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Geologist have divided the Moon's history into five distinct eras.  The first era, the Pre-Nectarian era, lasted from about the origin of the Moon to 4.6 billion years ago.  The era was marked by the formation of the Moon.  Theories have suggested that the Moon's core was either broken from Earth by impact or captured by Earth, causing it to grow in size.   The next even that occurred, was the differentiation of the Moon, and the formation of its anorthosite crust.  It is likely that sufficient amounts of heat energy were released from early impacts that the Moon was covered with a magma ocean.  The mineral plagioclase then crystallized in this magma, floated to the top, and formed the anorthosite crust.  Olivine and pyroxene crystallized in the surface and sank, and later provided material for the magma that flooded the mare basins. 

The Nectarian ear lasted from 3.9 billion ears to 3.85 billion years ago.  It was named after the impact crated Nectaris basin during the beginning of this era.  This impact then scattered ejecta, consists f the Jassen formation.  This formation and other impact related strata are important because they have been able to be identified over large portions of the Moons are are used to determining the ages of rock layers.  Also during this era, 10 other impact basins where formed.

The third era, the Imbrian era, lasted from 3.85 billion years to 3.2 billion years ago.  At the beginning of the era, the Imbrian basin was formed, which covers most of the Fra Mauro formation.  One of the last basins to be formed waste that of the Orientale basin.  This era also saw the beginning of time where maria was formed as erupting lava filled many impact basins.    About 2/3 of the mara lava was extruded ruing this era.

The Eratosthenian era covered about 3.2 billion years to 1.0 billion year ago.  Volcanic activity continued during this time, and the remainder of the mare rocks were formed.  This era has been named after one of the Moon's more conspicuous craters.  Craters formed during this time lack light-coloured rays but have well0preseved secondary craters.

The Copernican era lasts from the past billion years until the present.  Copernican craters, after which this era was named, have been identified due  to their bright, conspicuous rays.  Throughout this time the Moon was most likely volcanically dead. 

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