Earth and Sky:Water Cycle 水循环

 

Water Cycle 水循环

All the oceans on earth are salty, while inland water is typically fresh. How does water become salty? We'll answer a listener's question -- today on Earth and Sky.

DB: This is Earth and Sky. We recently visited the Austin Children's Museum in Texas to record your science questions. This one is from Jeana Lungwitz.

Jeana Lungwitz: Why are the oceans salt water and the rivers and lakes typically fresh water?

JB: Jeana, first imagine a tea kettle. If you boil tap water to make tea, some of it evaporates. After a while, you might notice a hard crust of mineral deposits forms on the bottom of your teapot

DB: That crust is there because when tap water evaporates it leaves behind any dissolved salts and minerals. Now take this scenario¹ to the ocean. Most water on Earth evaporates from the surface of the ocean. There it leaves behind dissolved salts. Then, when water precipitates² out of the atmosphere, it falls as fresh water.

JB: The freshwater that falls onto land cascades³ over surfaces like rocks and sediments⁴. Here it picks up nutrients⁵, chemicals, and salts. The water carries the dissolved salts on its long journey back to sea. If you run this water cycle over and over again, through four and a half billion years, you eventually leave a lot of salt in the ocean.

DB: In fact, if you came back in another billion years, the ocean would be even saltier than it is now. Thanks for your question Jeana. And with thanks to the National Science Foundation, we're Block and Byrd for Earth and Sky.

1 scenario   

n.剧本，脚本；概要

参考例句：

• But the birth scenario is not completely accurate.然而分娩脚本并非完全准确的。
• This is a totally different scenario.这是完全不同的剧本。

2 precipitates   

v.（突如其来地）使发生( precipitate的第三人称单数 )；促成；猛然摔下；使沉淀

参考例句：

• Water precipitates camphor from its alcoholic solution. 水能把樟脑从其酒精溶液中淀析出来。 来自《简明英汉词典》
• Precipitates are usually collected by centrifugation at intervals. 常常是用离心法分段收集沉淀的。 来自辞典例句

3 cascades   

倾泻( cascade的名词复数 )； 小瀑布（尤指一连串瀑布中的一支）； 瀑布状物； 倾泻（或涌出）的东西

参考例句：

• The river fell in a series of cascades down towards the lake. 河形成阶梯状瀑布泻入湖中。
• Turning into the sun, he began the long, winding drive through the Cascades. 现在他朝着太阳驶去，开始了穿越喀斯喀特山脉的漫长而曲折的路程。 来自英汉文学 - 廊桥遗梦

4 sediments   

沉淀物( sediment的名词复数 )； 沉积物

参考例句：

• When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后，体积的70-80％是水。
• Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。

5 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》