《英语流行话题阅读:语境识词4500》88 Is There Life on Mars?

　　Is There Life on Mars?
For most of the 20th century, there has been life on Mars. Or, at least in the minds of the Earthlings, who inhabit its closest planetary neighbor. When at the end of the 19th century, the American astronomer¹ Percival Lowell thought he saw canals on the Red Planet, he was convinced that they were part of a planetwide irrigation system, built by an advanced Martian civilization.
Then, in 1965, the Mariner² 4 spacecraft flew past the Red Planet. It revealed a desolate³ world; the prospects⁴ for life were fading fast. All hope died in 1976, when the Viking Lander of Nasa failed to find a single organic molecule⁵.
Twenty years after the last mission to Mars failed to detect any signs of life, Nasa is preparing another series of missions to the Red Planet to find evidence of life. The new unmanned Nasa missions to Mars are a result of the growing optimism among scientists that life exists, or did exist, on Mars. The strongest evidence in support of life on Mars comes from the study of microbes. Scientists are finding microbes in more and more inhospitable conditions -- in rocks hundreds of meter below the Earth's surface and in volcanic⁶ springs well above the boiling point of water. And these conditions are remarkably⁷ similar to conditions on Mars. These organisms can live and multiply without oxygen or light in extreme temperatures, using only rocks and water to sustain themselves.
Scientists believe that conditions on Mars around 3.8 billion years ago were similar to those of the early Earth, when primitive⁸ organisms were spreading through our oceans. Under these conditions, it is highly probable that life may have arisen on Mars as well.
Even if life did not arisen naturally on Mars, it does not mean that it could not have existed there. Life forms could have been transferred between the Earth and Mars in debris⁹ created by the impact of comets and asteroids¹⁰ on the surface of the two planets. Even today, about 500 tons of material from Mars lands on Earth every year. It is mainly in the form of dust but occasionally a larger chunk¹¹ strikes the Earth. It is in these chunks¹² of rock, which were much larger and more frequent in the past, that life forms could have been transported from planet to planet. But how could these life forms have survived their journey through space full of deadly cosmic radiation? A rock ten meters across would shield life inside it from a lot of radiation and the temperature might only be minus 10 or 20 degrees (Celsius), the sort of thing we have on Earth. A further complication of this theory is that life could have originally arisen on Mars and then be transferred to Earth. In that case, we would be Martians, who colonized¹³ the Earth.
But could life exist on Mars, given that it is a very different world from what it was 3.8 billion years ago? Bathed in ultraviolet radiation from the Sun, it has virtually no atmosphere and no liquid water on the surface. Mars had moved from a warm, wet place to a dead world of dust storms, volcanoes and vast canyons¹⁴. It happened because its carbon dioxide atmosphere could not remain stable in a wet environment. Carbon dioxide reacts with rocks, and it rapidly absorbed by water, where it becomes solid carbonates and sinks to the bottom of seas. It is a greenhouse gas, which traps heat from the Sun. As it disappeared from the Martian atmosphere, the planet began to cool. Its atmosphere grew thinner and all the water on the surface froze. This is a fate that the Earth escaped because of water vapor¹⁵ and other greenhouse gases, constantly present in its atmosphere.
Despite the inhospitable surface of today's Mars, scientists believe that Martian microbes would only fed on rock and water, and they are likely to be kilometers below the surface. There could be water deep underground, kept liquid by inner heat from radioactivity.

1 astronomer   

n.天文学家

参考例句：

• A new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
• He is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。

2 mariner   

n.水手号不载人航天探测器，海员，航海者

参考例句：

• A smooth sea never made a skillful mariner.平静的大海决不能造就熟练的水手。
• A mariner must have his eye upon rocks and sands as well as upon the North Star.海员不仅要盯着北极星，还要注意暗礁和险滩。

3 desolate   

adj.荒凉的，荒芜的；孤独的，凄凉的；v.使荒芜，使孤寂

参考例句：

• The city was burned into a desolate waste.那座城市被烧成一片废墟。
• We all felt absolutely desolate when she left.她走后，我们都觉得万分孤寂。

4 prospects   

n.希望，前途(恒为复数)

参考例句：

• There is a mood of pessimism in the company about future job prospects. 公司中有一种对工作前景悲观的情绪。
• They are less sanguine about the company's long-term prospects. 他们对公司的远景不那么乐观。

5 molecule   

n.分子，克分子

参考例句：

• A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。
• This gives us the structural formula of the molecule.这种方式给出了分子的结构式。

6 volcanic   

adj.火山的；象火山的；由火山引起的

参考例句：

• There have been several volcanic eruptions this year.今年火山爆发了好几次。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

7 remarkably   

ad.不同寻常地，相当地

参考例句：

• I thought she was remarkably restrained in the circumstances. 我认为她在那种情况下非常克制。
• He made a remarkably swift recovery. 他康复得相当快。

8 primitive   

adj.原始的；简单的；n.原(始)人，原始事物

参考例句：

• It is a primitive instinct to flee a place of danger.逃离危险的地方是一种原始本能。
• His book describes the march of the civilization of a primitive society.他的著作描述了一个原始社会的开化过程。

9 debris   

n.瓦砾堆，废墟，碎片

参考例句：

• After the bombing there was a lot of debris everywhere.轰炸之后到处瓦砾成堆。
• Bacteria sticks to food debris in the teeth,causing decay.细菌附着在牙缝中的食物残渣上，导致蛀牙。

10 asteroids   

n.小行星( asteroid的名词复数 )；海盘车，海星

参考例句：

• Asteroids,also known as "minor planets",are numerous in the outer space. 小行星，亦称为“小型行星”，在外太空中不计其数。
• Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。

11 chunk   

n.厚片，大块，相当大的部分（数量）

参考例句：

• They had to be careful of floating chunks of ice.他们必须当心大块浮冰。
• The company owns a chunk of farmland near Gatwick Airport.该公司拥有盖特威克机场周边的大片农田。

12 chunks   

厚厚的一块( chunk的名词复数 )； （某物）相当大的数量或部分

参考例句：

• a tin of pineapple chunks 一罐菠萝块
• Those chunks of meat are rather large—could you chop them up a bIt'smaller? 这些肉块相当大，还能再切小一点吗？

13 colonized   

开拓殖民地，移民于殖民地( colonize的过去式和过去分词 )

参考例句：

• The area was colonized by the Vikings. 这一地区曾沦为维京人的殖民地。
• The British and French colonized the Americas. 英国人和法国人共同在美洲建立殖民地。

14 canyons   

n.峡谷( canyon的名词复数 )

参考例句：

• This mountain range has many high peaks and deep canyons. 这条山脉有许多高峰和深谷。 来自辞典例句
• Do you use canyons or do we preserve them all? 是使用峡谷呢还是全封闭保存？ 来自互联网

15 vapor   

n.蒸汽，雾气

参考例句：

• The cold wind condenses vapor into rain.冷风使水蒸气凝结成雨。
• This new machine sometimes transpires a lot of hot vapor.这部机器有时排出大量的热气。