Scale: 1 pixel = approximately 4.7 km. 10-degree grid; Lambert Azimuthal Equal Area Projection, Center 40S 000E
|Copernican: Beginning with the formation of the
bright crater Copernicus, about 1.1 Ga. Formation of bright ray
Eratosthenian: Begins with the formation of the crater Eratosthenes. Fresh but non-rayed craters and late mare eruptions. 1.1 to 3.1 Ga.
Imbrian: Begins with the formation of the Imbrium Basin. Includes most mare eruptions. 3.1 to 3.8 Ga.
Nectarian: Begins with the formation of the Nectaris Basin, and includes most of the major impact basin events. 3.8 to 3.9 Ga.
pre-Nectarian: Before 3.9 Ga
The southern highlands of the lunar near side are ancient light terra made principally of anorthosite. This extensive layer of anorthosite is the principal evidence for the Moon having an early magma ocean in which dense ferromagnesian minerals sank and light feldspars rose. It is tempting to suggest that Earth's anorthosites originated the same way and are remnants of a terrestrial magma ocean, but they are far too young. Terrestrial anorthosites probably formed by density segregation in much smaller magma bodies.
Near the center of this map is the bright crater Tycho, youngest and most prominent major ray crater on the Moon. Samples of Tycho ray material were collected during the Apollo 17 mission and were dated as 108 million years old.
The odd swirling pattern around the south pole on the shaded relief maps is an artifact of the computer shading process. Illumination is from the northeast (typical on shaded relief maps) but directions are defined in terms of local coordinates, so the illumination direction changes rapidly close to the pole.
Created 11 April 2014, Last Update
12 March 2015
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