How would you use these data to calculate the geologic age indicated by the isotopes in each sample?
You can use principles of relative geologic age to determine sequences of geologic events, including rock formations, intervals of erosion, tilting, folding, and faulting like those represented in the block diagrams and cross-sections below.
For more information on these systems, see the isotopes and half-lives section of the Geologic Time Basics page.
There is a definite mathematical relationship between the ratio of the amount of daughter product isotope to the amount of radioactive parent isotope, and the number of half-lives that have elapsed.
Underlying assumptions are 1) that Faunal Succession is based on the observation that animals and animal communities that are preserved in sedimentary rocks change noticeably as geologic time passes (evolution).
It was first recognized by William Smith, a British Surveyor, who while working on open cuts of canals, railroads, and roads, noticed that the fossils change systematically from the older towards the younger rocks.
Similarly, the percentage of parent isotope percentage and daughter isotope percentage add up to 100 at all times.
The table below tracks the decay, half-life by half-life, of a radioactive isotope, and the accumulation of the daughter product isotope that the parent changes into once it decays. There are several different radioactive isotope systems that are used for measuring ages of geologic materials.
Be sure to review the principles of relative geologic age on the Geologic Time Basics page .
You can click on each of the images in Part 2 for a larger version in a separate browser window.
Superposition of rock units is a very simple and straightforward method of relative age determination.