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How did radiometric dating make it possible to assign numerical ages to the Cambrian Period?

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Cambrian paleogeography — Cambrian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cambrian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

Radiometric dating made it possible to assign numerical ages to the Cambrian Period by providing a quantitative method to measure the time elapsed since the formation of specific geologic materials, moving beyond the limitations of relative dating.1

This process relies on radioactive decay, where radioactive parent isotopes transform into daughter isotopes at a constant, known rate. By using a mass spectrometer to measure the ratio of these parent and daughter atoms within a sample, geochronologists can calculate the absolute age of the rock or mineral.21

For the Cambrian Period, this has been achieved by analyzing suitable materials, such as zircons found in volcanic ash beds. Because zircons are highly resistant to chemical change and retain their isotopic signatures even under high temperatures, they serve as reliable "clocks" for dating igneous rock crystallization. By interlinking these precise radiometric ages with biostratigraphy—the correlation of rock layers based on fossils—scientists have successfully incorporated numerical estimates into the geologic time scale for the Cambrian.3451