新概念英語第三冊(含lrc文本)Lesson 55 From the earth: Greetings

[ti:δ?] [ar:] [al:] [by:https://www.lrc.com.cn] [00:02.29]Lesson 55 [00:05.00]From the earth: Greetings [00:13.31]Which life forms are most likely to develop on a distant planet? [00:20.83]Recent developments in astronomy [00:23.10]have made it possible to detect planets in our own Milky Way and in other galaxies. [00:29.85]This is a major achievement because,in relative terms, [00:33.81]planets are very small and do not emit light. [00:38.52]Finding planets is proving hard enough, [00:41.52]but finding life on them will prove infinitely more difficult. [00:46.56]The first question to answer is whether a planet can actually support life. [00:52.65]In our own solar system,for example, [00:55.15]Venus is far to hot and Mars is far too cold to support life. [01:02.85]Only the Earth provides ideal conditions,and even here [01:07.24]it has taken more than four billion years for plant and animal life to evolve. [01:14.44]Whether a planet can support life [01:16.65]depends on the size and brightness of its star,that is its 'sun' [01:23.07]Imagine a star up to twenty times larger,brighter and hotter than our own sun. [01:30.54]A planet would have to be a very long way from it to be capable of supporting life. [01:37.10]Alternatively,if the star were small, [01:39.92]the life-supporting planet would have to have a close orbit round it [01:44.17]and also provide the perfect conditions for life forms to develop. [01:49.58]But how would we find such a planet? [01:52.83]At present,there is no telescope in existence [01:55.97]that is capable of detecting the presence of life. [01:59.90]The development of such a telescope [02:01.78]will be one of the great astronomical projects of the 21st century. [02:08.23]It is impossible to look for life on another planet using earth-based telescopes [02:13.96]Our own warm atmosphere and the heat generated by the telescope [02:18.55]would make it impossible to detect objects as small as planets. [02:23.45]Even a telescope in orbit round the earth, [02:26.24]like the very successful Hubble telescope, [02:29.48]would not be suitable because of the dust particles in our solar system. [02:35.07]A telescope would have to be as far away as the planet Jupiter [02:39.62]to look for life in outer space, [02:42.08]because the dust becomes thinner [02:43.98]the further we travel towards the outer edges of our own solar system. [02:49.56]Once we detected a planet, [02:51.37]we would have to find a way of blotting out the light from its star, [02:55.62]so that we would be able to 'see' the planet properly and analyse its atmosphere [03:01.87]In the first instance,we would be looking for plant life,rather than 'little green men [03:08.84]The life forms most likely to develop on a planet would be bacteria. [03:14.62]It is bacteria that have generated the oxygen we breathe on earth. [03:19.66]For most of the earth's history [03:21.41]they have been the only form of life on our planet. [03:25.36]As Earth-dwellers, [03:26.70]we always cherish the hope that we will be visited by little green men [03:31.71]and that we will be able to communicate with them. [03:34.95]But this hope is always in the realms of science fiction. [03:39.34]If we were able to discover lowly forms of life like bacteria on another planet, [03:44.89]it would completely change our view of ourselves. [03:49.36]As Daniel Goldin of NASA observed, [03:53.05]'Finding life elsewhere would change everything. [03:56.84]No human endeavour or thought would be unchanged by it.'

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