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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
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