GEOLOGIC TIME SCALE NOTETAKERS
Uniformitarianism
 Earth is an always ___________________ place
 The _______________ forces of change at work today were at work in the past
 The Earth has changed ______________________ (very slow)
The Geologic Time Scale
 Shows Earth’s History divided into time units based on ____________ ___________
that existed and _______________ ________________.
 Earth is estimated to be _________ billion years old.
 Oldest living things were __________-_______________ organisms at about 3.5 billion
years.
 Humans show up only about ________________ years ago.
Division of Geologic Time
 Eons – ________________ unit
 Eras – eons are divided into eras
 _________________, ________________, _______________
 Periods – eras are divided into ______________
 Epochs – periods are divided into ______________
Precambrian Time
 The ____________________ part of Earth’s history
 About ____________ billion years long
 1st _______________ formed 3.9 billions years ago.
 1st living things appear about 3.5 billion years ago during the Precambrian; single-celled
simple organisms (_________________)
 Invertebrate (no backbone) animals show up at the _____________ of the Precambrian.
 This time ended with a global ___________ ____________.
Paleozoic Era
544 mya – 248 mya
 Means “_____________ ____________” often known as the age of ___________.
 At the beginning of this era there is an explosion of life in the ______________,
_________________ seas of the time.
 Organisms with _____________ and _______________ (backbone) form.
 Trilobites, mollusks, fish, amphibians
 Life moves onto land at the end of this era and the first ______________ and large
insects form.
 _____________________ mountains form.
 _____________________ forms.
 Largest mass extinction marks the end of this era. __________% of all life disappears
in the fossil record
 One theory is global – climate change due to massive ___________________
Mesozoic Era
248 mya – 65 mya
 Means “_____________ ____________” and often know as the age of ___________.
 ___________________ ruled the Earth
 First ____________________ plants
 First birds and ____________________
 Pangaea __________________
 Another mass _____________________ at the end of this era.
 Most excepted theory is a massive ____________________ hit the Earth causing
global-climate change.
Cenozoic Era
65 mya – present
 Means “______________ ____________” and known as the age of ______________
 Several __________ ______________
 Fossils of the 1st __________________ show up 100,000 years ago. (not very long ago
in __________________ time)
Quick Check
1. ____ is the idea that the forces that changes the Earth today are the same forces that existed in
the past.
A. Paleontology
B. Uniformitarianism
C. Cambrianism
D. Geology
2. ____ are the oldest living things thought to have first formed 3.5 billion years ago.
A. Mammals
B. Birds
C. Trilobites
D. Bacteria
3. ____ is the era dominated by life in the oceans.
A. Precambrian
B. Paleozoic
C. Mesozoic
D. Cenozoic
4. At the end of the ____ era, an asteroid hit the Earth causing mass extinction and the end of the
dinosaurs.
A. Precambrian
B. Paleozoic
C. Mesozoic
D. Cenozoic
5. Which picture shows a close representation of the geologic time scale? (draw the answer)