英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit08

But even if there had been water, life doesn't start overnight. Even a simple microbe is the product of complex chemical systems that take millions of years to evolve. Had the water lasted long enough for life to form?

Well, when we look at the history of life on Earth, it appears to start very quickly, maybe a hundred million years. Now that seems like a long time, but for a planet that's short. So I would guess that if there was water on Mars for a couple of hundred million years, then life had a good shot at getting started there.

And soon they found evidence that water had been there for millions of years. It was all because of one very important picture. Sent back in December 2000, it was a vast formations of sedimentary rock. Sediment¹ is basically made of sand, and could only have been deposited over millions of years by a huge body of water, like a lake or an ocean. It showed that there had not only been masses of water, but that it had been around easily long enough for life to form. The sediments² on the surface are now dry and exposed. If they ever had contained life, it cannot possibly have survived. However, scientists hope that microbes deeper down might still be alive, frozen in the ground.

To find the actual organic remains³ of a Martian organism, we are gonna need to go to the frozen material. In the ice life might have been preserved, frozen in a state of suspended animation⁴.

No one at this stage could know if microbes, formed millions of years ago, could have survived on Mars. But there are indications that this really is possible.

Antarctica, the closest place on Earth to conditions on Mars. More extreme even than Iceland, it's the coldest place on our planet. Until a few years ago, no one thought that anything could survive being deep frozen for millions of years. But research here has helped change that.

sedimentary rock: Rock formed at or near the Earth's surface by the accumulation and lithification of fragments of preexisting rocks or by precipitation from solution at normal surface temperatures. Sedimentary rocks can be formed only where sediments are deposited long enough to become compacted and cemented into hard beds or strata⁵. They are the most common rocks exposed on the Earth's surface but are only a minor⁶ constituent⁷ of the entire crust. Their defining characteristic is that they are formed in layers. Each layer has features that reflect the conditions during deposition, the nature of the source material (and, often, the organisms present), and the means of transport

1 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

2 sediments   

沉淀物( sediment的名词复数 )； 沉积物

参考例句：

• When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后，体积的70-80％是水。
• Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。

3 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

4 animation   

n.活泼，兴奋，卡通片／动画片的制作

参考例句：

• They are full of animation as they talked about their childhood.当他们谈及童年的往事时都非常兴奋。
• The animation of China made a great progress.中国的卡通片制作取得很大发展。

5 strata   

n.地层（复数）；社会阶层

参考例句：

• The older strata gradually disintegrate.较老的岩层渐渐风化。
• They represent all social strata.他们代表各个社会阶层。

6 minor   

adj.较小(少)的，较次要的；n.辅修学科；vi.辅修

参考例句：

• The young actor was given a minor part in the new play.年轻的男演员在这出新戏里被分派担任一个小角色。
• I gave him a minor share of my wealth.我把小部分财产给了他。

7 constituent   

n.选民；成分，组分；adj.组成的，构成的

参考例句：

• Sugar is the main constituent of candy.食糖是糖果的主要成分。
• Fibre is a natural constituent of a healthy diet.纤维是健康饮食的天然组成部分。