When and how did humans first arrive in North America?

Many scholars estimate the population of the Western hemisphere to have been between 30 and 60 million people prior to Columbus's first voyage. Some put the number as high as 80 million, a figure equal to Europe's population in 1500! Most of this Indian population resided in Central and South America. The population of North America was considerably smaller, since cold winters and scarcer food supplies greatly reduced the number of people who could live in this northern environment. Three to six million Indians probably lived in North America. (Some scholars estimate a population as high as ten million.)

Estimates as to when humans first began to inhabit North America differ widely. Some scholars believe that human habitation of the Americas began as early as 35,000 years ago. Other scholars believe that it began approximately 12,000 years ago. Anthropologists and archaeologists continue to study and debate this controversial issue of the beginnings of human settlement in the Americas.

The first Americans crossed from Asia to Alaska on a land bridge into present-day Alaska. Because the more of the world's water was frozen in the polar ice cap, the water level of the world's oceans was much lower. As a result, a land bridge connected Siberia and Alaska, which are now separated by the Bering Strait. Scholars call the area around this land bridge, which is now submerged, Beringia.

The earliest migrants to North America were hunters, who depended on big game animals for their survival. Approximately 15,000 years ago, the world's temperature began to increase. After the most recent ice age ended, approximately 9,000 years ago, Indians spread to other portions of the Western hemisphere. The world's oceans rose, submerging some of the Indians' original North American homelands, but, as glaciers receded, new lands became habitable farther to the south.

Climatic changes enabled Indians to spread quickly throughout the Americas, traveling along the western coast of North and South America in boats and settling from Alaska to Tierra del Fuego, the southern tip of South America. They also migrated eastward, inhabiting diverse environments ranging from the west coast to deserts, mountains, plains, and woodlands