The basic run-down: A type of tool known as the western stemmed projectile point has been routinely found in contexts (or with obsidian hydration rinds consistent with) and age of up to 10,500 years ago. At Paisely Cave, these points have been found in contexts that appear to date to up to 13,000 years ago (depending on the calibration used for the radiocarbon dates), indicating that they are older then had previously been thought, and may indicate a separate cultural tradition existing simultaneously with Clovis. At the same time, new dates on coprolites (ancient human feces*) taken from the cave suggest occupation beginning by 14,300 years ago.
So, pretty old shit...literally.
Stemmed points, from the University of Oregon's website
When the dates were first released from coprolites several years ago, there was, of course, a good deal of debate regarding whether or not the ages were legitimate, and the possibility that the samples had been contaminated was raised. While this appears to have annoyed the researchers at Paisley Cave, it is a legitimate point, and one that needs to be dealt with (and, it should be said, it appears that they have dealt with it).
This got a fair amount of press coverage, and there are, of course, many statements in the press (some by the researchers themselves, others by over-eager reporters) to the effect of "these findings put the nail in the coffin of the Clovis-first hypothesis!"
No, they don't. Understand, I believe that the Clovis-first hypothesis is flawed, and I did before data started coming out that really put it into doubt. But with every individual piece of data, there is the possibility of flaws - ranging from corruption of the data source itself to mis-interpretation of the results. No one piece of data puts the nail in the Clovis coffin. That was the case with Buttermilk Creek, and it is the case with Paisley Cave.
What is making the Clovis-first hypothesis less and less tenable isn't any one result. Rather, it is the fact that results that are in disagreement with the hypothesis continue to show up. It is also the fact that there is no known Old-World precursor to Clovis, making it unlikely that the Clovis culture appeared spontaneously in the Americas - it is much more likely that people already living here developed the material culture that came to be known as Clovis after the migrated to the Americas from Asia.
Clovis points uploaded to Wikimedia Commons by Bill Whittaker
It is a pretty exciting time to be a North American archaeologist.
More interesting that the data supporting pre-Clovis occupation of the area is the data that suggests that the Western Stemmed Tradition may have developed around the same time as, and in paralel with, the Clovis tradition. This would indicate the possibility of two very different identifiable cultural groups** occupying the Americas, which may suggest that there are artifactual signs of the multiple waves of migration currently suggested by genetic evidence (looking at the types and distribution of genetic markers in the Americas suggests that people arrived here from Asia over three different periods of migration). That being said, this is the early stages of such a hypothesis, and any of a number of different types of data may surface that kills the hypothesis before it can grow.
Still, once again, it is a pretty exciting time to be a North American archaeologist.
*Remember, archaeology is glamorous and exciting...even when you are dealing with fossil turds.
**It should be remembered that both Clovis and Western Stemmed traditions indicate tool types, not people. It is fair to think that the makers of the Clovis points all derived from a related cultural group, and the same of the Western Stemmed manufacturers. However, these were likely not monolithic groups, and the spread of the tools likely represents the spread of increasingly schisming cultural groups. So, just because people in New Mexico and in Texas used Clovis points, doesn't mean that the peoples in these areas would recognize each other as being kin. These tools let us identify the peoples as different, but the people making and using the tools likely saw themselves as having little but their tools in common.