And that creates an interesting problem in understanding planetary evolution.

引出了一个关于行星演化的有趣问题。

After 2 billion years of planetary and biological evolution, the first plants and animals emerged from water onto land.

经过超过20亿年的不断进化最初的两栖射生物开始爬上陆地。

But this has not always been the case, and we know this because ancient rocks have recorded the pivotal moments in Earth's planetary evolution.

但情况并非总是如此，我们之所以知道这一点， 是因为古代岩石记录了地​​球行星演化的关键时刻。