People Migrated from Asia to the Americas
From the beginning of history until about 500 years ago, the peoples of the Eastern Hemisphere and Western Hemisphere had almost no contact with each other.
Some Chinese missionaries may have reached Central America in the 400s A. D. Daring Viking explorers landed at several places on the coast of North America around the year 1000. However, accounts of their voyages were not well known, so the journeys were not followed up by others. Old European maps showed a vast blank space or fanciful islands where the Western Hemisphere lay. In fact that vast region of the world was already densely populated.
The Great Migrations
While the Ice Age still gripped the earth, people migrated from Asia to the Americas across what is now the Bering Strait, off the coast of Alaska. This strait is the narrowest point between the continents of Asia and North America. At several periods in the past, there was a "bridge" of land there. Even when there was a water barrier, the strait was only a few miles across and could easily have been crossed by small boats.
There was neither a single large migration nor a continuous flow of people from Asia. Rather, there was a series of waves of different peoples on the move. Changes in the climate in Asia may, from time to time, have forced people northeastward and across the strait. From there they would move southward toward warmer climates. Finding some areas already inhabited by those who had come earlier, they would move on, looking for a favorable place to settle.
These migrations took thousands of years. The remains of some of the early people have been found and studied. Archeologists have found remains in western North America that may date back almost 30,000 years. The people were hunters who lived in caves and hunted the giant bison, or buffalo.
Some people moved into the eastern and central areas of North America. Others drifted farther south, through Mexico and Central America and across the narrow Isthmus(地峡)of Panama. From there all South America was spread out before them.
About 14,000 years ago, some groups moved eastward into what is now Venezuela. However, the rain forests of the Amazon River basin made it difficult for people to penetrate farther into the eastern bulge of South America. Instead they kept moving to the western shoreline, pushing ever southward. Some groups settled in the Andes Mountains. Others kept moving until they could go no farther eastward into what are now Brazil and Argentina, or southward into what is now Chile.
The Development of Agriculture
The earliest traces of farming in the Western Hemisphere have been found in south-central and northeastern Mexico, along the coast of Peru, and in the southwestern United States. The first farmers planted sunflowers (for seeds), corn, beans, squash, and a variety of other crops. In the highlands of Peru the potato was the most important food. In South America and on the islands of the Caribbean, various root crops were planted, mainly manioc and other crops that were similar to sweet potatoes.
Farming began at about the same time in both hemispheres but was adopted more gradually in the Americas. The plow was not invented in the Americas partly because animals large enough to pull it did not exist there. For the same reason the wheel was not invented either. Without the plow it was not possible to plant crops on grasslands. As a result, farming had to be done on forested land that was first burned to clear off the trees. Fertilizers were also not known in this early period.
Nevertheless, agriculture was productive enough to support village life and the beginnings of towns. By the time of the arrival of Columbus in 1492, tribes as far north as the northeastern United States and Canada and as far south as Argentina were largely

A. Y
B. N
C. NG