Time Scale of the Earth

EON ERA PERIOD EPOCH  BEGINNING  MAJOR EVENTS GLOBAL
EXTINCTION
EVENT
P
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R
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Z
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Cenozoic
(age of  mammals)
  Quaternary Holocene 11,700 present climate; only modern humans  
Pleistocene 2,600,000 recent ice ages; various human species
Tertiary Pliocene 5,300,000 near-human species and other near-modern mammals
Miocene 23,000,000 apes flourish; savanna grazing animals evolve
Oligocene 33,900,000 monkeys, apes, and other mammal families evolve
Eocene 55,800,000 prosimians flourish; possible early monkeys
Paleocene     65,500,000 earliest primates (proto-prosimians)
Mesozoic
(age of reptiles)
Cretaceous   145,500,000 archaic mammals and birds begin to replace dinosaurs; first flowering plants 65,500,000
(76% of species lost)
Jurassic 199,600,000 dinosaurs dominant; primitive mammals spread; toothed birds
Triassic   251,000,000 first dinosaurs and first egg-laying mammals; vast forests of ferns, conifers, and cycads 200,000,000
(80% of species lost)
Paleozoic
  (ancient life forms)
Permian filler.gif (42 bytes) 299,000,000 spread of reptiles and insects; first mammal-like reptiles

251,000,000
(95-96% of species lost: earth's largest mass extinction)

Carboniferous   359,200,000 amphibians dominant; forests flourish; reptiles and modern insects appear
Devonian    416,000,000 fish dominant; amphibians appear; first forests

360,000,000
(83% of species lost)

Silurian   443,700,000 fish with jaws; first air breathing animals
Ordovician   488,300,000 invertebrates dominant; first vertebrates (jawless fish); first land plants 444,000,000
(85% of species lost)
Cambrian   542,000,000 explosion of life forms; invertebrates dominant (worms, jellyfish, trilobites, etc.) 488,000,000?
P
R
E
C
A
M
B
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M
Proterozoic
(earliest life forms)
filler.gif (42 bytes) filler.gif (42 bytes) 3,000,000,000 protozoa, sponges, and algae; oxygen begins to accumulate in the atmosphere
3,500,000,000 first clear evidence of  life (one celled bacteria)
Azoic
(no life forms)
filler.gif (42 bytes) filler.gif (42 bytes) 4,540,000,000 origin of the earth

"BEGINNING" refers to the number of years before the present to the beginning of the Era, Period, or Epoch. In some cases, the dates differ slightly from those in other geologic time scales.  Most notably, the origin of the earth is sometimes rounded off to 4.5 or 6 billion years ago.

[Source: John Relethford (2013), The Human Species: An Introduction to Biological Anthropology, 9th ed.; Robert Jurmain et al. (2010), Introduction to Physical Anthropology, 2009-2010 ed.; Philip Stein and Bruce Rowe (2011), Physical Anthropology, 10th ed.; and Richard Harter (1998),Changing Views of the History of the Earth]
 

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Copyright 1999-2012 by Dennis O'Neil. All rights reserved.