The lunar geologic timescale divides the history of Earth's Moon into six generally recognized geologic periods:
- Copernician Period : -1100 MY to present
- Eratosthenian Period : -3200 MY to -1100 MY
- Upper Imbrian Epoch : -3800 MY to -3200 MY
- Lower Imbrian Epoch : -3850 MY to -3800 MY
- Nectarian Epoch : -3920 MY to -3850 MY
- Pre-Nectarian Epoch: -4550 MY to -3920 MY
In many lunar highland regions, planetologists cannot currently distinguish between Nectarian and Pre-Nectarian materials. These deposits are called Pre-Imbrian age materials, which encompasses both time periods.