1. Learning Objective:
I will be able to explain how we use fossils to date rocks.

2. Success Criteria: I can explain how fossils help us to date rocks.
I can explain how index fossils differ from fossils.
I can identify fossils on the ESRT and use them to date rocks.

3. Correlation
Matching similar rock layers in different locations to see if they formed at the same time

4. f03_09_pg37
f03_09_pg37.jpg

5. 1. Which layers are the same?
2. Which layer is older E or F?
3. What is correct sequence of rock layers from oldest to youngest?
4. An unconformity is represented by the interface between which 2 layers?

6. February 19
Fossils
Naturally occurring preserved remains or impressions of living things
Generally only hard parts get preserved
Bones, teeth, shells
Hard parts are replaced by naturally occurring minerals
Allen

7. Eurypterus
NY State Fossil
Silurian index
fossil

8. Which fossil might be found in Devonian rock layers?

9. Fossils Why don’t fossils exist in most igneous or metamorphic rock?
February 19
Fossils
Generally found in sedimentary rock layers
Why don’t fossils exist in most igneous or metamorphic rock?
Allen

10. February 19
Fossils
The living organism that made the fossil lived during the time the rock layer was forming
i.e. when the sediment was being deposited
Allen

11. Fossils Fossils can provide information about ancient environments
Marine fossils=marine environment,
wooly mammoths= cold environment, etc…

12. Fossils A study of the fossil record shows:
February 19
Fossils
A study of the fossil record shows:
A great variety of plants, animals and simpler life forms have lived on Earth in the past
Life forms have evolved through time
Most life forms have become extinct
Allen

13. Index Fossils Index Fossils--used to date rock layers (strata)
Fossils from creatures that existed for a geologically short period of time
Ex. less than 2.0 x 107
Fossils from creatures that had a wide geographic distribution

14. Which letter would make a good index fossil?
Location A
Location B
Location C
Rock layer 1 W
W Z
Rock layer 2
W Z Y Z
Rock layer 3
W X X
X Z
Which letter would make a good index fossil?

15. Volcanic Ash Falls
Can also be used to correlate rock layers over a large area
Ash is a good indicator because:
The ash from one explosion has distinct characteristics
ash can be deposited around the globe
The event occurs at one, geologically brief, time

16. Summary: Success Criteria Recap
I can explain how fossils help us to date rocks.
I can explain how index fossils differ from fossils.
I can identify fossils on the ESRT and use them to date rocks.

17. Absolute Dating

18. When an unstable radioactive element changes into a stable element
Radioactive Decay
When an unstable radioactive element changes into a stable element

19. Example Unstable Radioactive Isotope Stable Decay Product
Carbon 14 (C14)
Nitrogen 14 (N14)
Uranium 238 (U238)
Lead 206 (Pb206)
Parent
Daughter

20. Radiometric Dating
Half life: The time required for 1/2 of a parent material to break down to daughter material

21. Another look

22. Radiometric Dating
The age of objects can be determined by measuring the relative amounts of radioisotope and decay products

23. Radiometric Dating
The half lives of radioisotopes vary depending upon the isotope
Examples:
C14 = 5,770 years
U238 = 4,500,000,000 years
Rb87 = 47,000,000,000 years

24. Carbon 14 is used to date biological remains
Carbon is incorporated into the cells of living organisms and begins to decay when the organism dies
Uranium 238 is used to date rocks
Larger half life

25. Half Life Practice Problems

26. If half the K -40 of a rock has decayed into Ar-40, how old is the rock?
How many years would it take for 75 % of a sample of K-40 to disintegrate?

27. A sample that has ½ c-14 and ½ n-14?
How old are:
A sample that has ½ c-14 and ½ n-14?
A sample that has ¼ K-40 and ¾ Ar-40?
A sample that has ½ U-238 ½ Pb-206?

28. How old are:
A sample that has 1/8 Rb-87 and 7/8 Sr-87?
A sample that has ¼ C-14 and ¾ N-14?
A sample that has ¾ C-14 and ¼ N-14?

29. What fraction remains of:
February 19
A 50 billion year old sample has ____ Rb-87 and ____ Sr-87.
A 2.6 billion year old sample has____ K-40 and ____Ar-40.
Allen

30. Stranz should take a break ;)
This is so boring
Stranz should take a break ;)