Radiometric dating parent daughter isotopes
There are a number of long-lived radioactive isotopes used in radiometric dating, and a variety of ways they are used to determine the ages of rocks, minerals, and organic materials.Some of the isotopic parents, end-product daughters, and half-lives involved are listed in Table 1.For example, a method based on a parent isotope with a very long half-life, such as C method can only be used to determine the ages of certain types of young organic material and is useless on old granites.Some methods work only on closed systems, whereas others work on open systems.Second, the rock or mineral must not lose or gain either potassium or argon from the time of its formation to the time of analysis.By many experiments over the past three decades, geologists have learned which types of rocks and minerals meet these requirements and which do not.The point is that not all methods are applicable to all rocks of all ages.
By the mid- to late 1800s, geologists, physicists, and chemists were searching for ways to quantify the age of the Earth.
My purpose here is not to review and discuss all of the dating methods in use.
Instead, I describe briefly only the three principal methods. These are the three methods most commonly used by scientists to determine the ages of rocks because they have the broadest range of applicability and are highly reliable when properly used.
They observed that every rock formation, no matter how ancient, appeared to be formed from still older rocks.
Comparing these rocks with the products of present erosion, sedimentation, and earth movements, these earliest geologists soon concluded that the time required to form and sculpt the present Earth was immeasurably longer than had previously been thought.