Earth Sciences 1022A/B Lecture Notes - Lecture 8: Half-Life, Decay Product, Mesozoic

• School: Western University
• Department: Earth Sciences
• Course: Earth Sciences 1022A/B
• Professor: Molnar

Document Summary

Rates of decay are commonly expressed in terms of half-life. Half-life is the time required for half of the parent atoms in a sample to decay to daughter atoms. Half-life of potassium-40 is about 1. 25 billion years. This means that for a sample consisting of both parent and daughter isotopes . If sample consists of 1/2 parent (remaining) and 1/2 daughter (produced), 1 half life has passed. 1/4 parent (remaining) and 3/4 daughter (produced), 2 half lives has passed. 1/8 parent (remaining) and 7/8 daughter (produced), 3 half lives have passed. 1/16 parent (remaining) and 15/16 daughter (produced), 4 half lives have passed. Each half-life represents the halving of the preceding amount of parent isotope. A sample containing 1/4 parent (k-40) isotope and 3/4 daughter isotope (ar-40) means that 2 half lives have elapsed (because x = ). So, 2 half-lives x 1. 25 billion years (half life for k-40) = 2. 5 billion years.