Related Clues:

• Holocene, e.g.
• Geological span
• History unit
• Distinctive period
• Loooong time
• It's comprised of ages and ages
• Heck of a long time
• Really big span
• Years and years on end
• Unimaginably long time
• Long time division
• Geological time span
• Memorable era
• Span longer than an era
• Exceedingly long time