The Strait has been the subject of the scientific theory that humans migrated from Asia to North America across a land bridge known as Beringia when lower ocean levels – perhaps a result of glaciers locking up vast amounts of water – exposed a wide stretch of the sea floor, both at the present strait and in the shallow sea north and south of it. This view of how Paleo-Indians entered America has been the dominant one for several decades and continues to be the most accepted one. Numerous successful crossings without the use of a boat have also been recorded since at least the early 20th century.