Lunar geologic timescale

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

The values for these dates remain in some dispute, as the divisions are based on the dates when various significant lunar geological events occurred and it is difficult to pinpoint them exactly.

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.