Lunar geologic timescale

The lunar geologic timescale (or perhaps more properly the selenologic 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. The majority of datable lunar samples are basalts of Imbrian age. Samples from before and after this period are less abundant, and the older samples have been affected by violent impact events that make precise radiometric age determination difficult.

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.

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Period = from:-4550 till:0TimeAxis = orientation:horizontalScaleMajor = unit:year increment:500 start:-4500ScaleMinor = unit:year increment:100 start:-4500

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text:Copernician from:-1100 till:0 text:Eratosthenian from:-3200 till:-1100 text:Upper_Imbrian from:-3800 till:-3200 text:Lower~Imbrian from:-3850 till:-3800 shift:(0,25) text:Nectarian from:-3920 till:-3850 shift:(0,5) from:start till:-3920 text:Pre-Nectarian

See also

* Geology of the Moon

References

* A general introduction at Purdue University