What is oldest known coal source?
The first coal deposits were laid during the Carboniferous period, between 358.9 million years ago and 298.9 million years ago.
Within this period, the early Mississippian period from 358.9 to 346.7 Mya, was when the first coal deposits were being laid. During this period, coal was being laid in what is now eastern North America, specifically the Kentucky region.