《新版新概念英语第三册(英音)Lesson (55)》歌词

歌曲： 新版新概念英语第三册(英音)Lesson (55)

所属专辑：新版新概念英语第三册(英音)

歌手： 朗文

时长： 03:58

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--- lesson 55 from the earth: greetings[00:00:01]

--- listen to the tape then answer the question below.[00:00:07]

--- which life forms are most likely to develop on a distant planet?[00:00:13]

recent developments in astronomy have made it possible to detect planets in our own milky way and in other galaxies.[00:00:20]

this is a major achievement because, in relative terms, planets are very small and do not emit light.[00:00:28]

finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.[00:00:37]

the first question to answer is whether a planet can actually support life.[00:00:44]

in our own solar system, for example, venus is far too hot and mars is far too cold to support life.[00:00:50]

only the earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.[00:01:00]

whether a planet can support life depends on the size and brightness of its star, that is its 'sun'.[00:01:10]

imagine a star up to twenty times larger, brighter and hotter than our own sun.[00:01:19]

a planet would have to be a very long way from it to be capable of supporting life.[00:01:26]

alternatively, if the star were small, the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop.[00:01:32]

but how would we find such a planet?[00:01:43]

at present, there is no telescope in existence that is capable of detecting the presence of life.[00:01:47]

the development of such a telescope will be one of the great astronomical projects of the twenty-first century.[00:01:53]

it is impossible to look for life on another planet using earth-based telescopes.[00:02:01]

our own warm atmosphere and the heat generated by the telescope would make it impossible to detect objects as small as planets.[00:02:06]

even a telescope in orbit round the earth, like the very successful hubble telescope, would not be suitable because of the dust particles in our solar system.[00:02:16]

a telescope would have to be as far away as the planet jupiter to look for life in outer space,[00:02:27]

because the dust becomes thinner the further we travel towards the outer edges of our own solar system.[00:02:34]

once we detected a planet, we would have to find a way of blotting out the light from its star,[00:02:41]

so that we would be able to 'see' the planet properly and analyse its atmosphere.[00:02:47]

in the first instance, we would be looking for plant life, rather than 'little green men'.[00:02:52]

the life forms most likely to develop on a planet would be bacteria.[00:02:59]

it is bacteria that have generated the oxygen we breathe on earth.[00:03:04]

for most of the earth's history they have been the only form of life on our planet.[00:03:09]

as earth-dwellers, we always cherish the hope that we will be visited by little green men and that we will be able to communicate with them.[00:03:15]

but this hope is always in the realms of science fiction.[00:03:25]

if we were able to discover lowly forms of life like bacteria on another planet, it would completely change our view of ourselves.[00:03:29]

as daniel goldin of nasa observed, 'finding life elsewhere would change everything.[00:03:38]

no human endeavor or thought would be unchanged by it.'[00:03:45]