Via New Scientist (but also Dienekes and Orbis-Quintus ), there are sets of human and animal footprints in a fossilized lava bed in Mexico dating from 40,000 years ago. The earliest arrival of Humans in the Americas is generally thought to have been as recent as 11,000 years ago, and I have seen genetic distance modeling supporting dates (of genetic isolation from the Asian forbears) as recent as 7000 years ago. The New Scientist article makes clear that the dating was done by a number of different methods and always gave dates older than 38,000.
It sounds like people in the field are waiting for an independent confirmation of the dating results. If it's confirmed, it will upend a whole lot of thinking about the peopling of the Americas.
There doesn't seem to be any idea how the people could have gotten there so long ago.
I remember seeing that the dates for initial colonization of Australia may be getting pushed back as well.
UPDATE: Thanks to Badger minor for the Australia link.