Most experts believe a huge impact early in Earth's history ejected material into space that became the moon.

绝大多数的专家都相信，月球是在一个巨大行星与早期地球碰撞过程中所产生的碎石组成的。

youdao

He said about one hundred kilograms of water had been found in the material ejected by the moon crash.

VOA: special.2009.12.30

When the explosion occurred, the ejected material would have traveled unimpeded by gas and dust and spread out quickly.

FORBES: NASA Reveals the Mysteries of the First Known Supernova