英语听力:自然百科 神奇水世界 Water-4(在线收听) |
Let's look first. The fresh water that we depend on begins its life in the oceans. As the sun's rays beat down on the surface of the sea, they heat the water molecules until some evaporate. It's the start of an extraordinary journey. Here with water evaporates, it feels like it vanishes into thin air there. Although we barely notice it, water molecules are suspending around us all the time, just that we are only aware of it when they clump together as cloud.
At tiny one time, less than a thousandth of the world's water is up here in the atmosphere. It may not seem much, but this is what spreads water from the seas to the land.
The water molecule doesn't hang around up here for very long. It fact, it spends less time up there in the atmosphere than in any other time of its journey. A mere nine days until a typical water molecule crashes the earth as rain.
For most of us, rain is perhaps the most familiar stage of the water cycle, but notoriously, the least reliable.
As the water falls as rain, it joins a bigger system, cascading and carving its way across the land surface as streams and rivers. Look at that, water, absolutely everywhere.
Rivers and rain are the parts of the water cycle that we depend on and yet they are only a tiny proportion of the world's fresh water, amazingly two percent of all fresh water on the planet, the rest of the earth’s fresh water is locked away, down there on the ground.
What a landing.
The vast majority of it is stored as ice. Most of the rest seeps deep into the earth where it's known as groundwater. Hidden away down here is the planet's second largest store of fresh water, but in the end, all water arrives back in the oceans and the cycle begins again. |
原文地址:http://www.tingroom.com/lesson/zrbaike/2010/259101.html |