In the pre-atomic age, people couldn't imagine the immense power brought by nuclear energy.

pre-atomic 由前缀 pre-（表示"在...之前"）和 atomic（原子的）组成。pre-atomic 意思是"原子时代之前的"。 atomic 来自名词 atom（原子）加上形容词后缀 -ic，表示"与原子有关的"。