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.
This rock formed over several hundred million years.
The evolution of life took several hundred million years.
This rock layer was formed several hundred million years ago.
The Earth has a history spanning several hundred million years.
It took several hundred million years for this mountain range to form.
Means several million years, a much shorter scale than 数億年.
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.