While there very likely were pre-Clovis modern humans in the New World, the evidence that there were humans in Brazil nine thousand years pre-Clovis is not strong. The new evidence at the Toca da Tira Peia rock-shelter is in the same Brazilian national park as the site of a previous claim at Pedra Furada alleged to be 50,000 years old by their investigators.
Skeptics have argued that the "unearthed burned wood and sharp-edged stones" dated to such ancient time periods, "could have resulted from natural fires and rock slides."
[The new] site’s location at the base of a steep cliff raises the possibility that crude, sharp-edged stones resulted from falling rocks, not human handiwork, says archaeologist Gary Haynes of the University of Nevada, Reno. Another possibility is that capuchins or other monkeys produced the tools, says archaeologist Stuart Fiedel of Louis Berger Group, an environmental consulting firm in Richmond, Va.Other researchers think that the discoveries are human-made implements similar to those found in Chile and Peru at the Monte Verde site 14,000 years ago and at another possibly as old as 33,000 years ago (the dating method for the older dates is likewise widely questioned).
The dating methods are also suspect.
Dating the artifacts hinges on calculations of how long ago objects were buried by soil. Various environmental conditions, including fluctuations in soil moisture, could have distorted these age estimates, Haynes says. . . . An absence of burned wood or other finds suitable for radiocarbon dating at Toca da Tira Peia is a problem, because that’s the standard method for estimating the age of sites up to around 40,000 years ago, Dillehay says. But if people reached South America by 20,000 years ago, “this is the type of archaeological record we might expect: ephemeral and lightly scattered material in local shelters.”
The dates of 113 putative human artifacts were made with a "technique that measures natural radiation damage in excavated quartz grains, the scientists estimated that the last exposure of soil to sunlight ranged from about 4,000 years ago in the top layer to 22,000 years ago in the third layer. Lahaye says that 15 human-altered stones from the bottom two soil layers must be older than 22,000 years."
Fundamentally, the dates are questionable because:
* There is no historical precedent for modern humans moving into virgin territory on a sustained basis for thousands of year without expanding exponentially and leaving an obvious sign of their presence. If the site showed the signs of a marginal community that lasted a few hundred years and collapsed that might be imaginable. But, this site purports to show continuous habitation for eighteen thousand years or more.
* There is an absence of intermediate sites between South America and any possible source of humans in the appropriate time frame. (There is one alleged older site in the American Southeast with similar dating and hominin identification issues).
* There is no skeletal evidence matching the remains definitively to modern humans prior to 14,000 years ago or so. Even if the dates were undisputably that old and made by hominins, in that time frame, a small band of archaic hominins with less of a capacity to dominate their surroundings might be more plausible.
* No radiocarbon dating has been possible and it is not well established that the dating method used is really accurate to the necessary degree of precision.