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Comment by a8da6b0c91d | Hacker News Reader

Industrial civilization is definitely a one shot deal. All the surface metal deposits are gone. You need massive industrial infrastructure to access the remaining ores. You couldn't even progress to the iron or bronze age after a reboot.

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>All the surface metal deposits are gone.

Well, they're not so much gone as converted into various structures all over the globe. I see no reason why later civilizations couldn't mine the remains of former cities.

Pretty much this - mining would be done on old landfill sites and cities, at least for metals. Fossil fuels are a different type of problem - we're not going to get all that carbon back. Conversely maybe a reboot civilization would develop differently - forests to solar thermal to PV and batteries. It would be slower, but certainly possible.

How are you going to do any metalwork with your scavenged metal? Heat it up with a big mirror? Its very very hard without high energy density fuel. The article suggests charcoal (did you read the article?) but thats problematic too.

Just because it would be a slower development path doesn't mean it's impossible. It would be slower, but any given civilization would have only a few viable options for development - so yes, I think you'd find a civilization which values glass and mirrors and polishing technology to get the heat necessary for metal working.

I don't think a civilization built on a shit load of aluminium scrap is going to develop very slowly. Don't forget aluminium is a wonder metal that's only been around for like a hundred years.

All really important metals can be melted at temperatures that can easily be reached with a well built furnace and natural fuel like wood.

Plus, we already know what we did to get to where we are now. We can adapt that knowledge to get back to where we are now. It's going forward we're going to be stumbling in the dark, but we're doing that now anyway.

See my reply to your comment in a sibling thread. A wood fire can hit 1050C. There's plenty of easily-available metal in that range, and building a forced-draft charcoal burner will get you to 1350C. Iron melting points start around 1150C; steel is probably out of the question, but that doesn't mean much.

> How are you going to do any metalwork with your scavenged metal?

With a wood-fired forge. Blacksmithing predates fossil fuels by quite a long time.

We can, make new hydrocarbon fuels. Grow plants that are high in fatty acids that we can run catalytic cracking processes on to make usable fuels. Or, use fermentation and the like to make alcohols from plants with a high sugar content. Again, slower, but at the same time, it would be part of the process.

You can just dry and burn the plants directly. You can replace coal almost directly with dried plants.

Indeed you can. It's definitely the simplest way of doing it. However, by pulling the fatty acids out, etc, you can also pull out a lot of other useful products, like ammonia and hydrogen sulfide. Additionally, a fire will produce a lot of ash and smoke, which both will need to be mitigated in one way or another.

Yeah, low tech wood fires are an air-pollution disaster:

http://www.samharris.org/blog/item/the-fireplace-delusion

It's possible to burn plants cleanly - you need lots of air, and possibly a catalytic converter.

Not something you would do at home, but a power plant can.

We should, today, switch from burning coal to burning switchgrass.

One of the reasons why mining the remains of ancient cities could prove to be impossible, is that a lot of the metal would get oxidized (aka rust)

In the case of rust, there are a lot of chemical similarities between it and hematite (though contamination with iron hydroxides might be a problem), which might (theoretically at least) make it potentially suitable for smelting into pig iron. I don't think any existing industrial processes do this, though.

It's not a problem to remove rust from iron. Just heat it in a low oxygen atmosphere, and add carbon which will react with the oxygen in the iron.

You do need to carefully control the amount of carbon though.

Well, depends on how you look at it. All (most of?) those metals are somewhere, aren't they? Actually there are many of those metals on the surface, there's not even need to dig for them.

Once you've got the metal, how are you going to heat it up so that you can re-shape it?

That's an interesting question, however it is not what I was replying to. I'm not sure your question should be pointed at me :)

In any case here's my quick answer: I hope they come off as Lego bricks.

Why not wood? You can easily build wood fires hot enough to work refined aluminum (all those cans, good for something!), copper (rip out the plumbing and wires en masse, it won't be pure but it'll be close enough), tin, and zinc; with copper, tin, and zinc those you can create bronze and brass. Iron would be out of the question with simply a wood fire, but--assuming other knowledge was intact, of course--you could build a forced-draft charcoal burner which can easily get hot enough to melt down some forms of iron.

When I started thinking about this problem I was expecting it to be a tough one, but I think it's achievable.

Iron and Steel can be worked on a charcoal/wood fire. Maybe it won't be easy, but the scale of malleability is basically linear with temperature. Every 100 degrees and it gets a bit softer.

Metallurgically, this won't necessarily yield the best parts if we can't reach critical temperatures - 1900°F, but even then, there are plenty of forgiving alloys out there, and plenty of metal that can be re-worked without melting it down.

The bigger difficulty in my mind is having all the alloys identified. It is pretty business even with good modern tools.

Take your wood fire, add some aluminium you scavenged from an aircraft, then add some rust.

Voila, 2500 C.

http://en.wikipedia.org/wiki/Thermite

This should be a top-level comment. There are probably other similarly low-tech ideas that could be used to bootstrap a civilization.

The problem with wood as a fuel is that any densifying human culture can burn it faster than it grows. Industrial uses compete with household uses for cooking fuel and heating. Europe in the 14th to 16th centuries saw massive deforestation in England, Germany, and elsewhere, and the state had to reserve stands of large timber as a military resource for shipbuilding. This was a significant concern in the early Tudor and Elizabethan era, for example, and the Black Forest reached its smallest extent during this time also, IIRC. Wood for fuel came from intensive coppice stands, and significant wood was imported as well.

As the article says: "Wartime gasifier cars could achieve about 1.5 miles per kilogram [of wood]." Comparing the time it takes to grow a kg of wood versus the value of moving a car only 1.5 miles illustrates the problem pretty nicely.

Wood is not a sustainable fuel for an industrial civilization, at anything like current rates of consumption.

Metals don't just vanish, they're still here in products that can be recycled.

That depends how long would it take for another civilization to arise from the ashes of the current one. Metals don't just vanish but most of them are chemically active and will in time rust, disintegrate, get absorbed by organics and pretty much vanish.

This is so far from the truth that it's not even funny.

There are tonnes of surface metal deposits, it's just you'd get shot for opening a mine there because it's in the middle of the national park.

Also, what do you call a 'garbage dump' other than a surface deposit rich in metals?

All of the metals we've ever mined are on the surface. We didn't put them back down into the mine... (or at least when we did it's the open pit variety)

How do you mine rust? Or thin surfaces of precious metals on electronics without the availability of chemicals which take a lot of fossil fuels to manufacture?

In other words, if there ever were a nuclear war affecting the whole world, the generations after will be stuck with whatever remains they got forever, baring some unexpected easy energy discovery or a resource-rich asteroid hitting the planet without wiping out the life.

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