听力(5)Lecture geology class.
1)The "EmptyQuarter" is a huge area of sand that covers about a quarter of the ArabianPeninsula.
2)But there've beentimes in the past when monsoon rains soaked the Empty Quarter and turned itfrom a desert into grassland that was dotted with lakes and home to variousanimals.
3)Keep in mind thoughthat this study only looked at 19 formations. And about a thousand have beendocumented.
4)So, the theory is, the lakes formed there, along the desert floor, in these longnarrow valleys.
5)Another difference,very important today for distinguishing between older lake beds and newer ones,is the location of the limestoneformations. The more recent beds are high up in the dunes.
6)So, during the second rainy period, the dunes werekind of chopped up at the top,full of hollows andridges, and these hollows would'vecaptured the rain right there on the top.
7) 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 is a problem with the water. Maybe it was too salty. That's certainly true of otherdesert lakes.