[科学美国人60秒] SSS 2015-11-20

搜索关注在线英语听力室公众号：tingroom，领取免费英语资料大礼包。

  Back in  real life scientists have found something else covered by this Sahara sea of sand, an ancient river system. The remains² of the main channel, which dried up long ago, wind beneath the West African desert  for more than three hundred miles before reaching the Atlantic Ocean. Researchers led by Shylock of the University of Leon in France uncovered the system using a kind of satellite-borne radar³ that can penetrate⁴ through several feet of dry surface elements like sand. The scientists think the network may extend even  farther inland. But thick domes⁵ prevent them from mapping it. They reported their findings in the journal Nature Communications. The discovery  appeared to solve the mystery of what created a vast underwater canyon⁶ off the coast of ? in northeast Africa. The subsurface looks like those that form the mouth of the massive rivers today. But researchers had only hypothesizedt he existence of major waterways in west Africa until now. The fact that rivers once raged in this region shed light on the Sahara's tumultuous history. Scientists know that this vast desert wasn't always dry. At certain times in the past, it boasted green grasslands⁷ teeming⁸ with life. The researchers think the Sahara's lost river last flowed sixty-five hundred years ago, revealing just how fast west Africa's climate can change.  Maybe not quite as fast as Indiana Jones swapping⁹ up a bag of sand for a golden idol¹⁰, but still, surprisingly fast.

  Wipe clean

分享到：