Around 4.5 billion years ago, something the size of Mars collided with a newly formed Earth, to colossal effect.
大約45億年前，火星大小的東西與新形成的地球相撞，產生了巨大的影響。
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.
這個物體不僅被認為已經與地球融合併為它的生命做好了準備，而且它還破壞了一大塊後來成為月球的東西。
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.
這個故事被稱為巨型撞擊假說；火星大小的物體叫做Theia；現在，科學家們第一次相信他們在月球上發現了Theia的蹤跡。
The giant-impact hypothesis has been the favoured model for explaining the formation of the Moon for years.
多年來，巨型撞擊假說一直是解釋月球形成的最受歡迎的模型。
"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.
新墨西哥大學(University of New墨西哥)的研究人員在論文中寫道，“這個模型能夠解釋阿波羅任務返回的樣本當時的觀測結果，包括月球相對於地球的低鐵含量，揮發物的損耗和難熔元素的富集，同時避免了之前月球起源理論的大部分陷阱。”
But there was one big spanner stuck in the works.
但有一個大扳手卡在作品中。
Models predicted that around 70 to 90 percent of the Moon should have been made up of mooshed and reformed Theia.
模型預測，月球的70%到90%應該是由moohouse和改造後的Theia組成的。
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，阿波羅宇航員收集的月球樣品中的氧同位素與陸地氧同位素非常相似-與太陽系其他物體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.
一種可能的解釋是，地球和Theia一開始就有相似的成分。
Another is that everything got completely mixed during the impact, which, according to simulations, isn't very likely.
另一個原因是，在撞擊期間，所有的東西都完全混合在一起，根據模擬，這是不太可能的。
Furthermore, the odds of Theia having a similar composition to Earth - as far as oxygen isotopes go - are actually extremely small.
此外，Theia具有與地球相似的成分-就氧同位素而言-的可能性實際上非常小。
Which means that, if the Moon is mostly Theia, its oxygen isotopes should be different from Earth's oxygen isotopes.
這意味著，如果月球主要是Theia，它的氧同位素應該不同於地球的氧同位素。
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