7.2 Half Life Half Life: the constant rate at which radioactive isotopes naturally decay. This rate refers to the time it takes for half of the nuclei of a sample to decay. With every half life, half of the remaining nuclei decays until there is no more.

Carbon Dating (C-14) Carbon has 3 isotopes: C-12, C-13 and C-14 All organisms contain carbon. When an organism is alive the ratio of C-12 to C-14 is equal…but when an organism dies C-12 remains constant but C-14 decays without being replaced. Overtime the ratio of C-14 and C-12 decreases This ratio is used to estimate the age of an organisms remains. Radiocarbon dating: process that determines the age of an organism by determining the C-14 remaining. Only organisms that have lived within the last 50,000 yrs

Carbon Dating

Decay Curves A curved line on a graph that shows the rate at which radioisotopes decay Regardless of the radioisotope graphed all decay curves have a similar shape Difference: half life length will vary, every isotope has its own half life which can range from 1 second to an hour to thousands of years etc.

Decay Curve

Potassium-40 Clock Parent Isotope: the isotope that undergoes radioactive decay Daughter Isotope: the stable product of the radioactive decay. Isotope pairs can be used in radioactive dating. Notice how the dating ranges differ based on half-life. See Table 7.6 on pg 307 Notice how the red and blue curves intersect at the 1st f half life only 