70 likes | 178 Vues
Discover the age of Earth using radioactivity measurements from decay series like Potassium-40 & Uranium-238. Learn about isotopic abundance and decay constants in this fascinating study of Earth's geological history.
E N D
Radioactivity in the Earth’s Crust • One can find the age of a rock by measuring the amount of radioactivity • In particular one is interested in the daughter decay series • K40 half life (T1/2 1277 million years) • Isotopic Abundance 0.118 % • Age of earth about 4 billion years
Second Method Uranium and Actinium decay series • U238 T1/2 = 4468 million years • U235 T1/2 = 703.8 million years • Both of these isotopes are not made in stars. They are “Transuranic Elements” • Probably made during big bang and in Supernovae explosions • Assume original abundance of these two isotopes were the same
Radioactive Decay • Radioactive Decay is a logarithmic decay • N is the number of atoms after a time t • N0 is the original number of atoms at time 0 • is the decay constant t is the elapsed time = lne2 /T1/2 = 1/(1.44 T1/2) (Can be either years or seconds)