Related Clues:

• Momentous era
• Countless centuries
• Awfully long time
• Geologic period
• Unbelievably long time
• It goes on and on
• Noteworthy time
• Geologic time
• Date of reference
• Significant period
• Longish time span
• L-o-n-g time period
• Period of note
• A really long time
• Long period