Around 4.5 billion years ago, something the size of Mars collided with a newly formed Earth, to colossal effect.
大约45亿年前，火星大小的东西与新形成的地球相撞，产生了巨大的影响。
This object is not only thought to have fused with Earth and primed it for life, it also broke off a large chunk that went on to become the Moon.
这个物体不仅被认为已经与地球融合并为它的生命做好了准备，而且它还破坏了一大块后来成为月球的东西。
This story is known as the giant-impact hypothesis; the Mars-sized object is called Theia; and now, for the first time, scientists believe they've found traces of Theia in the Moon.
这个故事被称为巨型撞击假说；火星大小的物体叫做Theia；现在，科学家们第一次相信他们在月球上发现了Theia的踪迹。
The giant-impact hypothesis has been the favoured model for explaining the formation of the Moon for years.
多年来，巨型撞击假说一直是解释月球形成的最受欢迎的模型。
"This model was capable of accounting for the then-recent observations from samples returned by the Apollo missions, which included the Moon's low iron content relative to Earth, depletion in volatiles and enrichment in refractory elements, while avoiding most of the pitfalls of previous lunar origin theories," researchers from the University of New Mexico wrote in their paper.
新墨西哥大学(University of New墨西哥)的研究人员在论文中写道，“这个模型能够解释阿波罗任务返回的样本当时的观测结果，包括月球相对于地球的低铁含量，挥发物的损耗和难熔元素的富集，同时避免了之前月球起源理论的大部分陷阱。”
But there was one big spanner stuck in the works.
但有一个大扳手卡在作品中。
Models predicted that around 70 to 90 percent of the Moon should have been made up of mooshed and reformed Theia.
模型预测，月球的70%到90%应该是由moohouse和改造后的Theia组成的。
However, oxygen isotopes in lunar samples collected by Apollo astronauts were very similar to terrestrial oxygen isotopes - and very different from oxygen isotopes on other Solar System objects.
然而，阿波罗宇航员收集的月球样品中的氧同位素与陆地氧同位素非常相似-与太阳系其他物体上的氧同位素有很大不同。
One possible explanation is that Earth and Theia had similar compositions to start with.
一种可能的解释是，地球和Theia一开始就有相似的成分。
Another is that everything got completely mixed during the impact, which, according to simulations, isn't very likely.
另一个原因是，在撞击期间，所有的东西都完全混合在一起，根据模拟，这是不太可能的。
Furthermore, the odds of Theia having a similar composition to Earth - as far as oxygen isotopes go - are actually extremely small.
此外，Theia具有与地球相似的成分-就氧同位素而言-的可能性实际上非常小。
Which means that, if the Moon is mostly Theia, its oxygen isotopes should be different from Earth's oxygen isotopes.
这意味着，如果月球主要是Theia，它的氧同位素应该不同于地球的氧同位素。
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