Page 243 - Laboratory Manual in Physical Geology

SOME ISOTOPES USED FOR RADIOMETRIC DATING
Parent Daughter Half-Lives (T ) Materials Dated Useful Dating Range
1
Newly formed Isotope (P) Isotope (D) /2
crystal
Uranium-238 Lead-206 4.5 billion years Zircon ages > 10 m.y.
100
Uranium-235 Lead-207 713 million years Zircon ages > 10 m.y.
Potassium-40 Argon-40 1.3 billion years Biotite, muscovite, ages > 50,000 yr
15.9% whole volcanic rock
decayed to
daughter Carbon-14 Nitrogen-14 5730 years Shells, limestone, ages 100–60,000 yr
84.1 29.3% organic materials
Percent of Parent (P) Atoms Remaining 50.0 decayed 50% RADIOACTIVE Parent
70.7

Atoms (P)

DECAY
decayed
Daughter
Atoms (D)

25.0
75% decayed
87.5%
12.5 decayed
93.8%
decayed 96.9%
6.2 decayed
3.1
0
0 1 / 4 1 / 2 1 2 3 4 5 6
Half-Lives (T ) Elapsed
1
/2

DECAY PARAMETERS FOR ALL RADIOACTIVE DECAY PAIRS
Percent of Percent of Half-Lives
Parent Daughter Age
Atoms (P) Atoms (D) Elapsed
100.0 0.0 0 0.000 x T1
/ 2
98.9 1.1 1/64 0.015 x T1
/ 2
97.9 2.1 1/32 0.031 x T1
/ 2
95.8 4.2 1/16 0.062 x T1
/ 2
91.7 8.3 1/8 0.125 x T1
/ 2
84.1 15.9 1/4 0.250 x T1
/ 2
70.7 29.3 1/2 0.500 x T1 2 /
50.0 50.0 1 1.000 x T1
/ 2
1
35.4 64.6 1 / 2 1.500 x T1 2 /
25.0 75.0 2 2.000 x T1
/ 2
12.5 87.5 3 3.000 x T1 2 /
6.2 93.8 4 4.000 x T1
/ 2
3.1 96.9 5 5.000 x T 1
/ 2

FIGURE 8.11 Radiometric dating. Some isotopes useful for radiometric dating, their decay parameters, and their useful ranges

for dating. The half-life of each decay pair is different (top chart), but the graph and decay parameters (bottom charts) are the same for all
decay pairs.
Dating of Rocks, Fossils, and Geologic Events ■ 215