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Chapter 15:5
Geologic Time Scale
Geologic Time Scale
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Divides Earth’s 4.6 billion year history into
parts
Our division of time:
Day  Hour  Minute  Second

Division in Geologic Time Scale:
Eon  Era  Period  Epoch
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Extinction
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Means death of every member of a species
Most paleontologists agree on five mass
extinction events in Earth’s history, but they do
not agree on the cause of those events
Precambrian Era


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Lasted from 4.6 billion years ago to 543
million years ago
First signs of life are bacteria in the water
By end of this era, animals such as jellyfish
and worms have appeared
Paleozoic Era
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
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Lasted from 543 million years ago to 248
million years ago
First era we find fossils from
By the middle of the era, we started to see
plants on land
By the end of the era, amphibians and reptiles
lived on land and there were many insects
Ended with largest mass extinction in Earth’s
history (killed about 90% of species)
Mesozoic Era

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Lasted from 248 million years ago to 65
million years ago
Known as the Age of the Reptiles because they
dominated
Divided into Triassic, Jurassic, and Cretaceous
Periods
Mesozoic Era continued

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Triassic Period – Mammals appear and the first
dinosaurs are appearing
Jurassic Period – The Age of the Dinosaur
begins and birds begin to appear towards the
end
Cretaceous Period – Dinosaurs dominate, TRex and Triceratops roam the Earth, but all
dinosaurs will have died out by the end.
Cenozoic Era
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Lasted from 65 million years ago to the present
Known as the Age of Mammals
Divided into Tertiary and Quaternary Periods
Cenozoic Era continued

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Tertiary Period- Mild climate, it is believed
that humanlike creatures began walking
upright toward the end of this period
Quaternary Period- climate turns very cold,
last ice age ends about 11,000 years ago, and
modern civilization begins