natural isotopic abundance

例句：

1. 1. Thenatural isotopic abundance of the element inthe sample is very low.
   样品中该元素的天然同位素丰度非常低。
2. 2.The study of natural isotopic abundance canhelp us understand the origin of life onEarth.
   研究天然同位素丰度可以帮助我们了解地球上生命的起源。
3. 3. The natural isotopic abundance of carbon-14 inthe atmosphere is a key factor in determiningthe age of the Earth.
   大气中碳-14的天然同位素丰度是确定地球年龄的关键因素。