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The Earth. on the other hand, was born only 4.6 billion years ago. That result comes from measurements of the ages of meteorites and from the ages of the moon rocks brought back by the Apollo astronauts. Since meteorites and the moon are relatively unchanged samples of solar-system material, dating back to the birth of the planets, their age is thought to give a good estimate of the age of the Earth.
而地球仅诞生于46亿年前。这个结论是通过检测陨星的年龄和阿波罗号宇航员带回的月球岩石的年龄得出的。由于陨星和月球是行星诞生的时候太阳系物质的相对说来未发生变化的样本，所以人们认为，它们的年龄为估计地球的年龄提供了很好的参照。
Thus, many planets circling distant stars are 5, 10 and even 15 billion years older than the Earth.It follows that the Earth is a very recent arrival in the cosmic family of planets, and man is among the youngest denizens of the Universe.
这样算来，许多围绕遥远的恒星运转的行星要比地球古老50亿、100亿年乃至150亿年。由此可见，地球是宇宙行星系中一个相当晚的后来者，而人类则是宇宙中最年轻的居民之一。
Of course, the fact that life elsewhere is older than man does not necessarily mean that this life is more intelligent. However, other scientific evidence suggests that this is likely to be the case. Throughout the last 300 million years of life on Earth, only one seemingly universal trend can be discerned in evolution; this is the trend toward greater intelligence. Since before the fishes left the water, the most intelligent form of life present on Earth in each era has been the rootstock out of which new and still more intelligent forms have evolved. The line of increasing intelligence stretches unbroken from the fishes to the reptiles to the mammals, the primates and man. Apparently, intelligence -- which permits a flexible response to changing conditions -- has a greater survival value than any other single trait.
当然，别处的生命比人类年长的事实并不一定意味着那些生命具有更高的智慧。然而，其他科学证据表明，情况可能确实如此。从地球上的生命经历的最近3亿年间，仅能看出一个像似普遍的进化规律，这就是向更高智慧发展的趋势。早自鱼类离开水之前开始，地球上每个时期出现的智能最高的生命形式，总是演化新的具有更高智慧的生命形式的来源。智慧不断提高像一条线从未间断过，它从鱼类延伸到爬行动物，再延伸到哺乳动物、灵长目动物和人类。显然，智慧——它使对不断变化的环境作出灵活反应成为可能——与其他任何单个特征相比，对于生存具有更高的价值。
