This half-life is so long that the Rb-Sr method is normally only used to date rocks that are older than about 100 million years.

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Understanding the isochron diagram is the key to determining the age of a rock using the Rb-Sr method.

There's a small amount of radioactive carbon-14 in all living organisms.

All of the dating methods rely on the fundamental principles of radioactive decay, but the specific materials that can be dated and the exact procedures for calculating a date are very different from one method to the next.

The rest of this activity is about using the Rb-Sr method.

Each mineral separate will yield the composition of that particular mineral.

Other Steps There are other steps that must be carried out to prepare a sample for analysis by a mass spectrometer, such as converting the sample to a solution by dissolving the mineral separates in selected acids, using techniques of column chemistry to increase the concentration of the small amounts of Rb and Sr in the solution and then precipitating the concentrated solution as a "salt" compound.

Therefore, a highly weathered rock may yield unreliable age information. Crush the rock and separate the Rb-bearing minerals.

Getting a Rock Sample Ready for the Mass Spectrometer For reliable age determination, careful sample preparation is an important and often tedious process.

The Geologic Time Scale was originally laid out using relative dating principles.