Class 4: Stratigraphy & Class 4: Stratigraphy & Age Dating Age Dating Geologic History and Geologic History and Extinctions Extinctions y’s topics: haracterizing geologic time elative ages (stratigraphy) bsolute ages (radioactive decay) Today’s topics: Earth History Mass Extinctions Geologic Time Scale
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Class 4: Stratigraphy & Age Dating Geologic History and Extinctions Today’s topics: Characterizing geologic time Relative ages (stratigraphy) Absolute.
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Class 4: Stratigraphy & Age Class 4: Stratigraphy & Age DatingDating
Geologic History and Geologic History and ExtinctionsExtinctions
Class 4: Stratigraphy & Age Class 4: Stratigraphy & Age DatingDating
Geologic History and Geologic History and ExtinctionsExtinctions
Class updates: Reading: Section 4.0-4.6 Homework 1 due today Homework 2 online, due next Mon. Midterm practice online (website) Midterm review online (website) Midterm 1 on Feb. 28th (next Mon.)
How old is that rock?
Determining Relative Geologic Time
1. Principle of Original Horizontality2. Principle of Superposition3. Principle of Cross-Cutting
Relationship4. Principle of Faunal Succession
Principle of Original Horizontality
Principle of Original Horizontality
San Juan River, UtahSan Juan River, Utah Canadian Rockies, AlbertaCanadian Rockies, Alberta
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?
Mass Extinctions
A Bad Day…. 65 Million Years Ago
Mass Extinctions:Extraterrestrial Impacts
Fig. 4-2, p.75
Mass Extinctions:Volcanic Eruptions
Fig. 4-2, p.75
Example Eruptions:
Mass Extinctions:Atmosphere-Ocean-Continent Interactions
Evolution of Earth Atmosphere
Nitrogen
Oxygen
All Others
Fig. 4-2, p.75
Mass Extinctions:Atmosphere-Ocean Interaction (1)
Mass Extinctions:Atmosphere-Ocean Interaction (2)
Mass Extinctions:Atmosphere-Ocean-Continent Interactions