400K ago... while I have more confidence than most in our ancestors’ inventiveness, it doesn’t seem unlikely that they cooked over an open fire more often than not, so the charcoal was probably *in* the food. :”)
They didn't have a 'timer', so probably some of the food became charcoal.
I've had roasted marshmellows that were mostly charcoal and ash.
One thing I do know for sure... dental tartar doesn't come from pollution.