Time Scales

Updated About encyclopedia.com content Print Article Share Article
views updated

Time Scales

Geologic Time‐Scale

Eon/Eonothem

Era/Erathem

Sub‐era

Period/System

Epoch/Series

Starting Ma

PHANEROZOIC

Cenozoic

Quaternary

Pleistogene

Holocene

0.01

Pleistocene

1.8

Tertiary

Neogene

Pliocene

5.2

Miocene

23.3

Palaeogene

Oligocene

35.4

Eocene

56.5

Palaeocene

65

Mesozoic

Cretaceous

145.6

Jurassic

208

Triassic

245

Palaeozoic

Upper Palaeozoic

Permian

290

Carboniferous

362.5

Devonian

408.5

Lower Palaeozoic

Silurian

439

Ordovician

510

Cambrian

570

PROTEROZOIC

PRECAMBRIAN

2500

ARCHAEAN

4000

PRISCOAN

4600

(After Harland et al., 1989)

Geologic Time‐Scale

Eon/Eonothem

Era/Erathem

Sub‐era

Period/System

Epoch/Series

Starting Ma

PHANEROZOIC

Cenozoic

Quaternary

Pleistogene

Holocene

0.01

Pleistocene

1.64

Tertiary

Neogene

Pliocene

5.2

Miocene

23.3

Palaeogene

Oligocene

35.4

Eocene

56.5

Palaeocene

65

Mesozoic

Cretaceous

145.6

Jurassic

208

Triassic

245

Palaeozoic

Upper Palaeozoic

Permian

290

Carboniferous

362.5

Devonian

408.5

Lower Palaeozoic

Silurian

439

Ordovician

510

Cambrian

570

PROTEROZOIC

PRECAMBRIAN

2500

ARCHAEAN

4000

PRISCOAN

4600

(After Harland et al., 1989)

Lunar Time‐Scale

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

System

Events

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.

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 Procellarum basin (before 3.92–4.2? billion years)