英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit14（在线收听）

Well, hearing that Odyssey had found subsurface water on Mars was enormously exciting for somebody who is involved in planning to send humans to Mars. Water has a number of important uses for us. At the most basic, it provides drinking water once it's been purified, and it provides water for hygiene purposes as well. More important than that, we can electrolyze it, we can actually split it into hydrogen and oxygen, oxygen obviously we can use for breathing and we can also use it as a fuel stock with the hydrogen for our vehicle to come back home. And we can also use the hydrogen itself in fuel cells to power our rover vehicles. So the ability to use water that exists on Mars is tremendously important to human missions on Mars.

But any colonizing of Mars would require extreme action. Some believe it would need what scientists call'terraforming', transforming the entire planet into an artificial Earth. This involves growing plants to create more oxygen, and an atmosphere.

It requires raising the temperature of the planet, raising the atmospheric density through melting the icecaps and freeing up the carbon dioxide. But the key thing about the water ice on Mars is once we've done that, then we can let that water exist free form on surface of the planet, it again will create rivers, lakes, oceans which we can use and the plants can use to survive.

But plants grown on Mars may be very different from those on Earth. The lower gravity on Mars, one third of that on Earth means that both plants and animals might grow taller and thinner.

I think we're all familiar with seeing the giant redwood trees of California. They are somewhat unusual here on Earth. They only occur in a few localized places. On Mars, it would be the norm. You would see these tremendously tall, slim trees, possibly with very high canopies on them as well. Animal life could be affected the same way as well. We could see new breeds of animal that we haven't seen before, very tall, thin sheep living on Mars. But again early days, very much speculative.

This lower gravity would also have implications for any people born there.

If humans live on Mars for many generations, they might develop into different forms than humans on Earth. They might be taller, they might be thinner, they might have weaker muscles and weaker bones. It might even be possible that they would not be able to function very effectively on the gravity of Earth. In that case, Mars' society and Earth's society might split and become effectively two different species.

subsurface water(also underground water): water that is found in cavities beneath the surface of the land

electrolyze(also electrolyse): separate a substance using electric currents, chemically separate a substance

terraforming: is the theoretical process of modifying a planet, moon, or other body to a more habitable atmosphere, temperature, or ecology. It is a type of planetary engineering. The term is sometimes used broadly as a synonym for planetary engineering in general. The concepts of terraforming are rooted both in science fiction and actual science

localized(also localised): confined to a particular place; concentrated in particular location

canopy: The uppermost layer in a forest, formed by the crowns of the trees. Also called crown canopy