Geologic Time Scale
Lesson 4
Essential Question
Learning Objective:
Explain how geologists use the
geologic time scale to divide Earth’s
history.
Standard:
Evidence of the dynamic changes of
Earth’s surface through time is found
in geologic record.
Divide Your Parents Lives?
—  Divide your parents life into sections!!!
—  You must include at least 5 different
sections.
— Write them down and then share with
your neighbor and discuss how they
divided their parents life.
2 Types of Change
—  Catastrophism: principle that states that all
geologic change occurs suddenly
—  Early Scientists beliefs – all things formed during a
rapid change
—  Ex. – Volcanic Eruptions
—  Uniformitarianism – the present is the key to the
past
—  James Hutton studied rock formation in Scotland
—  His findings led to the foundation of modern geology
Uniformitarianism
—  The process that we observe today, such as erosion
and deposition, does not change over time.
—  This idea states that the same geologic processes
that shape Earth today have been at work
throughout Earth’s history.
—  The average rate of geologic change is slow and has
remained relatively slow over time
Geologic Time Scale
—  Earth is 4.6 Billion Years Old
—  Scientists use the geologic time scale to make sense
of the amount of time.
—  Geologic Time Scale – divides the Earth’s history
into intervals of time defined by major events or
changes
But Why would we want to do that?
Geologic Time Scale
Geologic History
—  Eons (Largest Unit)
—  Hadean, Archean, Proterozoic, Phanerozoic
—  Precambrian – Hadean, Archean, Proterozoic
—  (90% of Earth’s History)
—  Eras
—  Phanerozoic (3 Era’s: Paleozoic, Mesozoic, Cenozoic)
—  Periods
—  Epochs - (Smallest Unit)
Fossil Record
—  5 divisions of geologic time
have ended in large mass
extinction events
—  Ex. – 250 Million Years ago
largest extinction ever known
(90% Marine and 70% Land)
—  Causes of Extinctions vary.
— 
— 
— 
— 
Movement of continents?
Lowering of global sea level
Rapid climate change
Asteroid impacts
Precambrian Time Outlined
—  Began with the formation of Earth
—  4.5 to 3.6 BYA Earth formed Oblate Spheroid
—  Tectonic Activity Began
—  Atmosphere was forming
—  Water vapor was added to atmosphere
—  Cyanobacteria began releasing Oxygen
—  Earth’s Land Surfaces were located near the poles
and covered in ice.
Paleozoic Era
—  Began 540 million Years Ago
—  Formation of Pangaea began
—  Sea Level Dropped
—  Pangaea drifted away from the South Pole
—  All life was in the Oceans
—  Era ended 250 MYA with Mass Extinction
Mesozoic Era
—  Began 250 MYA
—  Breakup of Pangaea
—  Mid Ocean Ridge Began to appear
—  Carbon Dioxide was added
—  Domination of Dinosaurs
—  65 MYA Mass Extinction
—  Thought to be caused by asteroid impact
Cenozoic Era
—  Began 65 MYA
—  Greenland Split apart from North America and
Europe
—  Final breakup of Pangaea
—  Continents assumed their present positions
—  Himalaya’s were formed
—  Temperature differences became extreme at poles
—  Evolution of Modern Humans
Exit Slip
—  One sentence Answer
—  What is the importance of the geologic time scale?