Christopher Columbus is widely considered the discoverer of America despite the fact that there is ample evidence to suggest that he was not the first European to reach the Americas. Before him, Norse explorer, Leif Erikson had landed in North America and even established a settlement at Vinland―the northernmost tip of Newfoundland in Canada. However, even Erikson's pre-Columbian discovery of North America may not be the first instance of humans crossing over into what we know as the New World. There exist theories which suggest that the ancestors of Native Americans crossed over into the New World several thousand years ago, most probably in response to overcrowding and resultant competition for resources. Also known as the Bering Strait theory or Beringia theory, the Land Bridge Theory is one of the most popular model of migration into the New World. It proposes that the first people to populate the Americas migrated from Siberia (Asia) to Alaska (North America) by crossing the land bridge that once existed where the Bering Strait―linking the Arctic Ocean with the Bering Sea―exists today. This migration is believed to have happened fourteen to twenty thousand years ago. ▶ When Alfred Wegener's continental drift theory was challenged by the land bridge theory, Wegener came out all guns blazing against the latter. Back then, the continental drift theory was highly criticized. Wegener argued that continents and the deep-sea floor were not made of same rock. While continents were made of granite, the deep-sea floor was made of volcanic basalt. Taking into account the difference in density of these rock types, the land bridge should have bobbed up if it were pushed to the bottom. ▶ Furthermore, the now-separated mountain ranges in Appalachia, Scotland, and Norway are known to be a part of the same range. While early humans and animals could have migrated over the land bridge, the Land Bridge Theory fails to explain the separation of these mountain ranges. But obviously, they cannot migrate. If at all, they must have drifted apart, which is exactly what the continental drift theory suggests. Interestingly, the Land Bridge Theory is one of the many theories that attempts to explain the settling of early humans into the New World. For instance, there is a theory on similar lines that suggests that Europeans crossed ice sheets covering the North Atlantic to reach North America. And there is yet another, which proposes that Southeast Asians reached North America by boats around 20,000 years ago. What's common to all these theories is that none of them seem to have a concrete explanation for the peopling of the New World.