Scientists have known about this for decades. Not only that, they know where those types of remains came from. A long time ago scientists noticed that ancient American skeletons could be divided into 2 distinct groups. One was typical Native American while another closely resembled Caucasian peoples.
They discovered that a group of ancient peoples in and around China were dead ringers for these remains and that they did travel to NA at the same time or earlier than the groups that became the Native Americans we know today.
This has been aired on the Discovery Channel last year.