Deep Time
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
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
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 .000150 secs 138 days 83 Bismuth 19.7 mins 5 days 82 Lead 26.8 mins 22 yrs stable