[ch4s3]

That seems true if you only think about coal, but we started with wood and any future world without people would have a ton of that. Whale oil too would also be available. Depending on the time periods we're talking about, there would be a LOT of oil wells that could be discovered via the crumbling infrastructure left behind. Surface level coal my be gone in most places, but large mines full of coal site idle in a lot of places now for economic reasons, and energy poor society may dig out these deposits. On the scale of millions of years, there could well be additional hydrocarbons produced, and methane could be used by some future sapient organisms.

[tivert]

> That seems true if you only think about coal, but we started with wood and any future world without people would have a ton of that. Whale oil too would also be available.

I think the point is you can't go far with those fuel sources (e.g. you can't have a trucking industry that runs on whale oil).

> Surface level coal my be gone in most places, but large mines full of coal site idle in a lot of places now for economic reasons, and energy poor society may dig out these deposits.

How deep? In a thousand years (let alone a million), will the mining tunnels have collapsed and/or filled with water? Even if the tunnels still exist and are serviceable, an "energy poor society" is probably not going to pump out the many millions of gallons of water needed to get at the coal.

Current humanity has shown very little capacity for heavy investment with only a long range payoff (say taking 100 steps at a time vs. 1 or 2 steps). The problem is with removing all the easily extractable energy resources is that, is it puts the remaining ones too many steps out of reach for someone starting at square one. If you've got 2 6-sided die and someone has to roll 100 with them to get to the next step, it's never going to happen.

[ch4s3]

> I think the point is you can't go far with those fuel sources (e.g. you can't have a trucking industry that runs on whale oil).

Yeah, that's true but you can have electric trains and trams. Canals and sails are also totally useful for a coastal society.

> How deep? In a thousand years (let alone a million), will the mining tunnels have collapsed and/or filled with water? Even if the tunnels still exist and are serviceable, an "energy poor society" is probably not going to pump out the many millions of gallons of water needed to get at the coal.

In the US alone, they're all over the place. There's 250 billion short tons of coal that's estimated to be commercially recoverable in the US today. A good bit of that isn't particularly deep. There's still surface coal all over West Virginia. A lot of of it just gets left around because its too dirty to burn under current law, or is a little to disperse to mine profitably in current energy markets.

Pumping isn't that hard if labor is cheap, the Romans did it with two cylinder pumps, person powered water wheels, and screw pumps. Pumping water is actually a key challenge that leads to important technology, or it did for us.