1. Relative and Absolute Dating

2. Relative dating - the age of a rock, fossil, or other feature measured
Relative dating the age of a rock, fossil, or other feature measured compared to another.

3. Absolute dating - (numerical dating) the age of a rock in years.

4. Relative Dating Laws:

5. #1 Original Horizontality Sedimentary rocks are formed in layers which were originally horizontal

6. Observe flat layers - rocks undisturbed Observe tilted layers - tectonics at work

7. #2 Lateral Continuity The horizontal layers continue in all directions at the time that they form

8. Lateral Continuity image

9. #3 Superposition Oldest rocks are on the bottom, Youngest rocks are on the top

10. Superposition image
Younger

11. #4 Cross-cutting relationships Igneous intrusions and faults are younger than the sedimentary rocks that they cut across

12. Cross-cutting relationships image

13. Unconformities
Represent intervals of time when layers are missing from the geologic record
Caused by Uplift and Erosion

14. Grand Canyon Example
Grand Canyon Example

15. Principles of Fossil Succession
Fossil organisms succeed one another in a definite order
Any time period can be recognized by its fossil content
Examples: age of humans, ages of fishes, age of dinosaurs, etc.
This is application of the
Principle of Superposition
Important for Correlation

16. Index Fossils
Fossils useful as time indicators
Short age range
Easily recognized
Widespread distribution

17. Index Fossils image

18. For that, we need Absolute dating
Relative dating tells us what order things happened, but not how many years ago they happened
For that, we need Absolute dating

19. Absolute dating:

20. Radiometric Dating Process used to determine the absolute age of a rock or a fossil by determining the ratio of parent nuclei to daughter nuclei within a given sample.

21. Radioactive atoms are like clocks All minerals contain some radioactive atoms Only works for IGNEOUS rocks

22. Procedures that count the products of radioactivity to date rocks
Radiometric Dating
Procedures that count the products of radioactivity to date rocks

23. When atomic nuclei spontaneously break apart Types: Alpha emission
Radioactivity
When atomic nuclei spontaneously break apart
Types:
Alpha emission
Beta emission
Gamma rays

24. Alpha Emission

25. Beta Emission

26. Radiometric dating keys:
Knowing the HALF LIFE
Having the parent and the daughter together in your mineral

27. Half-life Example #1 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
Questions to think about:
When is the most money taken out?
Will the amount in your bank account ever go to zero?

28. Your Bank Account Start: $1000 Week 1: $500 Week 2: $250 Week 3: $125
Week: 16: One and a half cents left in your bank account

29. Radioactive Decay Curve image

30. Radiometric Dating Limitations
Sedimentary Rocks
Weathered material of other rocks
Radiometric clock has been altered
Metamorphic Rocks
Radiometric clock has been altered?
Igneous Rocks
Minerals form when rock forms
No Problem – best source for radiometric dating

31. Radiometric Decay Data Front Page of ESRT’s

32. Carbon 14 Only useful in finding the age of ORGANIC materials up to 75,000 years old.

33. Carbon 14 Decay Curve

34. Other types of Absolute Dating

35. Tree Rings
Annual growth rings are a function of their environment, i.e. temperature, humidity, precipitation, insects, fires, etc.
Limited to recent geologic past (furthest back 8000 years)

36. Ice Layers
Ice Sheets in Greenland and Antarctica record annual changes in accumulation and snowmelt
Records up to 65,000 years
Ice also traps volcanic ash which can be radiometrically dated
Record climatic conditions of the Earth

37. Ash Layers
Ash Layers from major volcanic eruptions create KEY BEDS – a distinct layers of known age

38. Geologic Time Scale
Eon/Era/Period names - based on fossil assemblages, superposition
Absolute ages, from radiometric dating