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Lecturer:So,continuing our discussion of desert lakes, now I want to focus on what's known as the Empty Quarter.
演講者:那么，我們繼續討論沙漠湖泊，現在我想主要說說空白地區。
The Empty Quarter is a huge area of sand that covers about a quarter of the Arabian Peninsula.
空白地區是一大塊覆蓋了四分之一的阿拉伯半島的沙漠地帶。
Today it's pretty desolate, barren and extremely hot.
現今那里非常荒涼，土地貧瘠而且極其炎熱。
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.
但在過去一段時間里，季風雨將滋潤這一地區并將它從沙漠轉變成綠地，其上湖泊星羅棋布，各種動物在此安家。
There were actually two periods of rain and lake formation:
事實上，這里有過兩次降雨和湖泊形成期:
the first one began about 35000 years ago; and the second one dates from about 10000 years ago.
第一次發生在 35000年前，第二次可追溯到 10000 年前。
Female Student:Excuse me, Professor.
女學生:不好意思，打斷一下，教授。
But I'm confused. Why would lakes form in the desert?
我有點不解，為什么沙漠里會有湖泊形成呢？
It's just sand, after all.
沙漠里都是沙子啊。
Lecturer:Good question! We know from modern day desert lakes, like Lake Eyre, South Australia, that under the right conditions, lakes do form in the desert.
演講者:問得好！我們現在知道，像澳大利亞南部的艾爾湖，就是在正常的沙漠條件下形成了的湖泊。
But the Empty Quarter lakes disappeared thousands of years ago.
但是幾千年前空白地帶的湖泊就消失了。
They left behind their beds or basins as limestone formations that we can still see today.
這些湖泊沉積礦或某些流域是作為石灰巖層存留至今,我們仍然可以看到。
They look like low-lying, white or grey builds, long, narrow hills with flat tops, barely a meter high.
地處低洼地帶，灰白相間，看起來像狹長而平頂的山丘，幾乎不到一米高。
A recent study of some of the formations presents some new theories about the area's past.
最近對于某些巖層的研究中提到了關于該地區過去形態的某些理論。
Keep in mind though that this study only looked at 19 formations.
記住，這次研究只是針對19種構造進行的。
And about a thousand have been documented.
而將近1000種構造已經被記錄在冊。
So there's a lot more work to be done.
所以我們還有很多研究要做。
According to the study, two factors were important for lake formation in the Empty Quarter:
根據此次研究，空白地帶的湖泊構造有兩個重要的因素:
first the rains that fell there were torrential.
第一，該地區的降雨是傾盆而注的，
So it would've been impossible for all the water to soak into the ground.
而本來所有的雨水是不可能滲入到地底下的。
Second, as you know, sand dunes contain other types of particles, besides sand, including clay and silt.
第二，你們知道，沙丘中含有其他種類的粒子，除了沙子之外，還包括黏土和泥沙。
Now, when the rain fell, water ran down the sides of the dunes, carrying clay and silt particles with it.
如今，降雨的時候，雨水會沿著沙丘兩邊留下，帶走黏土和泥沙顆粒。
And wherever these particles settled, they formed a pan, a layer that water couldn't penetrate.
不管什么時候這些顆粒停留下來了，他們便會形成一塊面板，這是一層水分無法滲透的面板。
Once this pan formed, further run-off collected, and formed a lake.
面板一旦形成，顆粒便會有更多流失，從而形成湖泊。
Now, the older lakes, about half the formations, the ones started forming 35000 years ago, the limestone formation we see, they're up to a kilometer long, but only a few meters wide,
而年代更為久遠的湖泊，大概占到一半的構造，它們于 35000 年前就已經形成。我們所看到的石灰巖層高達一千米，而寬卻只有幾米。
and they're scattered along the desert floor, in valleys between the dunes.
他們沿著沙漠地板和沙丘間山谷分布。
So, the theory is, the lakes formed there, along the desert floor, in these long narrow valleys.
所以，這里的理論是，湖泊沿著沙漠地板在這些狹長的山谷中形成。
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.
而我們知道，正因為我們了解相類似的古代沙漠湖泊，我們才知道這些湖泊存在的時間不長，平均是幾個月到幾年時間。
As for the more recent lakes, the ones from 10000 years ago, well, they seemed to have been smaller, and so may have dried up more quickly.
而對于比較近期才形成的湖泊，那些 10000 年前形成的湖泊，嗯，他們似乎更為小，所以可能會更快干涸。
Another difference, very important today for distinguishing between older lake beds and newer ones, is the location of the limestone formations.
另一個今天我們要談到的區別，區分年代久遠和近期形成的湖泊沉積礦，就是石灰巖層的所在地。
The more recent beds are high up in the dunes.
近期的沉積礦在沙丘中位置更高。
Why these differences?
為什么有這些不同呢？
Well, there are some ideas about that, and they have to do with the shapes of the sand dunes, when the lakes were formed.
嗯，這里有一些說法，這些沉積礦跟沙丘的形狀有關。
37000 years ago, the dunes were probably nicely rounded at the top, so the water just ran right down their sides to the desert floor.
37000 年前湖泊形成的時候，沙丘的頂部很可能是圓狀的，因此雨水就只是從兩邊順勢流到沙漠地表。
But there were thousands of years of wind between the two rainy periods, reshaping the dunes.
而在兩個雨季之間幾千年來刮風不止就重新塑形沙丘。
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.
那么在第二次雨季期間，沙丘的頂部被分割成滿是凹陷的空洞和隆起線，而這些洞就足以儲存從頂部留下的雨水。
Now, in 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.
如今，在湖泊生態系統的草地上，我們期望發現各種動物的化石，而至少在某些特定的地方我們已經發現了很多化石。
But, where did these animals come from?
但是，這些動物是從哪里來的呢？
Well, the theory that has been suggested is that they migrated in from nearby habitats where they were already living.
嗯，該理論一直以來說的就是動物從附近的棲息地遷徙而來。
Then as the lakes dried up, they died out.
隨著湖泊干涸，動物滅絕。
The study makes a couple of interesting points about the fossils, which I hope will be looked at in future studies.
此次研究中有幾個有趣的點是關于化石的，我希望這些點在未來的研究中會被重視。
At older lake sites, their fossil remains from hippopotamuses, water buffalo, animals that spend much of their lives standing in water, and also, fossils of cattle.
在年代久遠的湖泊遺址中，發現的化石是河馬，水牛這些在水中長時間生活的生物，還有，牛的化石。
However, at the sites of the more recent lakes, there're only cattle fossils, additional evidence for geologists that these lakes were probably smaller, shallower, because cattle only use water for drinking.
然而，在較為近期形成的湖泊遺址中，卻只發現了牛的化石，對于地理學家來說，這是另外的證據，證明湖泊很可能更小更淺，因為牛只飲水。
So they survive on much less.
所以他們存活的數量要少很多。
Interestingly, there are clams and snail shells; but, no fossils of fish.
有趣的是，還有蛤蜊和蝸牛殼，但是沒有魚的化石。
We're not sure why.
我們不確定為什么。
Maybe there is a problem with the water.
也許是湖水的問題。
Maybe it was too salty.
也許湖水太咸了。
That's certainly true of other desert lakes.
其他的沙漠湖泊湖水確實如此。
