"nimbler modern humans who left Africa about 100,000 years ago."
This is a theory. There is no concrete evidence that states that 100,000 years ago man originated....
The Land masses were different, the sea levels were different, the ice sheets were different. It is even plausible that the Axis of the Earth was different or that the land masses as they are currently situated on the mantle were situated differently, thus allowing North Africa to be water and forested and Antartica to be warm and habitable.
Since we can't explore the landmass of Antartica, it is silly to assume that it was never inhabited nor postulate it was not the the home of mankind.
http://www.bradshawfoundation.com/journey/