大气低层的水汽量在干燥地区（量）甚微，而在潮湿地区按体积占4%左右。

Water vapor in the lower atmosphere can vary in amount from a mere trace in arid regions to about 4% by volume in moist areas.

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修建这些水坝可提供廉价的电力，为工人创造就业机会，刺激了地区经济发展，并允许在否则将过于干燥的土地上进行耕种。

Building these dams provided cheap electricity, created jobs for workers, stimulated regional economic development, and allowed farming on lands that would otherwise be too dry.

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科学家们已经确定，在埃塞俄比亚阿法尔地区干燥河床的细颗粒沉积物中发现的具有锋利边缘的石片存在于252万至260万年前。

Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago.

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