Why is it difficult to date the split of Proto-Indo-European into separate languages?

Determining the precise date for the divergence of Proto-Indo-European (PIE) into separate languages is difficult because linguists have not established a reliable, objective method to calculate these "time depths" using linguistic evidence alone.12

While computational models have been proposed, they have not proven to be consistently accurate. Consequently, scholars rely on a form of "dead reckoning," which involves estimating the degree of difference between languages and comparing those findings to language families with known divergence dates, such as the Romance family.1

Because linguistic data is insufficient on its own, researchers must correlate their findings with archaeological evidence. However, this presents further challenges, as there is no single, universally accepted archaeological pattern that definitively maps to the migration or linguistic fragmentation of the Indo-European population. Scholars generally agree that the parent language likely split before 3000 BCE but probably not much earlier than 4500 BCE, though these estimates remain subject to ongoing debate and the discovery of further evidence.13