25,000 years ago a strip of land, known as the Bering Land Bridge, linked the continents of Asia and North America across what is now known as the Bering Straits. Although inhospitable, this strip of land supported human activity for over 10,000 years.
     Even though humans were hardier than they are now, how did this arid icy terrain support what has been calculated as being a population in the thousands? Well, oil and gas exploration may, surprisingly, provide the answer. Core samples taken from the ocean floor (the now submerged land bridge), in the process of their exploration activities, showed evidence of a fertile environment, with a variety of plant and animal life.
     So the evidence is there to support settlements, but the question remains, why stay in such a hostile, albeit fertile, environment and not complete the journey from Asia to North America? The answer may be ice sheets blocking the way. The melting of these ice sheets and the subsequent rise in sea levels could possibly have not only allowed the onward migration to proceed but also necessitated it, as the land bridge became submerged.
     This period of isolation may also account for the genetic differences between Asia and the Native American population, which, if continuous migration had occurred, should not have happened. Over thousands of years of isolation minute changes in genetic makeup occurred, with the population of the land bridge gradually evolving in a different direction.  

Edited from BioNews Texas (3 March 2014)