Related Clues:

• Eon part
• Its end is often observed
• Many many years
• Word after Reagan or Clinton
• Chronology segment
• A million millennia
• A pitcher should keep it low
• Word with ''Big Band'' or ''Reagan''
• Untold millennia
• The Phanerozoic, e.g.
• Reconstruction, e.g.
• Onetime NOW cause
• See 41 Down
• Era after era
• It's split into eras