The method that is rb-Sr on the basis of the radioactivity of 87 Rb, which undergoes simple beta decay to 87 Sr with a half-life of 48.8 billion years. Rubidium is a major constituent of really few minerals, nevertheless the chemistry of rubidium is comparable to compared to potassium and salt, both of which do form many typical minerals, so rubidium does occur as being a trace aspect in many stones. Due to the lengthy half-life of 87 Rb, Rb-Sr relationship is employed mostly on stones avove the age of about 50 to 100 million years. This process is quite of good use on stones with complex records since the child product, strontium, doesn’t getting away from minerals almost so effortlessly as does argon. Because of this, an example can obey the closed-system requirements for Rb-Sr dating over a wider variety of geologic conditions than can a test for K-Ar relationship.
This is exactly why, easy Rb-Sr many years may be determined just for those minerals which can be saturated in rubidium and have an amount that is negligible of strontium.
The calculated age is insensitive to the initial strontium amount and composition in such minerals. For the majority of stones, nonetheless, initial strontium is contained in significant amounts, so dating is completed by the isochron technique, which totally eliminates the difficulty of initial strontium. (mais…)