Lunar geologic periods Lunar geologic periods The Copernician Period in the lunar geologic timescale runs from approximately 1100 million years ago to the present day. It encompasses the era during which the Moon's bright- rayed craters were formed, of which the crater Copernicus is the most prominent example. The date of this crater's formation marks the beginning of the Copernician Period. ...more on Wikipedia about "Copernician"
The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, whose formation marks the beginning of this period. The formation of the crater Copernicus marks its end, and the beginning of the subsequent Copernician Period. ...more on Wikipedia about "Eratosthenian"
In the Lunar geologic timescale, the Lower Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. The impact which created the Mare Imbrium basin occurred at the start of the epoch, and it represents the period during which the newer large basins were formed. These filled with basalt largely during the following Upper Imbrian epoch. The Lower Imbriam was preceded by the Nectarian. ...more on Wikipedia about "Lower Imbrian"
The lunar geologic timescale (or perhaps more properly the selenologic timescale) divides the history of Earth's Moon into six generally recognized geologic periods: ...more on Wikipedia about "Lunar geologic timescale"
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin was formed by a large impact event. Ejecta from Nectaris forms the upper part of the densely cratered terrain found in lunar highlands. ...more on Wikipedia about "Nectarian"
The Pre-Nectarian Period of the lunar geologic timescale runs from 4550 million years ago (the time of the initial formation of the Moon) to 3920 million years ago, when the Nectaris Basin was formed by a large impact. Pre-Nectarian rocks are mostly composed of highlands material, heavily churned by subsequent impacts. ...more on Wikipedia about "Pre-Nectarian"
In the Lunar geologic timescale, the Upper Imbrian epoch occurred between 3800 million years ago to about 3200 million years ago. It was the period during which the mantle below the Lunar basins partially melted and filled them with basalt. The melting is thought to have occurred because the impacts thinned the overlying rock - either causing the mantle to rise because of the reduced pressure on it, bringing molten material closer to the surface; or the top melting as heat flowed upwards through the mantle because of the reduced thermal insulation on top of it. ...more on Wikipedia about "Upper Imbrian"
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