Over time, radioactive isotopes change into stable isotopes by a process known as radioactive decay.
Some radioactive parent isotopes decay almost instantaneously into their stable daughter isotopes; others take billions of years.
As an example of how they are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale.
To get to that point, there is also a historical discussion and description of non-radiometric dating methods.
The discovery gave scientists a tool for dating rocks that contain radioactive elements.
It is not about the theory behind radiometric dating methods, it is about their , and it therefore assumes the reader has some familiarity with the technique already (refer to "Other Sources" for more information).Measuring the uranium-to-lead ratios in the oldest rocks on Earth gave scientists an estimated age of the planet of 4.6 billion years.Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.Far from being data, these dates are actually interpretations of the data.As discussed before, the assumptions influence the interpretation of the data.