Problems with isotope dating
In some cases the discovery of a rare trace mineral results in a major breakthrough as it allows precise ages to be determined in formerly undatable units.For example, the mineral those composed primarily of one or more ferromagnesian, dark-coloured minerals).A second advantage of the method relates to the fact that under high-temperature conditions the daughter isotopes may escape from the host minerals.In this case, a valid age can still be obtained, provided that they remain within the rock.Similar studies have shown that the samarium–neodymium (Sm–Nd) parent–daughter pair is more resistant to secondary migration but that, in this instance, sufficient initial spread in the abundance of the parent isotope is difficult to achieve.trace minerals may form, each concentrating certain elements and radioactive trace elements within the rock.
When single minerals are analyzed, each grain can be studied under a microscope under intense side light so that alterations or imperfections can be revealed and excluded.
In uranium–lead (U–Pb) dating of zircon, the zircon is found to exclude initial lead almost completely.
Minerals, too, are predictable chemical compounds that can be shown to form at specific temperatures and remain closed up to certain temperatures if a rock has been reheated or altered.
If the Earth’s interior were a simple and homogeneous reservoir with respect to the ratio of uranium to lead, a single sample extracted by a volcano would provide the time of extraction. No parent–daughter value for a closed system is involved, rather just a single isotopic measurement of lead viewed with respect to the expected evolution of lead in the Earth.
Unfortunately the simplifying assumption in this case is not true, and lead model ages are approximate at best.Many radioactive dating methods are based on minute additions of daughter products to a rock or mineral in which a considerable amount of daughter-type isotopes already exists.