The researchers base their argument on the ratios of light to heavy nitrogen isotopes in ancient rocks from Australia.

研究人员是根据澳大利亚古老岩石中重氮同位素光的比率所得出的结论。

That carbon atom can be either the " light" isotope, with six neutrons in its nucleus, or the heavy isotope, which has seven.

该碳原子可以是“轻”同位素（其原子核中有六个中子），也可以是重同位素（其原子核中有七个中子）。

The first step on the journey to helium—fusing two individual protons together to form a heavy isotope of hydrogen called deuterium (a proton and a neutron)—is reckoned to take, on average, 9bn years.

氦气之旅的第一步——将两个单独的质子融合在一起形成一种称为氘的重氢同位素（一个质子和一个中子）——估计平均需要 90 亿年。