公共英语听力材料：海盐的形成

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Salty Seas

Dear A Moment of Science,
I know why the ocean is still salty: evaporated water leaves the salt behind. But how did it get salty in the first place?”—Salty Dog

According to one hypothesis, oceans formed at least 500 million years ago when water vapor and other gasses escaping from the Earth’s interior gradually formed the atmosphere and clouds surrounding the planet. As the earth cooled below the boiling point of water, rain began to fall, and kept falling for centuries. Eventually the rainfall filled the Earth’s hollows and formed oceans.

Salt of the Earth
In their infant state these oceans were not nearly as salty as they are today. As the initial rains swept over the planet’s surface and filtered down to the hollows, the rushing waters picked up chemicals from erosion of the Earth’s crust. These chemicals included sodium, which is one of the main ingredients of salt. The other main ingredient, chlorine, came from the solid and gaseous fallout of land and ocean floor volcanoes. Over hundreds of millions of years the steady flow of chemical-rich rivers and streams and the eruption of volcanoes and undersea vents combined to increase the oceans’ salt content.

This does not mean, however, that the oceans’ saltiness is constantly increasing. Scientists believe that ocean salinity reached a plateau hundreds of millions of years ago, when roughly the same amount of salt fed into the oceans was deposited as sediment on the ocean floor.
咸的海水

亲爱的《科学一刻》

我知道为什么海洋依旧是咸的了：水分蒸发掉，留下了盐。但是一开始盐是怎么进去的呢？——咸味鸡尾酒

有种假设，海洋在至少五亿年前形成。那时水蒸气和其他气体渐渐从地球内部逸出，形成了围绕地球的大气层和云。当地球冷却到水沸点以下，开始下雨，下了好几个世纪。最后，雨水填满了地球的低洼形成了海洋。

地球的盐

在海洋形成初期，它们还不像今天这样咸。最初的雨席卷地球表面后汇入低洼，激流带进去了地壳腐蚀处的化学成分。这些化学成分包括钠，那正是盐的主要成分。另一个主要成分，氯，来自陆上海底火山喷发产生的尘土及气体。经过数亿年，富含化学物质的河流、陆上海底的火山喷发物，合在一起增加了海洋的盐分。

然而，这并不意味着海洋会持续变咸下去。科学家认为，海洋盐度在数亿年前就达

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