I saw on UK TV recently a theory that a common style of North
American flint point was derived from the European Solutrean culture.

If there was such a crossing, language might have been carried across
as well as weapon points.

Such a crossing does not need a lift in alien flying craft. The
Solutrean people lived in southwest France Eskimo-fashion in a
climate like the modern Canadian Arctic. Eskimos before contact with
the white man often made long voyages in their skin boats, catching
fish and seals as they went, and hauling out on ice floes for the
night. Some Solutrean people might easily have made the crossing, as
there would have been a permanent pack-ice edge from Ireland to
America at the time. Getting fresh water at sea is no problem here,
as when sea water freezes, the freezing process often drives the salt
out, leaving particular parts of the ice nearly free from salt.