain.
雷电交加，大雨倾盆。
7. clay|kleɪ|
noun. a type of heavy, sticky earth that becomes hard when it is baked and is used to make things such as pots and bricks 黏土；陶土
E.g.: As the wheel turned, the potter shaped the clay.
轮子一边转动，制陶工人一边拉坯。
8. silt|sɪlt|
noun. sand, mud, etc. that is carried by flowing water and is left at the mouth of a river or in a harbour （沉积在河口或港口的）泥沙，淤泥，粉沙
E.g.: During the annual floods the river deposits its silt on the fields.
每年河水泛滥时都会在田野上沉积一层淤泥。
Part III
Now, when the rain fell, water ran down the sides of the dunes, carrying clay and silt particles with it, and wherever these particles settled, they formed a pan, a layer that water couldn't penetrate.Once this pan formed, further run-off collected, and formed a lake.
Now, the older lakes, about half the formations, the ones that started forming 37,000 years ago, the limestone formations we see, they're up to a kilometer long, but only a few meters wide, and they're scattered along the desert floor, in valleys between the dunes.
So, the theory is, the lakes formed there on the desert floor, in these long narrow valleys. And we know, because of what we know about similar ancient desert lakes, we know that the lakes didn't last very long, from a few months to a few years on average. As for the more recent lakes, the ones from 10,000 years ago, well, they seemed to have been smaller, and so may have dried up more quickly.
下雨的时候，雨水就会顺着沙丘的两侧流下，带着粘土和淤泥颗粒，这些颗粒沉淀的地方就会形成一个平底，它是不透水的一层。
1. settle |ˈsetl|
verb. to sink slowly down; to make sth do this （使）沉降，下陷，变得密实
E.g.: The contents of the package may have settled in transit.
包裹里的东西可能在运输途中摇密实了。
2. pan |pæn|
noun. a container, usually made of metal, with a handle or handles, used for cooking food in 平锅；平底锅
E.g.: Heat the butter and oil in a large pan.
把黄油和食用油放到大平底锅里加热。
3. penetrate |ˈpenɪtreɪt|
verb. to go into or through sth 穿过；进入
E.g.: These fine particles penetrate deep into the lungs.
这些微小的尘埃可深深地吸入肺部。
4. run-off
noun. rain, water or other liquid that runs off land into streams and rivers 径流，溢流（指流入河流中的雨水）
E.g.: The sewers collected sewage and storm run-off and discharged it, untreated, into the harbour.
污水和暴雨径流汇入下水道后被直接排入海港。
5. up to
as far as a particular number, level, etc. 到达（某数量、程度等）；至多有
E.g.: The temperature went up to 35˚C.
气温上升到了35摄氏度。
6. scatter|ˈskætə(r)|
verb. to move or to make people or animals move very quickly in different directions 散开；四散；使分散；驱散
E.g.: The explosion scattered a flock of birds roosting in the trees.
爆炸声把栖息在树丛中的鸟群惊散了。
Part IV
Another difference, very important today for distinguishing between older lake beds and newer ones, is the location of the limestone formations. The more recent beds are high up in the dunes. Why these differences? Well, there are some ideas about that, and they have to do with the shapes of the sand dunes, when the lakes were formed.
37,000 years ago, the dunes were probably nicely rounded at the top, so the water just ran right down their sides to the desert floor. But there were thousands of years of wind between the two rainy periods, reshaping the dunes. So, during the second rainy period, the dunes were kind of chopped up at the top, full of hollows and ridges, and these hollows would've captured the rain right there on the top.
但在这两次雨期之间刮了数千年的风，重塑了沙丘。
1. have to do with
to relate to or involve someone or something 与…有关; 与…相干;
E.g.: He claims that he had nothing to do with the accident.
他声称他跟那场事故无关。
2. round |raʊnd|
verb. to make sth into a round shape; to form into a round shape （使）成圆形；变圆
E.g.: His eyes rounded with horror.
他吓得两眼圆睁。
3. chop up
to cut (something) into small pieces 切碎；切成小块
E.g.: She chopped up the nuts and added them to the cookie dough.
她把坚果切碎，加到饼干面团里。
4. hollow |ˈhɑ:loʊ|
noun. an area that is lower than the surface around it, especially on the ground 凹陷处；坑洼处
E.g.: She noticed the slight hollows under his cheekbones.
她注意到他颧骨下面的轻微凹陷。
5. ridge |rɪdʒ|
noun. a raised line on the surface of sth; the point where two sloping surfaces join 隆起；脊；垄
E.g.: The ridges on the soles of my boots stopped me from slipping.
我靴子底上有隆起的纹路，使我没有滑倒。
6. capture |ˈkæptʃə(r)|
verb. if you capture something that you are trying to obtain in competition with other people, you succeed in obtaining it 得到;夺得;获得
E.g.: In 1987, McDonald's captured 19 percent of all fast-food sales.
1987年,麦当劳占据了整个快餐业销售额的19%。
Part V
Now, in a grassland of Lake Ecosystem, we'd expect to find fossils from a variety of animals, and numerous fossils have been found at least at these particular sites. But, where did these animals come from? Well, the theory that has been suggested is that they migrated in from nearby habitats where they were already living. Then as the lakes dried up, they died out.
The study makes a couple of interesting points about the fossils, which I hope will be looked at in future studies. At older lake sites, there’s fossil remains from hippopotamuses, water buffalo, animals that spend much of their lives standing in water, and also, fossils of cattle.
However, at the sites of the more recent lakes, there’s only cattle fossils--- additional evidence for geologists that these lakes were probably smaller, shallower, because cattle only use water for drinking. So they survive on much less. Interestingly, there are clams and snail shells; but, no fossils of fish. We're not sure why. Maybe there was a problem with the water. Maybe it was too salty. That's certainly true of other desert lakes.
然而，在最近期的湖泊遗址里只有牛化石——这可以作为地质学家的额外证据，它表明这些湖泊可能更小、更浅，因为对牛来说水只是用来喝的。
1. fossil|ˈfɑ:sl|
noun. the remains of an animal or a plant which have become hard and turned into rock 化石
E.g.: The fossil fuels (coal and oil) are finite resources.
化石燃料（如煤和石油）属于有限资源。
2. numerous |ˈnju:mərəs|
adj. existing in large numbers 众多的；许多的
E.g.: The advantages of this system are too numerous to mention.
这套系统的好处不胜枚举。
3. hippopotamus 河马, buffalo 水牛, cattle 牛, clam 蛤蜊
10个月宝宝每天需要喝多少奶粉？
