Copernician
Encyclopedia
The Copernican Period in the lunar geologic timescale
runs from approximately 1.1 billion years ago to the present day. The base of the Copernican period is defined by impact craters that possess bright optically immature ray system
s. The crater Copernicus
is a prominent example of rayed crater, but it does not mark the base of the Copernican period. No mare basalts are known to have erupted within the Copernican period, and for this reason, the Moon's internal geologic activity is thought to have effectively ceased by this time.
processes. Operationally, this period was originally defined as the time at which impact craters "lost" their bright ray system
s. This definition, however, has recently been subjected to some criticism as some crater rays are bright for compositional reasons that are unrelated to the amount of space weathering they have incurred. In particular, if the ejecta from a crater formed in the highlands (which is composed of bright anorthositic materials) is deposited on the low albedo mare, it will remain bright even after being space weathered.
era of the Proterozoic
eon and the whole of the Phanerozoic
eon. So, while animal life bloomed on Earth, the Moon's geologic activity was coming to an end.
Lunar geologic timescale
The lunar geological timescale divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian , Nectarian, and Pre-Nectarian...
runs from approximately 1.1 billion years ago to the present day. The base of the Copernican period is defined by impact craters that possess bright optically immature ray system
Ray system
A ray system comprises radial streaks of fine ejecta thrown out during the formation of an impact crater, looking a bit like many thin spokes coming from the hub of a wheel. The rays can extend for lengths up to several times the diameter of their originating crater, and are often accompanied by...
s. The crater Copernicus
Copernicus (lunar crater)
Copernicus is a prominent lunar impact crater named after the astronomer Nicolaus Copernicus, located in eastern Oceanus Procellarum. It is estimated to be about 800 million years old, and typifies craters that formed during the Copernican period in that it has a prominent ray system.-...
is a prominent example of rayed crater, but it does not mark the base of the Copernican period. No mare basalts are known to have erupted within the Copernican period, and for this reason, the Moon's internal geologic activity is thought to have effectively ceased by this time.
Definition
The base of the Copernican period is defined based on the recognition that freshly excavated materials on the lunar surface are generally "bright" and that they become darker over time as a result of space weatheringSpace weathering
Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment. Airless bodies incur many weathering processes:* collisions of galactic cosmic rays and solar cosmic rays,* irradiation, implantation, and sputtering from solar wind...
processes. Operationally, this period was originally defined as the time at which impact craters "lost" their bright ray system
Ray system
A ray system comprises radial streaks of fine ejecta thrown out during the formation of an impact crater, looking a bit like many thin spokes coming from the hub of a wheel. The rays can extend for lengths up to several times the diameter of their originating crater, and are often accompanied by...
s. This definition, however, has recently been subjected to some criticism as some crater rays are bright for compositional reasons that are unrelated to the amount of space weathering they have incurred. In particular, if the ejecta from a crater formed in the highlands (which is composed of bright anorthositic materials) is deposited on the low albedo mare, it will remain bright even after being space weathered.
Relationship to Earth's geologic time scale
Its Earth equivalents are the NeoproterozoicNeoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
era of the Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
eon and the whole of the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
eon. So, while animal life bloomed on Earth, the Moon's geologic activity was coming to an end.