# Introduction to Geochronology/Introduction

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Radio-isotopic dating is the determination of ages of geologic materials through the comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.

*D* = *D*_{0} + *N*(e^{λt} − 1)

where

*t*is age of the sample,*D*is number of atoms of the daughter isotope in the sample,*D*_{0}is number of atoms of the daughter isotope in the original composition,*N*is number of atoms of the parent isotope in the sample, and*λ*is the decay constant of the parent isotope, equal to the inverse of the radioactive half-life of the parent isotope times the natural logarithm of 2.