I don't think that fossil fuel is the only way to bootstrap up to a high-energy, high-complexity civilization. Hydroelectric generation also yields the sort of dependable, concentrated energy source you need for industrial development, and it was first built with 19th century technology. The necessary 19th century precursor technologies (steel, concrete, wire...) could be manufactured with wood instead of coal. Reservoir-backed hydroelectric dams can also serve, effectively, as a giant battery when you start trying to introduce more abundant but less steady energy sources like wind and solar.

The global potential of energy from hydroelectricity is only a small fraction of our current fossil-based consumption, though. And while wind and solar have potential resources far past fossil power, they can't expand as fast as fossils did historically. So the Fermi Paradox aspect might be that civilizations without fossils and without the self-control to limit reproduction are hobbled by cycles of Malthusian collapse. Or perhaps space-capable civilizations that didn't fall into the Malthusian boom-bust trap while still confined to one planet also don't go crazy with growth once they escape their gravity well, so they're out there but not leaving evidence dramatic enough to be seen by our current telescopes.

You can't really mine for high tech materials without fossil fuels. Hydroelectric won't help when what you need is to extract ore from a mountain.

Electrically driven mining equipment:

http://www.hitachiconstruction.com/about/media-press-release...

http://www.oemoffhighway.com/article/11224086/electrificatio...

If you just mean that it's impractical to build the electrical grid out to a remote mining site, that's true. In the present day remote mining sites typically use diesel fueled generators, now being supplemented with photovoltaic arrays in sunny regions. If you imagine a world with approximately-1940-level technology (so PV is not yet an option) and no fossil fuel, then you'd need to use something like biodiesel or ethanol instead of fossil-derived diesel.

> If you just mean that it's impractical to build the electrical grid out to a remote mining site

Yes, that was the general issue. We do a lot of mining in remote sites that don't have hydro power or any realistic way to get it there. You could use biofuels, but it's hard to imagine bootstrapping a technical society to the point that that becomes feasible without prior use of fossil fuels.

If you have a suitable river not too far away you actually can mine using hydromechanical power. [1] Turning it into electricity loses a lot, but transmission is of course easier

[1] http://www.lowtechmagazine.com/2013/01/mechanical-transmissi...

I think for this era, fungi and other consumers of decaying matter could not break down the cellulose walls of plant matter. Since then they did. It is interesting to imagine a species gaining sentience on a planet where there was no coal or oil to power from a wood-burning society of iron to steel and plastics.

I believe it was the lignin specifically which wouldn't decay in the Carboniferous period, leading to most of the fossil fuels around.

> I was under the assumption that the Earth is not likely to have another carboniferous period.

Well, we are busy recycling that one. All that carbon in the atmosphere will likely eventually precipitate out. On a geological timescale oil is renewable; it's simply that humans don't live that long. I suppose the cockroach civilization 60 megayears hence will be able to power their vehicles that way.

Or, you could be one of the few who believes the abiotic theory of oil production. I'm not one of them!

A sibling comment points out that back in the carboniferous period, no organisms had enzymes to break down wood. Nowadays, dead wood rots, releasing co2 back into the atmosphere.

I do think it's an important idea that fossil fuels should be seen as a stepping stone. They're not useful forever, but using them for too long is bad for all of us, and not being able to use them without a comparable alternative is an equally awful situation.

This reminds me of earthquakes that in retrospect might be caused by oil drilling, just to name one example.