Vennemann posits that starting in the fifth millennium BCE, Atlantic/Semitidic seafaring colonizers (related to Semitic speakers) settled the coastal regions of Western and Northern Europe.
He points to Old European hydronyms (river names) across the continent, which he reinterprets as having Basque-related origins rather than Indo-European ones. Europa Vasconica-Europa Semitica
This "substrate" influenced the vocabulary and structure of the languages that eventually replaced them. Vennemann posits that starting in the fifth millennium