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Time-Scales

Source:
A Dictionary of Geology and Earth Sciences

Time-Scales

Time-Scales

Lunar Time-Scale

Stratigraphic mapping of the lunar surface has established the following Systems, in order of increasing age:

System

Events

Copernican

Young ray craters (younger than about one billion years)

Eratosthenian

Older post-mare craters (about 1–3 billion years)

Imbrian

Main mare basalt flooding, preceded by formation of the Imbrium and Orientale basins (3–3.85 billion years)

Pre-Imbrian:

Nectarian

Formation of 11 major impact basins preceded by the Nectaris basin (3.85–3.92 billion years)

Pre-Nectarian

Formation of about 30 impact basins preceded by the Procellarumbasin (before 3.92–4.2? billion years)

The crystallization of the anorthositic lunar highland crust has been dated at 4.44 billion years. This event closely followed the formation of the Moon.

Note that the term ‘Procellarum System‘, to encompass the main period of mare lava flooding, has been abandoned.

Martian (Areological) Time-Scale

Epoch

Absolute age (Gy)

Absolute age (Gy)

(Hartmann–Tanaka Model)

(Neukum–Wise Model)

Upper Amazonian

0.25–0.00

0.70–0.00

Middle Amazonian

0.70–0.25

2.50–0.70

Lower Amazonian

1.80–0.70

3.55–2.50

Upper Hesperian

3.10–1.80

3.70–3.55

Lower Hesperian

3.50–3.10

3.80–3.70

Upper Noachian

3.85–3.50

4.30–3.80

Middle Noachian

3.92–3.85

4.50–4.30

Lower Noachian

4.60–3.92

4.60–4.50

(These represent two different models published by the University of Arizona Press)

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