noun
several hundred million years
Refers to a very long span or age measured in hundreds of millions of years; common in geology, evolution, astronomy, and other scientific or historical contexts.
この岩石は数億年かけてできた。
This rock formed over several hundred million years.
生命の進化には数億年という時間がかかった。
The evolution of life took several hundred million years.
Means several billion years; it indicates a larger time scale than 数億年.
Means how many hundreds of millions of years or many hundreds of millions of years, depending on context; 数億年 specifically means several hundred million years.
A transparent compound of 数億, meaning several hundred million, and 年, meaning year.