英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit07（在线收听）

Rice had seen the same thing in Iceland, one of the few places on Earth with similarities to Mars. It too is extremely cold, and most of the water is frozen into glaciers. And also like Mars, buried underground, are massive volcanoes. This powerful combination has shaped the entire landscape. When a volcano erupts, lakes of steaming melt water form high up on top of the glacier until the enormous weight of water forces its way down, bursting out from the base of the glacier. These are the biggest floods on Earth, a surging wall of water stretching for kilometers. In their wake they leave vast planes littered with boulders. To a geologist these boulder fields contain unmistakable evidence of the floodwaters that ripped through here.

Okay, well this is really a classic textbook example, these two large boulders here. The size of them indicates this was an enormous flood that deposited these features, but also if you look at their geometry, these boulders are kind of dipping back in this direction. This has given us information about the path that floodwaters took that deposited these boulders. The floodwaters were going in this direction when these rocks were deposited. Now there is other interesting things in the scene here. For instance, notice some of these smaller rocks are very well rounded, and these little nicked corners of these boulders here, these are kind of percussion marks and these are produced in a water, highly turbulent water column when the boulders and rocks are basically slamming into one another, knocking the corners off. These things all grouped together just tell you there’s no doubt this was a catastrophic flood deposit.

The pictures from Mars showed the rocks in exactly the same pattern as on Iceland. Here were the slanting boulders lined up by the floodwaters. And the cameras on the rover provided detailed views of the individual rocks, with their telltale chipped edges. It seemed that the vast Martian channels had been carved by enormous floods. It was final confirmation that Mars had once been warm and wet like the Earth, and that meant that there really was every chance for life to have evolved there.

deposit:(动词)to lay down or leave behind by a natural process

(名词)Something deposited, especially by a natural process, as:

a: Geology. A concentration of mineral matter or sediment in a layer, vein, or pocket

b: Physiology. An accumulation of organic or inorganic material, such as a lipid or mineral, in a body tissue, structure, or fluid.

c: A sediment or precipitate that has settled out of a solution.