million years ago的意思是：几百万年前。
短语：
sixty million years ago 六千万年前
Many million years ago 在数百万年前
cretaceous period million years ago 白垩纪时期
A million years ago 灯火阑珊时一百万年前
permian period million years ago 二叠纪时期
例句：
1.When plants first made the transition ashore more than 400 million years ago, the land was barren and desolate, inhospitable to life.
4亿多年前，植物第一次向海岸上迁移时，陆地上荒凉而贫瘠，并非生命宜居之地。
2.Eighty million years ago, dinosaurs ruled the earth.
八千万年前，地球是恐龙的天下。
3.South America and Africa separated 200 million years ago.
南美洲和非洲于2亿年前分离。
4.South America separated from Africa 200 million years ago.
2亿年前南美洲和非洲分离。
5.Twenty million years ago, Idaho was populated by dense primordial forest.
两千万年前，爱达荷州遍布着茂密的原始森林。
6.It has been suggested that mammals took over from dinosaurs 65 million years ago.
有人提出哺乳动物是在6 500万年前取代恐龙的。
