Widespread fire use by ancient hominids is estimated to have shown up between 400 thousand and 350 thousand years ago. I can’t access the whole article but from the abstract I suspect the research focuses on the increased scale of controlled fire use around 50,000 years ago and the fact that there was enough usage to impact the carbon cycle (consider how much lower a population they had than we do now, but their interactions with fire were already impacting the environment).