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

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

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

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

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

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

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

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

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

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

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 1 2 3 4 half lives of the 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 6.25 % 3.125 % 2 3 4 5 87.5% 93.75 % 96.875 % 1/2 1/4 1/8 1/16

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

5. What age are the following? a. 0.78125 % of the original 14C remains. b. 99.60938 % of the original 40K remains.

a. 0.78125 % of the original 14C remains. 50%  25%  12.5%  6.25%  3.125%  1 2 3 4 5 1.5625 %  0.78125 % 6 7 half lives 7 half lives [from the pattern on the chart] 7 half lives x 5730 years/ half life = 40,110 years

b. 99.60938 % of the original 40K remains. 50%  75%  87.5%  93.75%  96.875%  1 1/2 1/4 1/8 1/16 98.4375 %  99.21875 %  99.60938 % 1/32 1/64 1/128 half lives 1/128 half life x 1300 million years/ half life = 10.15615 million years

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