Area
of Focus: Geologic Time.
Copyright © 2010 Ryan P. Murphy
Human existence - The
last few seconds of the
last minute before
midnight.
“I am only a few
thousand years
old.” “Incredibly
young in earth’s
very long history.”
Uniformitarianism : The laws of nature have not
changed over time.
Copyright © 2010 Ryan P. Murphy
•Laws of nature:
–How chemicals react?
–How water erodes materials?
–Laws of physics?
•These are things that don’t change. They occur today as
they did Billions of years ago.
Principle
of superposition: Oldest rocks and
fossils are on bottom, youngest on top.
Youngest Rock Layers
Oldest Rock Layers
Human remains are only found
at the very top of the fossil
record. We are a young species.
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon, Archeon
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon, Archeon, Proterozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon, Archeon, Proterozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon, Archeon, Proterozoic, Phanerozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Eon (Longest amount of time)
–Hadeon, Archeon, Proterozoic, Phanerozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Era (Second longest unit of time)
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Era (Second longest unit of time)
–Paleozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Era (Second longest unit of time)
–Paleozoic, Mesozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Era (Second longest unit of time)
–Paleozoic, Mesozoic, Cenozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Era (Second longest unit of time)
–Paleozoic, Mesozoic, Cenozoic
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Period (Third longest unit of time)
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Period (Third longest unit of time)
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Epoch (Shortest Unit of Geologic Time)
Copyright © 2010 Ryan P. Murphy
•Earth’s Timeline is divided into various units of time.
–Epoch (Shortest Unit of Geologic Time)
–Cenozoic Era
Copyright © 2010 Ryan P. Murphy
The
system is fragile. Changes in living conditions
for animals have been numerous throughout Earth’s
history.
Copyright © 2010 Ryan P. Murphy
•Are you ready for the fact on the next slide.
It is a fact that is very scary.
•99.5% of all things that have ever lived have
become extinct.
Copyright © 2010 Ryan P. Murphy
Mass
Extinctions
• Please use this
handout to take
notes on the
different time
periods in
geologic history.
• There will be Red
slides as usual.
• We will be
starting near the
bottom.
This black space
represents the
Precambrian period of
Earth’s History 87%
his black space represents the other 13% of
ime. From the first multi-cellular life to now.
13%
87%
Precambrian Super Eon

Precambrian
 Formation
of Earth
 Earliest rocks, single
celled life, first
multi-celled life
 Extinction of
anaerobes (nonoxygen breathers)
Paleozoic Eon
Cambrian
Explosion
Millions of
Years
Most massive extinction event the
planet had ever seen. Environmental
change, impact event, volcanism, and
sea floor methane release.
“99.5%”

Paleozoic
 Ocean
plants
 Cambrian Explosion
(many different
species arise)
 Trilobites, Land plants
 Age of: Invertebrates
Fish  Amphibians
 Permian Extinction:
83% of life died
Mesozoic Era
“99.5%”

Mesozoic
 Age
of Reptiles
(Dinosaurs)
 First mammals, birds
and flowers
 Cretaceous-Tertiary
Extinction, 50% of life
died, including dinosaurs
Cenozoic Eon

Cenozoic
 Age
of Mammals
 First hominids (Apes
ancestors of humans)
 First Homo Sapiens
(Humans)
How Do We Know?
Two types of dating:

Two types of dating:


Relative dating – tells us the order in
which events occurred (no dates)
-

Relative dating – tells us the order in which
events occurred (no dates)
-
-

Relative dating – tells us the order in which
events occurred (no dates)
 ??????
-
-
(we already know one)

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
-
-

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
 Cross-Cutting:
Intrusions and faults in rocks
are younger than the rocks they cut across
-

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
 Cross-Cutting:
Intrusions and faults in rocks
are younger than the rocks they cut across
– evidence of past life found in
sedimentary rocks
 Fossils
-

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
 Cross-Cutting:
Intrusions and faults in rocks
are younger than the rocks they cut across
– evidence of past life found in
sedimentary rocks
 Fossils
 Cast/Mold
Cast/Mold
Are these
bones?

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
 Cross-Cutting:
Intrusions and faults in rocks
are younger than the rocks they cut across
– evidence of past life found in
sedimentary rocks
 Fossils
 Cast/Mold
 Impression
Impression

Relative dating – tells us the order in which
events occurred (no dates)
 Superposition
 Cross-Cutting:
Intrusions and faults in rocks
are younger than the rocks they cut across
– evidence of past life found in
sedimentary rocks
 Fossils
 Cast/Mold
 Impression
 Remains
Remains
Two types of dating:
Relative
 Absolute – Actual date

-
Two types of dating:
Relative
 Absolute – Actual date

 Radioactive
Decay/Radiometric dating –
Uranium loses subatomic particles at a
constant rate. We can tell how old a
rock is by how much the uranium has
decayed.
Two types of dating:
Relative
 Absolute – Actual date

 Radioactive
Decay/Radiometric dating –
Uranium loses subatomic particles at a
constant rate. We can tell how old a
rock is by how much the uranium has
decayed.
 Index Fossil – Lived for a short period of
time but covers a large area of Earth.
(Trilobite)
Trilobites
only lived
from 570 mya
to 500 mya.
So the layers of
sediment they are
found in were laid
down during that
time.
This snail can
be dated
because we
know it was
laid down at
the same
time as the
trilobite.