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If a series of zircon samples has lost different amounts of lead, the samples generate a discordant line.
The upper intercept of the concordia and the discordia line will reflect the original age of formation, while the lower intercept will reflect the age of the event that led to open system behavior and therefore the lead loss; although there has been some disagreement regarding the meaning of the lower intercept ages.
U at the time of sample formation must be known or calculated.
With time, Thorium 230 accumulates in the sample through radiometric decay.
U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years.
Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals.
Since the exact rate at which uranium decays into lead is known, the current ratio of lead to uranium in a sample of the mineral can be used to reliably determine its age.
The contributions of uranium/thorium and marine palynology to the dating of the Lake Wangoom pollen record, western plains of Victoria, Australia.
230Th/234U and 14C dating of a late Pleistocene stalagmite in Lobatse II cave, Botswana.
The method relies on two separate decay chains, the uranium series from Pb) leads to multiple dating techniques within the overall U–Pb system.
The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below).
Fission tracks and micro-cracks within the crystal will further extend this radiation damage network.