Many scientists envision South America 12,000 years ago as a virgin landscape unknown to humankind. That vision is being shaken up by new evidence that people may have migrated from Asia to the Western Hemisphere much earlier than had been thought.
A theory widely accepted until recently says people first came to North America about 11,500 years ago, walking across a land bridge later consumed by the Bering Sea. They made their way south from Alaska, succeeding generations spreading across North America and then across the Central American isthmus into South America.
Now, finds at archaeological sites in South America, including one called Monte Verde here in southern Chile, suggest that people arrived hundreds, perhaps thousands of years before that.
Revisionists say a string of finds such as Monte Verde are making them rethink the timetable for America's first immigrants. Such reckoning also shakes theoretical pillars that have stood since the 1930s to help explain how people spread through the Western Hemisphere, colonizing two huge continents, adapting to strange terrains, climates, flora and fauna.
Scientists have carefully excavated the Monte Verde encampment and studied everything they have found, from plant particles to stone projectile points to a child's footprint in hardened clay.
Studies of the material are continuing 18 years after peasant farmers uncovered the site on the banks of Chinchihuapi Creek, 20 miles southeast of the city of Puerto Montt. Such scientific work is painstaking and slow. But radiocarbon dating _ analysis of sedimentary strata and long-extinct pollen samples, and other research _ have convinced Dillehay that the people were at Monte Verde more than 12,000 years ago.
Monte Verde is the most complete collection yet uncovered of evidence _ still inconclusive, hard-liners argue _ that people lived in South America as early as 12,000 to 13,000 before the present _ "B.P." in the jargon of archaeologists.
For people to be in Monte Verde 12,000 or 13,000 years ago, their ancestors probably had to be in North America by at least 13,000 or 14,000 B.P. _ at least 1,000 years before 11,500 B.P.