Chapter 4
Stratigraphy & Relative Age
Geologic History and Extinctions
Lesson 1 of 3
Quote Science of Today
• During his Zurich stay the woman doctor, Paulette
Brubacher, asked the whereabouts of his [Einstein's]
laboratory. With a smile he took a fountain pen out of
his breast pocket and said: 'here'. ~Albert Einstein~
• I chose this most brief quote by Albert Einstein because
it reminds me that the time to create is always HERE &
NOW! I think it is important to log down any insight or
idea no matter how slight it may seem. Even the
smallest sliver of information can make all the
difference when you put all the pieces together.
Old view of formation of Rocks
• 17th Century
• Catastrophism.- is the theory that the Earth has
been affected in the past by sudden, short-lived,
violent events
 Early Thoughts on the Origin Of Rocks
• Neptunism .- Rocks were created from water
having crystallized from earth’s First Oceans
• Plutonism.-
All rocks originated from Volcanoes pressure
and heat into Other Rocks
Stratigraphy
• Nicolas Steno 1638-1686 (Father of Modern Stratigraphy)
1. Principle of Original Horizontality
2. Principle of Superposition
3. Principle of Cross-Cutting Relationship
4. Principle of Lateral Continuity
5. Principle of Inclusions
6.- Principle of Faunal Succession
Principle of Original Horizontality
Principle of Original Horizontality
San Juan River, Utah
Canadian Rockies, Alberta
Principle of Superposition
Principle of Cross-Cutting Relationships
Igneous intrusion
Faulted rock
Principle of Inclusions
Principle of inclusions
Grand Canyon
Principle of Faunal (fossil) Succession
Index Fossils
 Def.: accurately indicate the ages of sedimentary rocks
1) Abundantly preserved in rocks
2) Geographically widespread
3) Fast evolving - existed for a relatively short time
4) Easily identified
James Hutton ( Modern Geology)
Siccar Point @ Scotland
Siccar Point
UNIFORMITARIANISM
• UNIFORMI…… What ?
• “The Present is the Key to the Past “
• Rate and intensity of past process were they
same as those observed today.
• This principle is still the foundation of geologic
science
UNIFORMITARIANISM
Current understanding of Uniformitarianism in
geology is no longer makes this assumption
 Rates and intensity of process
( Different conditions on earth trough time)
Catastrophes do play a role
( Chicxulub, Massive volcanic Flows)
UNCONFORMITIES
Breaks in the rock record. (time missing in the Geologic
record)
a) Angular Unconformities.- When Rocks are tilted at angle by
uplifting, faulting or folding
b) Disconformity .- Is difficult to see because both layers are
sedimentary rocks and both are still horizontal but they are separated by
the surface that got eroded.
c)Nonconformity .- Is abreak in time between a metamorphic or
intrusive igneous rock and layers of Sedimentary rocks created above it.
Angular Unconformity
Disconformity
Nonconformity
Unconformities
• Unconformities
• Geologic Time Record
Chapter 4
• Absolute Age
• Geologic History and Extinctions
• Lesson 2 of 3
Science Quote
"Anybody who has been seriously engaged in
scientific work of any kind realizes that over that
same entrance to the gates of the temple of
science are written the words: 'Ye must have
faith'"
Max Planck
• Anacany Ramirez
Review Stratigraphy
Conformable Principles
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Unconformities
Principle of Original Horizontality a) Angular Unconformities.b) Disconformity .Principle of Superposition
c)Nonconformity
Principle of Lateral Continuity
Principle of Cross-Cutting
Time missing from the rock layers. Breaks
Relationship
in the rock record
Principle of Inclusions
Principle of Fossil Succession
Assumption that the rocks you examine
have undisturbed and complete record
Relative Dating: Correlation
How old is that rock?
 Relative age: order of events
Relative dating tells us what order things happened,
but not how many years ago they happened.
 Absolute age: age in years
Absolute Dating: Radioactive Decay
Half Life
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1 gram of K-40 (Potassium 40 )
(Half Life 1.3 Billion Years)
.50 gram
Half Life 1.3 Billion Years)
.25
Another Half-life Example
• You start with $1000 in your bank account
• Every week your spouse or boyfriend/girlfriend
removes half of the money
• The half-life of your account = 1 week
1 week
Your Bank Account
(1 half-life)
•
•
•
•
•
•
•
•
•
•
Start: $1000
Week 1: $500
Week 2: $250
Week 3: $125
Week 4: $62.50
Week 5: $31.25
Week 6: $15.63
Week 7: $7.81
Week 8: $3.90
Week 9: $1.95
•
•
•
•
•
•
•
Week 10: $0.98
Week 11: $0.49
Week 12: $0.24
Week 13: $0.12
Week 14: $0.06
Week 15: $0.03
Week: 16: $0.015 left in
your bank account
Isotopes & Half Lives
Young things
Old things
Radiometric Dating
Is the process of determining the absolute age of rocks, minerals and fossils by
measuring the relative amounts of parent and daughter isotopes
Radioactive Decay Curve
Calculating Absolute Age
• Potassium-40 included in mineral (start clock)
• Begins decaying to Argon-40
• Brilliant scientists have told us the half-life of K-Ar is
1.3 billion yrs (Gyr)
• We count # parents & daughters in sample
• We find that our sample contains 50% K & 50% Ar
• So 1/2 of our initial sample (K) has decayed
• How old is it?
• We find another sample that is 25% K & 75% Ar
• How old is it?
Continue with chapter 4
• Class 3 of 3
“I don’t drink water, because if water can erode rock, think what it can do to
flesh. ”
― Jarod Kintz,
Amanda Barraza
Earth Rocks, Earth History,
and Mass Extinctions
• The fossil record suggest that sudden,
catastrophic events, abruptly decimated Life
on earth.
• But, New life forms emerged following mass
extinctions
Mass Extinctions
Hypothesis for mass extinctions
• Extraterrestrial Impacts
• Volcanic Eruptions
• Supercontinents
Systems interactions among Biosphere, Geosphere,
Atmosphere. Hydrosphere
EXAMPLE:
Permian Extinction: 90 % of all species in oceans died
70% of reptiles and amphibians
30% of all insects
A Bad Day…. 65 Million Years Ago
Chicxulub crater gravity anomaly
Mass Extinctions:
Extraterrestrial Impacts
Astronomical Impacts
1.
LARGE OBJECT HITS EARTH.- the impact sends large amounts of rock and
other debris in to Atmosphere and it starts fires, which add some and ash to
the Atmosphere
2.- The Atmosphere is polluted. Particles of ash and rock in the atmosphere do 3
Things :
• Block sun light
• Block sun warmth, leading to global cooling
• Create conditions for acid rain.
Also This darkened atmosphere may also be very difficult to breath in
3. Plant Life gets affected. The combination of acid rain, cooler temperatures, and
the absence of sunlight SHUTS DOWN the process of Photosynthesis.
Brings Plant Life TO A HALT
4.- Hervibores are affected next. Without plants  no food.
5 The Entire ecosystem collapses
Mass Extinctions: Volcanic Eruptions
The Siberian trap basalts formed 250
million years ago at the Permian/Triassic
boundary with a volume of 2.5 million cubic
kilometers
Fig. 4-2, p.75
Example Eruptions:
Global distribution of large igneous provinces in the oceans (submarine
plateaus) and on land (flood basalts)
Mass Extinctions:
Atmosphere-Ocean-Continent Interactions
Ocean Conveyor
Mass Extinctions:
Atmosphere-Ocean Interaction (1)
Fig. 4-2, p.75
Mass Extinctions:
Atmosphere-Ocean Interaction (2)
Mass Extinctions:
Atmosphere-Ocean-Continent Interactions
Mass Extinctions:
Ocean-Continent Interaction
Pangea
Geologic time (millions of years)
Geologic Time & Biology
Geologic time (millions of years)
Geologic Time & Biology
Fig. 4-1b, p.74
Geologic time (millions of years)
Geologic Time & Biology
Geologic Time
 Major divisions
 Cenozoic: 66 - 2.5 m.y.a
 Mesozoic: 245 - 66 m.y.a.
 Paleozoic: 544 - 245 m.y.a.
 Precambrian: pre-544 m.y.a.
(proterozoic)
Geologic Time
Earth History in One Year