Lesson 55 From the earth: Greetings
Listen to the tape then answer the question below. Which life forms are most likely to develop on a distant planet? Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies. This is a major achievement because, in relative terms, planets are very small and do not emit light. Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult. The first question to answer is whether a planet can actually support life. In our own solar system, for example, Venus is far too hot and Mars is far too cold to support life. Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.

来自地球的问候
听录音，然后回答以下问题。 什么样的生命形式最有可能在一颗遥远的星球上繁衍？ 天文学方面最新发展使得我们能够在银河系和其他星系发现行星。 这是一个重要的成就，因为相对来说，行星很小，而且也不发光。 寻找行星证明相当困难，但是要在行星上发现生命会变得无比艰难。 第一个需要解答的问题是一颗行星是否有能够维持生命的条件。 举例来说，在我们的太阳系里，对于生命来说，金星的温度太高，而火星的温度则太低。 只有地球提供了理想的条件，而即使在这里，植物和动物的进化也用了40亿年的时间。