Chapter 4

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 Horizontality2. Principle of Superposition3. Principle of Cross-Cutting Relationship4. Principle of Lateral Continuity5. Principle of Inclusions6.- 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

Faulted rockIgneous intrusion

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 rocks2) Geographically widespread3) Fast evolving - existed for a relatively short time4) Easily identified

Siccar Point @ Scotland

James Hutton ( Modern Geology)

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

UNIFORMITARIANISMCurrent 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 • Principle of Original Horizontality• Principle of Superposition• Principle of Lateral Continuity• Principle of Cross-Cutting

Relationship• Principle of Inclusions• Principle of Fossil Succession

Unconformitiesa) Angular Unconformities.-b) Disconformity .- c)Nonconformity

Time missing from the rock layers. Breaks in the rock record

Assumption that the rocks you examine have undisturbed and complete record

Relative Dating: Correlation

How old is that rock?

Relative age: order of events

Absolute age: age in years

Relative dating tells us what order things happened, but not how many years ago they happened.

Absolute Dating: Radioactive Decay

Half Life

• 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

• 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

(1 half-life)

Isotopes & Half Lives

Young things

Old things

Radiometric DatingIs 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

EXAMPLE:Permian Extinction: 90 % of all species in oceans died

70% of reptiles and amphibians 30% of all insects

Systems interactions among Biosphere, Geosphere, Atmosphere. Hydrosphere

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

Fig. 4-2, p.75

Mass Extinctions: Volcanic EruptionsThe Siberian trap basalts formed 250 million years ago at the Permian/Triassic boundary with a volume of 2.5 million cubic kilometers

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

Fig. 4-2, p.75

Mass Extinctions:Atmosphere-Ocean Interaction (1)

Mass Extinctions:Atmosphere-Ocean Interaction (2)

Mass Extinctions:Atmosphere-Ocean-Continent Interactions

Mass Extinctions:Ocean-Continent Interaction

Pangea

Geologic Time & BiologyGe

olog

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me

(mill

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Fig. 4-1b, p.74

Geologic Time & BiologyGe

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(mill

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Geologic Time & BiologyGe

olog

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(mill

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of y

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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