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

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

III. DATING FOSSILS 3. this works by sediments being deposited over time by erosion 2. the system depends on the rule that older things are buried deeper 1. few fossils can be dated directly

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

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

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

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

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

1. we know that A is younger than volcanic ash # 1 A B C D E 5. we assume that B and E are the same age by distance above volcanic ash # 2 4.we assume that C is younger than B and E because it is shallower 3.we know that D is older than volcanic ash # 2 2. we know that B, C and E are older than volcanic ash # 1 and younger than volcanic ash # 2

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

¼ ½ half lives of the isotope %PARENTALISOTOPE%PARENTALISOTOPE 87.5 % PARENTAL ISOTOPE 12.5 % DAUGHTER ISOPTOPE 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 % DAUGHTER ISOTOPE

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

Parental isotope remaining Half lives 50 % 25 % 75 % 12.5% / % 1/ % % 1/ % % 1/16

4. Examples of commonly used isotopes 14 C 14 N – 100, K 40 Ar1.3 billion 100,000 – 4.6 billion 235 U 207 Pb713 million 10 million – 4.6 billion parental isotope daughter isotope half life in years range (yrs)best for biotic ash rock

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

a % of the original 14 C remains. 7 half lives [from the pattern on the chart] 50%  25%  12.5%  6.25%  3.125%  %  % 6 7 half lives 7 half lives x 5730 years/ half life = 40,110 years

b % of the original 40 K remains. 50%  75%  87.5%  93.75%  %  1 1/2 1/4 1/8 1/ %  %  % 1/32 1/64 1/128 half lives 1/128 half life x 1300 million years/ half life = million years

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