They didn't, and if we go there we definitely have enough carbon to go back to the Pleistocene epoch. Antarctica is believed to contain large coal and oil fields but they have not been thoroughly mapped as they are not economic to reach at the moment.

I recall watching an old 50s documentary on Antarctica when I was bored years ago and they mentioned that there was enough fuel there to satisfy our energy needs for hundreds of years. This was before anyone was very worried about CO2.