hi! while you may get answers here, this question is worth x-posting to /r/AskAnthropology, since the answer stretches far into pre-history

The first human use of fire occurred approximately 1 million years ago in Wonderwerk Cave, South Africa. The evidence is burned bones and ashed plant remains found in situ during archaeological excavation.

This is the publication of the study which discovered this. I actually performed some of the FTIR analyses on the burned bones for Dr. Berna, while I worked in the university lab.

Berna, Francesco, et al. "Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa." Proceedings of the National Academy of Sciences 109.20 (2012): E1215-E1220.