Absolute Ages of Rocks

Sci. 3.3

Absolute age:• Age in years

Question 1

Nucleus (center) of atom:• Protons, + charge

• Neutrons, No charge (Neutral)

• Electrons, - charge outside nucleus

P

e-

H

PN

NP

e-

e-

He

PN

NP

e-

e-

PN

e-

Li

Draw these

Question 2

2a. Which subatomic particle is not found in the nucleus? P. n. e2b. A neutron has a _____ charge. Positive, negative, no charge

Number of protons:• Determines identity of element

Pe-

H

PN

NP

e-

e-

He

PN

NP

e-

e-

PN

e-

Li1 23

P PP

Question 3

3a. If a He atom lost a proton, it would become what element? H, Li, C, O

3b. If a He atom gained a proton, it would become what kind of atom? H, Li, C, O

Number of neutrons:• Determines which form (isotope) of element

6 P6 N

6 P8 N

Carbon Carbon

7 P7 N

Nitrogen

12C 14C

14N

12 14

14

19 P21 N

11 P12 N

Potassium Sodium

18 P22 N

Argon

40K 23Na

40Ar

40 23

40

Hydrogen Nitrogen

Phosphorus

2H 15N

28P

2 15

28

1 P1 P1 N

7 P7 P8 N

15 P15 P13 N

Question 4

4a. How many neutrons does the isotope 14C have? 6, 7, 8, 14

4b. How many neutrons does the isotope 13C have? 6, 7, 8, 13

Some isotopes are unstable• Radioactive decay

Parent material Daughter material 14C 14N e-

Question 5

5a. All carbon atoms have __ protons. 6, 7, 8, 145b. All nitrogen atoms have __ protons. 6, 7, 8, 14

Half-life:• Time it takes for half of atoms to decay

• Ex:14C = 5730 years (235U=700 m.y., 238U=4.5 b.y.)

Question 6

6a. If an organism had 100g of 14C when it died around 11,500 years ago (2 half-lives), how much 14C would it have today? 200, 50, 25g, 15g

6b. If an organism had 120g of 14C when it died around 17,000 years ago (3 half-lives), how much 14C would it have today? 360, 60, 30g, 15g

Radiometric dating:• Calculating age based on half-life

• ratio of parent material to daughter material

Question 7

Radiocarbon dating:

• For dating dead things

• good to 75k years ago

• For original remains only

• (dinos 65mil )

Shroud of Turin

Question 8

8a. Would radiocarbon dating be useful for dating the exact age of the earth (~4.6 billion years)? Y/N8b. Would radiocarbon dating be useful for dating a trace fossil that is around 50k years old? Y/N

Earth’s age• ~4.5 bil. years

• Oldest rocks ~3.9 bil

Question 9

9a. The earth is approximately how old? 4.5 bil, 4.5 mil, 4.5 thousand9b. When the earth first formed, its surface: was molten rock, lacked liquid water, did not have an atmosphere, all of the above

uniformitarianism:• Processes that change the earth today, are the same

that changed it in the past

Question 10

10a. The processes that shape the earth’s surface generally work: very slowly, very quickly10b. Which process forms new elements? uniformitarianism, superposition, permineralization, radioactive decay