And then we will find more energy in . . .?
I’m not sure that I understand your comment. The four hundred years is the amount of energy available in coal, if used to make electricity and converted to fuel oil (for about $60/bbl) at current rates of consumption. Coal, btw, is clearly of biological origin.
Burning coal for electricity makes little sense when nuclear energy is available, but that’s the silly political environment we find ourselves in.
Sometime in the next four hindred years, approximately the time since Columbus’ voyage, the world will have to work out the details of how to take of itself without us. The abiotic theory offers the hope that virtually inexhaustable reserves of hydrocarbons are available under the surface of the earth, if we learn how to exploit them.