Since samarium-neodymium dating is somewhat easier, the lutetium-hafnium method is used less often. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. These half-lives completely agree with the half-lives measured from decays occurring today. While TL dating does not usually pinpoint the age with as great an accuracy as these other conventional radiometric dating, it is most useful for applications such as pottery or fine-grained volcanic dust, where other dating methods do not work as well. This transformation may be accomplished in a number of different ways, including alpha decay emission of alpha particles and beta decay electron emission, positron emission, or electron capture. This method has been useful for dating iron meteorites, and is now enjoying greater use for dating Earth rocks due to development of easier rhenium and osmium isotope measurement techniques.
A few experiments have found small variations in decay rates, at least for some forms of decay and some isotopes. The study of strata and their relationships thermoluminescence: This allows the dating of these materials by their lack of thorium. If the material is heated, these electrons can fall back to their original orbits, emitting a very tiny amount of light. By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as "bracketing" the age of the sedimentary layer in which the fossils occur. A carbon-based life form acquires carbon during its lifetime.