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Why have geochronologists disagreed about the exact length of the Silurian Period?

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

Geochronologists disagree on the exact length of the Silurian Period primarily due to the challenges of obtaining precise absolute dates through geochemical analysis.1

The process relies on analyzing radioactive isotopes within igneous rock, but these samples are often compromised by metamorphism, which resets the radioisotope clock. Furthermore, because suitable igneous bodies are rarely found near the established boundaries of the Silurian System, researchers must extrapolate boundary ages using a limited number of data points from older Ordovician and younger Devonian rocks.1

These technical limitations have led to varying estimates, with some researchers suggesting the period lasted as little as 18 million years, while others argue for a span of up to 40 million years.1