1. Deep Time

3. Radioistopes commonly used in Geological Dating
Radioisotope
Decay Mode
Decay reaction
Halflife
Use
14C (Atomic #6)
Carbon-14
(Beta) -decay
14C → 14N +e- + 
5730 yrs
Dating organic materials
26Al (Atomic #13)
Aluminum-26
26Al→ 26Mg +e- + 
720,000 yrs
Heating planetary interiors
40K (Atomic #19)
Potassium-40
40K→ 40Ca +e- + 
88% of orig 40K
1,251,000,000 yrs
Heating planetary interiors
(Electron) e--capture
40K+e- → 40Ar + 
12% of orig 40K
Dating igneous and metamorphic rocks
87Rb (Atomic #37)
Rubidium-87
87Rb→ 87Sr +e- + 
48,800,000,000 yrs
232Th (Atomic #90)
Thorium-232
(Alpha) -decay
232Th→ 228Ra +4He
(final prod =208Pb)
14,000,000,000 yrs
238U (Atomic #92)
Uranium-238
238U→ 234Th+4He
(final prod =206Pb)
4,468,000,000 yrs
235U (Atomic #92)
235U→ 231Th +4He
(final prod =207Pb)
704,000,000 yrs

4. U-238 Radioactive Family Daughters numbered in order of formation
Atomic #
Isotope #
Element
238
234
230
226
222
218
214
210
206 92
Uranium 1 4 91
Protactinium 3 90
Thorium 2 5 89
Actinium 88
Radium 6 87
Francium 86
Radon 7 85
Astatine 84
Polonium 8 11 14 83
Bismuth 10 13 82
Lead 9 12 15

5. U-238 Radioactive Family Half Lifes, Alpha in rows, Beta in columns
Atomic #
Isotope #
Element
238
234
230
226
222
218
214
210
206 92
Uranium
4,500,000
yrs
260,000 yrs 91
Protactinium
1.14 mins 90
Thorium
24.10 days
80,000 yrs 89
Actinium 88
Radium
1,620 yrs 87
Francium 86
Radon
3.82 days 85
Astatine 84
Polonium
3.05 mins
secs
138 days 83
Bismuth
19.7 mins
5 days 82
Lead
26.8 mins
22 yrs
stable