继氢之后，氦作为宇宙第二大常见元素，在宇宙大爆炸时期大量产生。
After hydrogen, helium is the second most common element in the universe, with the bulk of it formed during the big bang.
主流的理论假设认为，月球是大爆炸时期一火星大小的物体猛烈撞击地球而形成的。
The prevailing hypothesis is that the moon was formed from a giant impact event, when a Mars-sized object slammed into Earth.
这种膨胀正好就是我们的宇宙在大爆炸时期所发生的事情，当时一小块物质膨胀成了现在成熟的宇宙。
Such expansion was precisely what our universe did in the Big Bang, when it suddenly exploded from a tiny clump of matter into a fully-fledged cosmos.
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