What are the dates/years for each Disney era?

What are the specific (or rough) dates/years for each Disney era?

For instance, I know it's said that the Disney Renaissance is from
1989-1999, starting with The Little Mermaid and ending with Tarzan.

So, I was wondering if there were set dates for the following eras.

Classic Disney
Disney's Dark Ages
The Disney Renaissance
Disney's Modern Age