The depletion of the earth's magnetic field is documented in scientific literature. This field shields the earth from some of the cosmic rays. The depletion of this shield has two side effects: 1) harmful biological effects, and 2) lowering the carbon-14 dates. The decay preocess is explained in terms of an equivalent circuit, providing simple solutions for the decay process. The theory and data are employed to set a limit on the age of the earth's magnet and, by inference, the age of the earth. Three independent checks provide confirmation of the theory.