Simple definition of radiometric dating
Accurate measurement of either the absolute or relative abundance of trace quantities of radioactive isotopes requires sophisticated instruments, known as mass spectrometers, and instrument operators who really know what they are doing.
The technique appears to be simple and straightforward, but is actually very difficult and time-consuming.
The number of parent atoms that decay in a fixed period of time, or conversely the number of daughter atoms produced, depends on the number of parent atoms present at any point in time.
Such a relationship results in an exponential decrease in the number of parent atoms remaining as a function of time, if "time" is expressed as the half life (the length of time required for 50% of an initial quantity of radioactive atoms to break down) .
In order to use this equation for decay over a given time period, we will need the solution of a first-order differential equation.
Radiometric dating of metamorphic rocks can be successful, but often the results are difficult to interpret, and in many cases are ambiguous.In many respects, igneous rocks are the easiest to date because the starting of the clocks are unambiguous. : Sedimentary rocks are, to a large degree, made from fragments of pre-existing rocks that have been broken, weathered, transported and ultimately deposited in ocean basins.These fragments (e.g., sand or mud) may become cemented together to form sedimentary rocks.I use the term "appropriate" in the sense that the specimen to be dated must obviously contain isotopes of a well known radioactive decay series, and be suitable for precise chemical analysis.
In the simplest ideal situation,the decay equation is utilized by making the following substitutions: P = N (# of parent atoms currently present as measured inthe lab) Pand can accurately measure D and P, in principle, we can determine the absolute age.This assumption is in many cases not valid, as daughter atoms certainly existed in the mineral or rock at the time the radiometric clock started.The solution to this problem can be illustrated using the Rubiduim (Rb) - Strontium (Sr) system.The solution is: The equation above is known as the decay equation.