| age
or period |
dates |
notes and main features |
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| Precambrian era
comprising the Archaean and Proterozoic eons |
4600 - 595 mya |
Origins of life, oxygen
atmosphere forms. |
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| Archaean eon (Archean
eon), also called Archaeozoic or Archeozoic |
4600 - 2500 mya |
Early part of the Precambrian,
stromatolites formed, the name means "ancient life" or
"archaic life". |
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| Proterozoic eon |
2500 - 595 mya |
Ediacaran fauna is from this
time: the name means "first life". |
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| Phanerozoic time |
595 mya - present |
All ages since the Precambrian,
once thought to be the only period with fossils. |
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| Palaeozoic era (Paleozoic
era) comprising |
595 - 250 mya |
The name
means "old life", the dates, using other criteria, can also be
found as 570 - 245 mya (million years ago). |
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| Lower Palaeozoic era |
595 - 408 mya |
Lower here in the sense of lower
in the ground than later rocks. |
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| Cambrian period |
595 - 505 mya |
Many
invertebrate groups with "hard" parts that fossilise well, named
for Cambria (Roman name for Wales), where these rocks were first noted. |
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| Ordovician period |
505 - 438 mya |
Trilobites
at their peak, all life marine, first fish appear (vertebrates), named after
the Ordovices, a tribe who once lived in north Wales. |
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| Silurian period |
435 - 408 mya |
True jawed
fish, first land plants, scorpions the first air-breathing animals, named
after the Silures, a tribe who inhabited the part of Wales where these rocks
are found (among other places). |
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| Upper Palaeozoic era |
408 - 250 mya |
Upper here reminding us that
these are the top beds of this sequence. |
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| Devonian period |
408 - 360 mya |
First amphibians, first forests,
named for Devon (southern England) where rocks of this age occur. |
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| Carboniferous period
(Divided in north America into the next two groups) |
360 - 286 mya |
Coral
reefs form limestone, swamps with conifers and ferns form most modern coal,
reptiles emerge. Named for the carbon of the coal deposits. |
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| Mississippian period (in
the USA) |
360 - 330 (?) |
The lower
part of the Carboniferous in north America: large primitive trees, flooding
of N. America, limestone laid down: uplift and folding of the Appalachian
mountains across the Mississippian and Pennsylvanian, named for the rocks of
the Mississippi Valley in the USA. |
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| Pennsylvanian period (in
the USA) |
330 (?) - 286 mya |
The upper
part of the Carboniferous in north America: abundant insects, first reptiles,
modern USA had a tropical climate, widespread swamps, providing today's US
coal sources, named for the rocks of Pennsylvania, USA. |
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| Permian period |
286 - 250 mya |
Many
invertebrate groups (including trilobites) go extinct, mammal-like reptiles
appear, reptiles diversify, named after the Perm province of Russia. |
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| Mesozoic era comprising |
250 - 65 mya |
Middle life period, may also be
dated 245 - 66 mya by other authors. |
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| Triassic period |
250 - 213 mya |
First dinosaurs, small mammals,
named after a threefold division of rocks of this age in Germany. |
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| Jurassic period |
213 - 144 mya |
Large reptiles, Archaeopteryx,
first birds, primitive mammals, named for the Jura mountains of Switzerland. |
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| Cretaceous period |
144 - 65 mya |
Dinosaurs
dominate and then go extinct, flowering plants appear. Named for the chalk
deposits of France and England. |
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| Cenozoic era comprising |
65 mya - present |
Mammals and flowering plants
become dominant. The name means "recent life". |
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| Tertiary period
comprising |
65 - 2 mya |
The third
major period, when the world's major mountain ranges developed: the old terms
"primary" and "secondary" are no longer used. |
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| Palaeocene epoch |
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65 - 55 mya |
The name means "ancient recent"(these next few
names came from the similarities of fossil molluscs to modern species!). |
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| Eocene epoch |
55 - 37 mya |
The name means "dawn
recent". |
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| Oligocene epoch |
37 - 25 mya |
The name means "few
recent" (molluscs). |
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| Miocene epoch |
25 - 5 mya |
Alps and the Himalayas formed,
the name means "lesser recent". |
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| Pliocene epoch |
5 - 2 mya |
The name means "more
recent", and Australopithecines are found, right through it. |
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| Quaternary period
comprising |
2 mya - present |
Modern
humans arise around this time, most probably with genus Homo at 2.5 mya and
humans like us in about the last 100 000 years. |
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| Pleistocene epoch |
2 mya - 10 kya |
The name means "most
recent". |
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| Holocene epoch |
10 kya - present |
The name means "whole
recent" (that is, all fossil molluscs from this time are still known as
modern species). |
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