20世纪80年代时科学家们认为地球周期性的生物灭绝可能是由遥远太空的涅墨西斯星球造成的，该星球和太阳很相似。
In the 1980s scientists believed that Earth's regular extinctions could be the result of a distant dark twin of the Sun, called Nemesis.
生物节律：由生物钟控制的周期性的生理上的或行为上的变化。昼夜节律就是一个很好的例子。
Biorhythm a periodic physiological or behavioral change that is controlled by a biological clock. Circadian rhythms are an example.
假如地球磁极逆转而造成生物大量灭尽，那就不难表明为何每隔一段时间，使地球文明周期性的毁灭。
If the Earth's magnetic pole reversal caused by biological extinction, it is not difficult to explain why from time to time, so that the periodic destruction of the Earth civilization.
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