Much of the Sahara is underlain by an enormous freshwater aquifer.

撒哈拉绝大部分区域是由底下的 巨大淡水地下蓄水层支撑。

And I think it's particularly true in the Arctic because it's underlain by all this frozen ground.

“我认为海狸对北极地区的影响尤为重要，因为北极地下全是这种冻土。”

We now know that these plains that you see stretching behind me are underlain only two or three inches deep by a sheet of ice.

我们现在了解到你在我身后看到的这些平原是只有两三英寸深的一片冰。