英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit03（在线收听）

Conditions on Mars were so harsh that it was hard to imagine any life surviving there. The idea of sophisticated aliens was wiped out.

We know that conditions on Mars today are not very good for life. If you were to go out on the Mars without a spacesuit, I don't recommend it. But if you were, what would happen is your body fluids would literally start to boil, because vapor pressure on Mars is lower than the boiling point of water at body temperature. So this would not be a very good thing in terms of your ears, eyes, nose and throat. You would quickly suffocate and essentially drown in your own bodily fluid."

It was clear that Mars could not be home to advanced life forms. For a while it meant that perhaps we were alone after all. Mars, it seemed, was a dead end. It wasn't until years later during expeditions in the 70s that they saw that the image of Mars as a dead planet was not quite right.

After a while when people start thinking about it though, you look more into it, then you start realizing “Well, yeah, it is desolate. It's very dry.” But you know there are other things going on.

Volcanoes and explosions had clearly once torn across this planet, leaving the surface pockmarked and scarred. Far from being dead, Mars had all the features of once being very much alive.

We started seeing all these incredible things.

It has mountains there bigger than any mountains on Earth. It's got canyons that are bigger than the Grand Canyon.

All these volcanoes, parts of Mars was cratered, parts weren't.

It's got tremendous altitude variations over the surface of the planet. It's just a very rich environment.

So that was a very exciting, exciting time. I was surprised by almost everything.

It wasn't just the geology of Mars that was surprising. It also contained all the basic ingredients for life.

Here was a planet that had all the elements needed for life, carbon, oxygen, nitrogen, sunlight. And yet there was no clear evidence of life. To me this was a mystery story; it was a sort of lights-are-on-but-nobody's-home result.

So life could form on Mars. There's nothing there preventing it. We do have the basic building blocks.

body fluid: a natural bodily fluid or secretion of fluid such as blood, semen, or saliva; total body water, contained principally in blood plasma and in intracellular and interstitial fluids

vapor pressure: the pressure exerted by a vapor in equilibrium with its solid or liquid phase

pockmarked: marked by smallpox; pitted