现在，当彗星撞地球，会发生什么？

Now, when the comet hit the earth, what would happen?

youdao

行星撞地球这种事每隔一亿年左右才会发生一次。

They hit the Earth roughly every hundred million years or so.

youdao

当然还有不少其他的理论，比如由于地震或全球变暖导致的海底的甲烷气体释放，或者是小行星撞地球。

Other theories include a catastrophic release of methane gas stored under the seabed, triggered by earthquakes or global warming, or a massive asteroid impact.

youdao