Lunar geologic timescale
From Wikipedia, the free encyclopedia
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 dating 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.
[edit] See also
[edit] References
- Geologic History of the Moon, Don Wilhelms, U.S. Geological Survey Professional Paper 1348, 1987.
- Linda Martel (September 28, 2004). Lunar Crater Rays Point to a New Lunar Time Scale.
 |
| General: Phases of the Moon · Solar eclipse · Lunar eclipse · Orbit of the Moon · Tides · Near and Far sides of the Moon |
| Lunar science: Moon rocks · Geology · Lunar mare · Lunar geologic timescale · Lunar meteorites · KREEP · Giant impact theory |
| Exploration: Exploration of the Moon · Project Apollo · Robotic exploration · Future missions · Lunar colonization |
| See also solar system, natural satellite, and impact craters. |
