At the height of the Ice Age, between 34,000 and 30,000 B.C., much
of the world's water was contained in vast continental ice sheets.
As a result, the Bering Sea was hundreds of meters below its current
level, and a land bridge, known as Beringia, emerged between Asia
and North America. At its peak, Beringia is thought to have been some
1,500 kilometers wide. A moist and treeless tundra, it was covered
with grasses and plant life, attracting the large animals that early
humans hunted for their survival.
The first people to reach North America almost certainly did so without
knowing they had crossed into a new continent. They would have been
following game, as their ancestors had for thousands of years, along
the Siberian coast and then across the land bridge.
Once in Alaska, it would take these first North Americans thousands
of years more to work their way through the openings in great glaciers
south to what is now the United States. Evidence of early life in
North America continues to be found. Little of it, however, can be
reliably dated before 12,000 B.C.; a recent discovery of a hunting
lookout in northern Alaska, for example, may date from almost that
time. So too may the finely crafted spear points and items found near
Clovis, New Mexico.
Similar artifacts have been found at sites throughout North and South
America, indicating that life was probably already well established
in much of the Western Hemisphere by some time prior to 10,000 B.C.
Around that time the mammoth began to die out and the bison took
its place as a principal source of food and hides for these early
North Americans. Over time, as more and more species of large game
vanished -- whether from overhunting or natural causes -- plants,
berries and seeds became an increasingly important part of the early
American diet. Gradually, foraging and the first attempts at primitive
agriculture appeared. Indians in what is now central Mexico led the
way, cultivating corn, squash and beans, perhaps as early as 8,000
B.C. Slowly, this knowledge spread northward.
By 3,000 B.C., a primitive type of corn was being grown in the river
valleys of New Mexico and Arizona. Then the first signs of irrigation
began to appear, and by 300 B.C., signs of early village life.
By the first centuries A.D., the Hohokum were living in settlements
near what is now Phoenix, Arizona, where they built ball courts and
pyramid-like mounds reminiscent of those found in Mexico, as well
as a canal and irrigation system.