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Although the age of the earliest objects from Meadowcroft remains controversial, this rock shelter 30 miles southwest of Pittsburgh has long been considered one of North America's most promising pre-Clovis sites. Among the findings: charcoal, pieces of bone and antler (some scored with knife marks) and charred fragments of basketry that are estimated to be between 12,000 and 15,000 years old. There is also an assortment of non-Clovis blades and points. Says Mercyhurst's Adovasio, who has studied Meadowcroft for nearly 20 years: "It may well be the oldest archaeological site in North America."
Bluefish Caves, Yukon Territory
Discovered in 1975 by researchers with the Archaeological Survey of Canada, these caves in the remote northern Yukon have yielded flaked stone tools that are 10,000 to 13,000 years old, what appear to be butchered mammoth bones 15,500 to 20,000 years old and bone tools from perhaps 23,500 years ago. To date, however, the researchers have been unable to find any hearths or other cultural features.
Taima-Taima, Venezuela
An ancient water hole called Taima-Taima in northern Venezuela became the deathbed of a young mastodon -- killed, apparently, by some of the first Americans. The site, excavated by Alan Bryan and Ruth Gruhn of the University of Alberta in Edmonton, appeared to contain 13,000-year-old mastodon bones, one of them embedded with a pointed stone projectile. Mixed in were stone tools and rounded pebbles that could have been made only by humans. Some archaeologists, however, believe the artifacts found at Taima-Taima became interspersed with the mastodon bones as the water level in the hole rose and are therefore much younger than they seem. Even so, there is strong interest in the site because its reputed age is close to that of Monte Verde.
Pedra Furada, Brazil
Of all the plausible places for early human settlement of the Americas, Pedra Furada, located in a region of dramatic sandstone cliffs in the arid outback of northeastern Brazil, is probably the most exciting -- and most disputed. When archaeologist Niede Guidon of the School for the Advanced Study of Social Sciences in Paris first excavated the site in 1978, she found cave paintings, ash-filled hearths and what she believes are stone tools that are at least 30,000 and perhaps more than 50,000 years old. Says Guidon: "I was the first person to be surprised. I believed the standard theories." Each successive radiocarbon test, though, bore out her initial findings. She became a convert -- and an untiring champion -- of the pre-Clovis theory.
But convincing fellow scientists has been a battle. Guidon's conclusions have been greeted with skepticism by many archaeologists. One problem, explains Randall White of New York University, is that the "tools" from the deepest levels at Pedra Furada are mixed with naturally fractured river gravel. This suggests that the geological layer was not laid down in an orderly way. The stone flakes could easily have been churned together with much older river rock before settling. Moreover, they might not be human-made at all; the artifacts themselves could have formed by natural erosion.