1. WHEN ? WHAT ? WHY ? 65 million years ago
a giant meteorite crashing into the earth, severely disrupting the earth's ecosystem
85% of all species including all of the dinosaurs, many fish, plankton and many plants either died out completely or suffered heavy losses
65 million years ago
or volcanic activity, climate change, environmental pollution

2. WHEN ? WHAT ? WHY ? Next? Human induced climate change
50% of species including all plants and animals
Human induced climate change

3. III. DATING FOSSILS 1. few fossils can be dated directly
the system depends on the rule that older things are buried deeper
3. this works by sediments being deposited over time by erosion

4. a. creature dies near site of erosion and parts do not decompose

5. b. Dead creature is buried & other creatures die in same area

6. over time, remains of newer dead creatures are buried
above older remains

7. What can be dated? no Dirt – seldom Fossils – Volcanic ash –
yes! Using K / Ar

8. Example of dating fossils
SOIL SURFACE A
VOLCANIC ASH # 1 C B
VOLCANIC ASH OR LAVA # 2 E D

9. 1. we know that A is younger than volcanic ash # 1
2. we know that B, C and E are older than volcanic ash # 1 and younger than volcanic ash # 2 C B
we know that D is older than
volcanic ash # 2 E
we assume that C is younger than B
and E because it is shallower D
5. we assume that B and E are the same age by distance above volcanic ash # 2

10. C. RADIOMETRIC DATING
1. Radio-isotopes atoms that decay with a set half life
2. half life --- time required for ½ of the parental isotope to decay to a daughter isotope

11. half lives of the isotope
87.5 % PARENTAL ISOTOPE
12.5 % DAUGHTER ISOPTOPE % P A R E N T L I S O 75 50 25
12.5
75 % PARENTAL ISOTOPE
25 % DAUGHTER ISOTOPE
50 % PARENTAL ISOTOPE
50 % DAUGHTER ISOTOPE
25 % PARENTAL ISOTOPE
75 % DAUGHTER ISOTOPE
12.5 % PARENTAL ISOTOPE
87.5 % DAUGHTER ISOTOPE
6.25 % PARENTAL ISOTOPE
93.75 % DAUGHTER ISOTOPE
¼ ½
half lives of the isotope

12. 3. given the half life and the relative amounts of the elements,
the age of the item can be determined using an equation
4. however, an approximation can be done with no more math than the ability to divide by 2
and subtract from 100

13. Parental isotope remaining
Half lives
50 %
25 %
75 %
12.5% 1
6.25 %
3.125 % 2 3 4 5
87.5%
93.75 % %
1/2
1/4
1/8
1/16

14. 4. Examples of commonly used isotopes
parental isotope
daughter isotope
half life in years
range (yrs)
best for
100 – 100,000
14C
14N
biotic
5730
100,000 – 4.6 billion
40K
ash
40Ar
1.3 billion
10 million – 4.6 billion
235U
207Pb
713 million
rock

15. 5. What age are the following?
a % of the original 14C remains.
b % of the original 40K remains.

16. a. 0.78125 % of the original 14C remains.
50%  25%  %  %  % 
%  %
half lives
7 half lives [from the pattern on the chart]
7 half lives x 5730 years/ half life = 40,110 years

17. b. 99.60938 % of the original 40K remains.
50%  75%  %  %  % 
/ / / /16
%  %  %
1/ / /128 half lives
1/128 half life x 1300 million years/ half life
= million years

18. Work on assignment sheet