Geologic Time
Geologic time - the total time from the formation of the earth to the present day.
One hundred years seems like a long time. Millions, even billions of years seem impossible
to imagine. That's why scientists have divided the geologic time scale into four different
eras:
1. Precambrian
2. Paleozoic
3. Mesozoic
4. Cenozoic
 The geologic age of the earth is estimated to be 4.6 billion years.
 This long period of time has been broken into four eras and eras have been divided
into shorter periods.
 The oldest rock in Canada are found in the Canadian Shield.
 They are estimated to be over 2.5 billion years old and were formed during the
Precambrian era.
 It is hard to know the actual age of the rocks because they have undergone heat,
pressure, and weathering changes.
ACTIVITY
1. Complete the time line on the next page using the diagram displayed on the overhead.
Use different colours to differentiate between the four eras.
2. How many periods has there been since the formation of the earth? ___________
3a. Which period lasted the longest? _________________________
b. How many years did it last?
_________________________
4. What number would you find at the very bottom of the time line? Why?
The Four Eras of Geologic Time
ERA
Cenozoic
Mesozoic
PERIOD
Quaternary
Tertiary
Paleozoic
YEARS AGO
11 000
65 million
Cretaceous
135 million
Jurassic
195 million
Triassic
230 million
Permian
Precambrian
280 million
Pennsylvanian
310 million
Mississippian
345 million
Devonian
395 million
Silurian
435 million
Ordovician
500 million
Cambrian
600 million
Precambrian
The Four Eras of Geologic Time
ERA
Cenozoic
Mesozoic
PERIOD
Quaternary
Tertiary
Paleozoic
YEARS AGO
11 000
65 million
Cretaceous
135 million
Jurassic
195 million
Triassic
230 million
Permian
Precambrian
280 million
Pennsylvanian
310 million
Mississippian
345 million
Devonian
395 million
Silurian
435 million
Ordovician
500 million
Cambrian
600 million
Precambrian