Why is the coastal crossing theory of migration hard to prove or disprove? there are many early human sites that provide clues about migration. the coastlines that migrants would have sailed along are underwater. sea levels have lowered since the ice age. the climate has remained the same since the ice age.

The correct answer is "There are many early human sites that provide clues about migration".

The theory of early settlement, or preclovis theory, is actually a series of studies and relatively recent archaeological, linguistic and genetic findings that question the classical theory of the late settlement of the American continent based on the clovis culture, and have generated a sound debate international on the subject.

Strictly speaking, it is not a theory, because the scientists involved do not have a common position on the origin of man in America, nor do their results seem to lead linearly to a coincident response. But all of them have in common the fact that they are incompatible with the oldest date proposed by the theory of late settlement (clovis): between 12,000 and 14,000 years BP.