Coal, yes. Iron, wouldn't the iron we moved to the surface be even more accessible? We didn't destroy it, just rearranged and concentrated it?

> Coal, yes. Iron, wouldn't the iron we moved to the surface be even more accessible? We didn't destroy it, just rearranged and concentrated it?

Might depend how long it takes: because rust is porous and friable, rusting iron should eventually degrade to nothing, and the rust would be difficult to re-concentrate then reduce back to iron.

Would whatever the rust turns into be any less accessible (ignoring availability of coal) than what we started out with though? I don't pretend to know the entire "iron cycle", but it seems like it ought to just be turning back into the same sort of minerals that we originally extracted it from?

The problem will be a lack concentrated deposits making post-collapse (and new) industrial efforts much harder. A pile of rust from one tractor in someone's back yard is not going to be worth the effort to mine and refine.

Possibly an analogous situation is the history of steel in Japan and their efforts to extract iron from sand, since they don't have significant iron ore to mine on their island.

The pile of rust that use to be a tractor, sure, that's not worth much. The pile of rust that use to be a city though... surely that's more concentrated than the rust mixed with rock (or clay) that we originally extracted it from?

Most likely not: https://en.wikipedia.org/wiki/Iron_ore, it's almost 50% iron in the worst case and can be up past 70% in the best case. The geological processes that form this ore in the mantle do a pretty good job of concentrating iron by density but it takes geological scales of time to do so and have it lifted back up through the crust. We might have to excavate a lot of earth to get to the concentrated vein of ore but when we find it it's relatively easy to chase and turn into usable iron once you know a little bit about mining and smelting as a society.

A city decayed to rust is going to be a thin layer of iron spread out over miles with some hot spots like where a building once stood (but presumably without a map of the city in this distant future scenario), but there won't be a vein of concentrated ore. Distributed rust can definitely be turned back into pure iron but the energy requirements are going to be substantially higher to do so since you're going to have to sift through much more material to collect it, more material to separate and concentrate it, more material to smelt off, and your operations will have to be more mobile to retrieve it over a larger area. That's why I think retrieving iron from our society will be more like extracting iron from ironsands (2-20% iron), and it will have similar effects on that subsequent society that sits between us now and some future point where geology has re-supplied it to the surface millions of years from now.

> Most likely not: https://en.wikipedia.org/wiki/Iron_ore, it's almost 50% iron in the worst case and can be up past 70% in the best case.

FWIW those are the ratios for the oxides themselves but the formations are not necessarily huge piles of pure oxides, if you go a bit lower to the "sources" section the lowest-concentrated formations viable for exploitation are

> Banded iron formations (BIFs) are sedimentary rocks containing more than 15% iron composed predominantly of thinly bedded iron minerals and silica (as quartz).

However that's only for post-industrial societies, at least if you have alternatives, as it requires churning through ridiculous amounts of materials.

When you don't have alternatives the ironsand article (which would be used in places with no good or accessible ore deposits e.g. japan, famously) quotes

> Sand used for mining typically had anywhere from 19% magnetite to as low as 2%.

though much like gold panning the ironsand would be sluice-separated to a concentration of 30-50% before it was further processed.

Most ironsands deposits are not considered financially exploitable to this day though, with the exception of NZ's where the iconic "black sand" beaches of north island are extremely rich in magnetite (up to 40%).

Iron rusts over historical timescales, metal deposits form over geological ones.

Am I wrong to think of metal deposits as just "rust mixed with rock"? It doesn't seem like the rock part (i.e. the details of what it is mixed with) should be critical for the extraction process?

> Am I wrong to think of metal deposits as just "rust mixed with rock"?

They're concentrated rust mixed with rocks, otherwise it's not economically viable to extract.

Like, iron is ridiculously common, relatively speaking: on earth as a whole it's more common than oxygen, for the crust it ranks 4th at 5% by mass, meaning if you went at it randomly you'd need to sift through 20kg of materials to get 1kg of iron.

Currently, we exploit formations as low as 15% iron (banded iron formations / taconite), that's the lower limit of the economically feasible, and those results in absolutely enormous amounts of tailings (waste materials).

Pre-industrialisation, unless you had no other choice (e.g. only had ironsands to work with) you really wanted to exploit natural (or "direct-shipping") ores, in the 60~70% range, the extraction is way too much work otherwise.

Sure, if you have a billion years to wait for it to all run through the rock cycle again.

The process that concentrated the iron ore we rely on does not operate anymore.

Fortunately, despite millions of tons of production every year, we are nowhere near using up the ore.

Stone coal could be, at least partially, substituted by charcoal - and often was in the past, where reachable underground coal reserves were not available.

"So by weight charcoal and anthracite coal have an energy density of about 30 MJ/kg, while poorer kinds of coal range down to half of that." (https://www.reddit.com/r/askscience/comments/udjl5/charcoal_...) However, the density of charcoal is much less than that of coal: 200 kg/m^3 vs 1500 kg/m^3 (for solid anthracite).

Producing 1kg of charcoal requires 3-4kg of wood. (Producing the 900°C for the process is an exercise for the reader.) (https://www.fao.org/3/y4450e/y4450e11.htm)

Guess what we do most of our iron smelting with?

Primitive iron smelting was done with charcoal, I believe. Correct me if I'm wrong.

Yes. Being stuck at that point would be the problem.

Would it? Most new smelting plants today in the US (any built in the last few decades) use a mixture of hydrogen and carbon monoxide as the reducing gases (natural gas primarily as feedstock, but no reason it couldn’t be about 90% hydrogen produced via, say, hydroelectricity or wind).

Coal didn’t overtake charcoal for smelting iron in the US until the latter half of the 19th century, well after the first industrial revolution.

Melting down scrap iron is one of the main sources of steel in the US, and that is done straight with electricity in arc furnaces.

Coal accelerated the second industrial Revolution, but it was not essential. Far more important for enabling the first industrial Revolution was some of the early scientific knowledge about steam and pressure, such as the work of Robert Boyle, a lot of that based on a sort of reaction to the classics that had been revived in the Renaissance. The biggest argument for coal is indirectly in that it helped the viability of British society (after the island had most its tree cut down over the previous 500 years) which played an important role in the Scientific Revolution (Robert Boyle was Anglo-Irish)… although by the time Britain was playing an important role, the scientific Revolution was already underway on the mainland of Europe. As long as our books are not all destroyed, I think we’d have no problem bootstrapping from charcoal the second time around.

(I think a lot about long term data storage… writing in stone or fired clay still seems like one of the best methods for writing that needs to last 10,000 years… it was, after all, preserved Greco-Roman classics that enabled the renaissance and therefore the scientific Revolution.)

I think that vastly underestimates the dependency tree in modern society. Storing hydrogen in useful quantities is tough, requiring fairly sophisticated metallurgy and cryogenics.

Finding out we've got a hard to replace left-pad module somewhere far up the tech tree wouldn't be fun.

The dependency tree of 19th Century or early 20th century society is a lot more straightforward, however.

And no, you don't need such sophistication for storing useful amounts of hydrogen. Storing large amounts of hydrogen (in this case, also mixed with poisonous CO) was solved in the beginning of the 19th Century (well, late 18th century) in Britain and Germany by using very large near-atmospheric storage vessels called Gas Holders: https://en.wikipedia.org/wiki/Gas_holder

Salt caverns can also be used for greater volumes, i.e. for seasonal storage, as are already used for hydrogen storage in a few places in the US and elsewhere. https://en.wikipedia.org/wiki/Underground_hydrogen_storage

Except the Iron Age started around 2000 BC, so the world would largely be without iron for a very long time.

That gas holder article says they contained methane or coal gas. Methane's density is 0.657 kg/m³; hydrogen's is 0.08375 kg/m³.

Coal gas is a mix that (by energy) is about half hydrogen, as I said. And hydrogen gas a specific energy of 142MJ/kg vs 55.5MJ/kg for methane.

Or instead of stone tablets you could simply build a 10,000 year clock.

https://www.businessinsider.com/everything-you-need-to-know-...

Yeah, I think we switched to coke during the Industrial Revolution not because it's a better fuel than charcoal, but because we were running out of trees.

Coke was Abraham Darby's doing (around 1709-1710), and that was mostly to corner the market for cheap pots and kettles. There was no way for the charcoal crowd to compete on iron, and the bronze bunch - the norm for that sort of thing up to that point - was left forever in the dust.

What?

I think it might be helpful to consider what happened to the dinosaurs. The same could happen to us if we fail to evolve in time...

Asteroid hits. Wipes out almost all life. A million years later, the biomass around us will have all been converted to a black ooze (oil), covered by millennia of rock, sediment, and tectonic plates. Eventually future civilized beings who plunder the Earth for our biomass that has been converted to oil and coal discover uncanny hard-to-explain remnants of a past civilization of, get this, bipedal animals.

Coal and oil formation would not occur due to lifeforms able to digest trees. It would be extraordinarily difficult to reset to those primordial conditions. I don't think an asteroid hit could do it.

Are you sure about this? I actually looked into this not too long ago and that theory no longer seems well supported.

Oil forms when sea plankton and algae are buried and exposed to high pressures and heat. Coal forms when dead plant material protected somehow from biodegredation (say by mud) forms peat and is then buried, and exposed to high pressures and heat.

I was also surprised to learn that the inabality of fungus and bacteria to degrade lignin is unlikely to have been a key driver of coal formation during the Carboniferous period, instead it was "a unique combination of everwet tropical conditions and extensive depositional systems during the assembly of Pangea".

Source: https://www.semanticscholar.org/paper/Delayed-fungal-evoluti...

Are you suggesting if the dinosaurs had tried harder to "evolve in time", they could have better survived an asteroid hit? I don't think that's how evolution works. For humans either.

Humans could most certainly survive an asteroid if the humans worked at the technology and industrial capacity to do so. Including technology and industrial capacity involved in redirecting asteroids: https://www.youtube.com/watch?v=g7zdeQ-Uw8k

(To redirect Chixculub would require a MUCH larger capability, probably on the order of 10 million tons in orbit, but that's possible with a fleet of large reusable rockets capable of getting the cost to orbit down to around $10/kg, or equivalent development of in-space resource utilization capacity.)

You assume we would be able to organize the social, political, and financial impetus to take on a task like that in a unified way that has a chance to succeed. Recent events seem to say that we are at least as likely to just fight about it until the asteroid hits.

For greatest success I think there would need to be two but probably not many more than two major efforts going on simulatneously, in much the same way that CMS and ATLAS experiments at CERN were independently looking for the Higgs. If one fails for some unforseen technical reason, the other might not if they took a different approach.

> Are you suggesting if the dinosaurs had tried harder to "evolve in time", they could have better survived an asteroid hit?

Well, yes. It's not fair to the dinosaurs, I admit. They hardly had a chance to develop language and mathematics. They were still too busy ripping each other's faces off. And not having opposable thumbs, of course, really put a damper on technological development. Maybe in a another million years things would have been different, but the asteroid had a different idea.

We, on the other hand, are at least on the precipice of the capability to divert asteroids. Hopefully we don't get an asteroid visit too soon.

I think it's a misconception that we can somehow speed up or direct "evolution", no matter what language and mathematics we have.

Diverting an asteroid, however, is not evolution.

Of course you can speed up and direct evolution, it's called artificial selection and it's how we got dogs, cattle, and almost all crops.

One thing I sometimes wonder is: if there was a dinosaur species which had reached roughly our level of intelligence and society, would they have left enough of a mark on the world that we could even tell?

If they got further than us, tried to capture an asteroid and mine it, could they have wiped themselves out without leaving behind technosignatures that would still be visible?

This is called the "Silurian hypothesis" and is named after the Doctor Who episode that showed an advanced dinosaur race called the "Silurians" that went into cryo millions of years ago.

Some real geologists explored the idea (someone could find the paper and subsequent news articles) and I think the conclusion was that on geological time periods, there might not be much left for us to find.

Yep, the [paper's conclusion](https://ntrs.nasa.gov/api/citations/20200000027/downloads/20...) was just as you said, there'd not be much of a record to find for civs older than 4 Ma. Also, there are past anomalous and abrupt events in the geological record that appear similar to byproducts from our anthropogenic activity. Evidence against is that timing for majority of such anomalous events can be matched to mundane geological activity in the record.

The rate at which we're accumulating change compared to geological record is also a strong argument against, although they argue limitations in current dating methods reducing how much can be said with certainty about prior epochs.

While there is precious little reason and evidence to believe a priori in a previous advanced dino civ, there are studies that could be done on sediment data that'd lend more certainty (such as looking for unusually rapid metal production).

> Anthropocene layer in ocean sediment will be abrupt and multi-variate, consisting of seemingly concurrent-specific peaks in multiple geochemical proxies, biomarkers, elemental composition and mineralogy. It will likely demarcate a clear transition of faunal taxa prior to the event compared with afterwards. Most of the individual markers will not be unique in the context of Earth history as we demonstrate below, but the combination of tracers may be. However, we speculate that some specific tracers that would be unique, specifically persistent synthetic molecules, plastics and (potentially) very long-lived radioactive fallout in the event of nuclear catastrophe. Absent those markers, the uniqueness of the event may well be seen in the multitude of relatively independent fingerprints as opposed to a coherent set of changes associated with a single geophysical cause.

My opinion is this ultimately boils down to how hard human level intelligence is to evolve, which is why the hypothesis is interesting in the context of the Fermi Paradox. Intelligence might be extremely difficult to evolve, it might require an unusual background environment set of condition or just might not be that useful in general.

Pretty sure all the radioactive ore refining we have done is going to leave a mark for billions of years. Never mind how we’ve displaced large percentages of the readily available rare earths already.

I doubt the dinosaurs shuttled away or buried all their geo-engineering marks.

Schlock Mercenary is a sci-fi webcomic with a fun thread about sapient dinosaurs fleeing Earth pre-impact.

There's no good way to read just those strips, but it starts here:

https://www.schlockmercenary.com/2018-07-25

While our time has been short on geological scales, that's a point in favor of being discovered later. So much has been deposited by us in the geological record in a stunningly short (by future geologists' viewpoint) timescale like plastics, temperature variations, and irradiated patches of land.

To make things worse for a hypothetical advanced dinosaur species, if they were at the point they could capture an asteroid, they would be roughly equivalent or better with us but we could survive an asteroid extinction event just fine. Society as we know it perhaps wouldn't survive but an event that could genuinely end us as a species would need to be exceedingly destructive or long term. Otherwise the remnants will rebuild, give or take a couple 10s of thousands of years, which is basically nothing on the timescales we're thinking about here.

Humans left a ridiculous amount of stone tools which last basically indefinitely in the fossil record (and unlike bone fossils, don't require super special conditions to preserve them). So I think we'd have enough evidence from modern artifacts made of similar types of materials. A car buried under sediment would rust all out, but you'd be left with a big car-shaped bunch of rust as well as chunks of pure metal which better resist corrosion, like stainless bits or the platinum catalytic converter, various bits of glass and ceramic in very artificial looking shapes, etc.

Maybe the archaeologists of the future would weave scholarly narratives as to how these ferrous-based lifeforms lived, what their diet was and how they came to perish.

Film-makers would use stop-motion techniques to depict battles between Fordusprefectops and Chevroletcamaro-Rex whilst their own early ancestors look on, clad in loincloths and bras made from footwell mats.

https://news.ycombinator.com/item?id=29302827 "cars are the dominant species, since so much of our world has been dedicated to them"

Like in David Macaulay's "Motel Of The Mysteries".

I'm not sure I buy this. The main driver of the industrial revolution was intellectual: the emergence of science, classical liberalism, mercantilism, and modern economics. All this was in place before anything really took off.

Industrialization without fossil fuels would scale much more slowly with wood being used at first and then probably crops being grown for energy (biofuel). Once we figured out electricity we'd have large scale hydropower and wind power. Then we'd figure out either photovoltaics or nuclear fission, at which point we'd be off to the races. My guess is we'd be almost 100% nuclear and hydro powered right now with use of photovoltaics growing.

Stable power grids would probably take longer to emerge, but we figured out simple rechargeable batteries (lead-acid) fairly early. People would probably have banks of these in their homes to power minimal lighting and things like radios, TVs, etc. at night and run their appliances at specified times when the grid was at high power. You'd probably see a food system less dependent on refrigeration until stable grids emerged.

On extremely long historical timescales I suppose depletion of other elements is possible, but things like iron are incredibly common in Earth's crust. I'd be concerned more about rare elements.

> One of the interesting possibilities for the Fermi Paradox is the fact that we've wiped out the readily accessible deposits of iron, coal, oil, etc. A second go at the industrial revolution would be much harder, if we regressed that far.

It’s odd to me that we don’t see this specific point discussed all that much. Sure, it comes up here and there now and then, but I think it deserves an extended discussion. My understanding, based on what I’ve read about this implication, is that we as a human species only get one chance to evolve beyond the gravity well of our planet. If we fuck this up, and by all accounts it looks like we are, we will be condemned to extinction on Earth.

I doubt that. There's plenty of Iron that doesn't require mining to find, and it naturally accrues in the environment over time: https://en.wikipedia.org/wiki/Bog_iron

We stop mining coal when it is no longer economical to do so, not when the mine is entirely depleted. There's a bunch of coal at or near the surface and will be for quite some time.

The same goes for Oil. We extract that which is easiest to extract and fraction into the products we desire, preferring to leave things like the energy intensive and more polluting "Tar Sands" behind.

Japan has very low quality iron ores. Yet they turned out (arguably) the best steel swords in the world.

Constraints don't always lead to bad outcomes.

Japan definitely produced some of the most beautiful looking swords, and they are extremely impressive given the quality of iron they are forged out of, but I don't think any sane person would choose one to take into battle given any other option.

Friend is a hobbyist blacksmith and he said it really well.

Japan developed their hugely overdone turned-steel technique because the ore they had to work with was so bad: hammering the garbage out was the only way to get the quality of the steel itself into acceptable levels. As a result, Japanese smiths developed something very close to what we'd now call layered steel.

European swordsmiths (think: Toledo) had access to higher-grade ore, and as a result never needed to develop techniques to work around fundamental problems with their source material.

This is my point. Constraints sometimes take us to places where we otherwise wouldn't have gone.

The world is (imho) a better place because Japan has bad iron ore. If that wasn't our reality, we would never have guessed it.

I am confused. Are you saying that the quality of the iron makes them shit swords, or that guns are better than swords?

It would depend a lot on what time period you're talking about. I'm not an expert, but I do a bit of amateur forging and have learned a couple of things just reading about this craft. By the 14 or 1500s, spring steel had been developed in Europe. This would enable a sword to flex rather than break. Japanese swords from the time weren't flexible and were generally more prone to breaking. This had a lot to do with the raw materials that were available. They also tend to have softer mild steel core to help with this problem, with a very hard and sharp edge. If the entire blade were made of the same material as the edge, it would be extremely inflexible and brittle. They're kind of designed in a way where a part of the every hard and brittle edge can crack, but maybe it won't extend all the way up through the blade leaving it somewhat usable. The European longsword from the time might just flex in the same circumstance.

That's not to say that European swords were better than Japanese swords in every way. This is one of many, many factors. And I'm sure there were plenty of crappy longswords at the time (and crappy katans), so you kind of also have to decide if you're comparing the best examples, average examples, or low quality items as well. The skill of the wielder is also important. If you're throwing out a bunch of random soldiers without a ton of training and giving them a sword, you might want to give them something they're less likely to break. My understanding that is there was a period in Japan where only samurai were allowed to carry swords (if my reading is to be believed), who were generally very skilled. They would probably know how to avoid putting their blade in situations where it would be prone to breaking.

And Japanese traditional Japanese sword making techniques are extremely impressive and interesting to read about given the materials that were available at the time.

From what I've heard and seen the quality of metal makes them prone to breaking, and you need skill to take full advantage of the razor sharp edge. I have seen a great video showing katana students cutting bamboo and struggling and then a master going clean through that I wish I could have found again. For the record I don't think they are shit swords, just they look really cool and that has lead to various media elevating their superiority to other swords beyond reality.

I thought Japanase steel wasn't all that impressive in absolute terms, rather it was impressive because of the very bad quality ingredients they started with. It also made ownership of a sword (katana) and accompanying paraphernalia only accessible to a small caste of elite warriors. Both the raw materials and the process were hard to come by.

My understanding is that historically the best steels were made in India/Southern-India where wootz steel comes from and that for more than 2000 years the rest of the world was almost bargain tier in comparison. To the degree that samples of wootz steel were brought back to Europe even in the 18th century in an attempt to replicate the process.

I'm only an amateur metalworker though so I hope someone more knowledgeable can correct any errors.

The pre-modern/medieval Japanese iron industry was actually quite massive! We went to a museum in Izumo and there was a nice map showing the are in ancient times and now and the difference was pretty stark - there were just swamp where the Izumo city is today and the local lake Shinji was like twice as big as today.

All the new land and end of the swamps is apparently the result of hundreds of years of iron ore mining in the nearby mountains. So even with primitive means and shitty ore, if you need the material and go at it for centuries, you can achieve substantial results. Not to mention reclaim some land as a result. :)

Also in related (but much more recent development) there were coal mines in Japan mining from under the seabed via tiny islands!

Hashima is the most extreme example, basically a piece of barely dry rock that has been converted to a concrete city housing many thousands of workers and their families: https://en.wikipedia.org/wiki/Hashima_Island

But there were other such mines, some of the local ones even connected to Hashima via the underground works!

There's a difference between "we have to do more refining to get usable metal" and "there's literally none around unless you go deep underground into a new deposit".

The buried and overgrown remains of any modern junkyard, port, railway depot or rubbish dump would be a decent shallow ore for many metals. During the industrial revolution we have consumed almost all of the shallow fuels, but we haven't consumed any metals, they're right here on the surface and more accessible than before - it's just that they're currently tied up in some products or structures we use.

A sword is a tiny amount of metal compared to, say, a steam engine. Or a battleship.

Japan fielded armies of hundreds of thousands of men, all equipped with swords. I guess if you totalled the weight on metal on them, you could cobble together a battleship. But it's not really about quantity, more quality of the ore.

And the point isn't about that. The point is that the constraint (bad ore quality) forced the Japanese to get better at metalworking. Resource constraints aren't as bad as we think, because we're used to making things without those constraints. But our descendants, having always had those constraints, will find better ways of solving them than we can think of.

Hundreds of thousands? The battles I read about maybe reached tens of thousands, and who knows how many had swords.

Even in Europe, a large part of the armies were peasants with whatever comes to hand. Their resource constraint on metals wasn't the ore, but the availability of the enormous quantities of wood required to process it.

Wikipedia says 400,000 samurai: https://en.wikipedia.org/wiki/Samurai#:~:text=In%20the%20187....

Every Samurai had at least two swords. So at least a million swords. Let's say a sword weighs 1Kg, that's 1000 tonnes of steel. So probably not enough for a battleship, but maybe a small destroyer.

> arguably

Experiment: <https://youtu.be/ev4lW0wbnX8?t=1245> (German audio track, machine translated subtitles in English available)

The question is whether this settles the argument or stokes its flames.