Up in WA state they found remains that dated roughly 9,200 years old, but the skeleton has been tied up in legal battles with the native tribes and the location on the banks of the Columbia River covered up due to the Native American Graves Protection and Repatriation Act.
Even though first studies show that this human was Caucasian and probably came across on the land bridge, he's been taken away from scientists for further study and has been tied up in court since 1996. Especially since some pagan norsemen came down and claimed him as their ancestor as well.
http://en.wikipedia.org/wiki/Kennewick_Man
So I do think the land bridge existed at some point, or maybe the continents were closer/connected at that point in history.
