24Absolute AgeRadioactive decay = the decay of unstable isotopes (parent) into stable elements (daughter).Isotope = element has different masses (or amount of neutrons).Ex. Uranium 238 (radioactive) decays into Lead 206 (stable).
25Why use radioactivity? Decay rate is predictable. Immune to external forces: heat, pressure, chemical, and mass.Decay begins:rocks: when formed.organic: when life ends.
26Half-Lifetime it takes for half or 50% of the parent to decay into the daughter.
27LimitationsAir, Water, Life: C14 / C12 ratio is used for dating air, water, and organic material, but is limited to only ~50,000 years.Rocks:radioactive isotope must be in rock.U238 date range: 10 million to 4.6 billionK40 date range: 50,000 to 4.6 billion