So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero.Lead atoms created by uranium decay are trapped in the crystal and build up in concentration with time.
Many authigenic precipitates of calcite contain virtually no thorium and inorganic precipitates have U/Ca ratios very similar to the ratio of dissolved uranium and calcium. Authigenic material should remain a ‘closed system’ with respect to the relevant isotopes but that requirement is sometimes difficult to maintain because radioactive decay results in damage to the crystal lattice of the host mineral.
Consequences of this ‘recoil effect’ and correction schemes will be discussed.
This means the clock is truly set at zero when zircon forms.
Second, zircon has a high trapping temperature of 900°C.
Uranium-series (U-series) analyses are an essential component of many research projects in Earth and environmental science, oceanography, hydrology and science-based archaeology.
Topics range from magma chamber evolution and volcanic hazard prediction, global climatic change through dating of authigenic carbonate deposits, human evolution through dating of bone, to the study of groundwater evolution.Thorium is not soluble in natural waters under conditions found at or near the surface of the earth, so materials grown in or from these waters do not usually contain thorium.In contrast, uranium is soluble to some extent in all natural waters, so any material that precipitates or is grown from such waters also contains trace uranium, typically at levels of between a few parts per billion and few parts per million by weight.Unlike other commonly used radiometric dating techniques such as rubidium–strontium or uranium–lead dating, the uranium-thorium technique does not measure accumulation of a stable end-member decay product.Instead, the uranium–thorium technique calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium-230 and its radioactive parent uranium-234 within a sample.This makes it especially valuable for dating these rocks, which have no fossils to indicate their age.