27 ms·

Not just oil, we probably wouldn't have an an iron age without access to unmolested surface deposits. Iron, tin, copper. If there was a pre-human civilization

by soneil 9y ago

Not just oil, we probably wouldn't have an an iron age without access to unmolested surface deposits. Iron, tin, copper. If there was a pre-human civilization, they couldn't have gone beyond the stone age, else they'd have consumed the resources our iron age depended on.

cc439 9y ago
The problem with that line of thinking is addresses in the article. The oldest large scale area of "ancient" crust on land is a mere 1.8 million years old (the Negev Desert). The entire surface of the earth is regenerated on a scale of tens of millions of years, any depletion of surface deposits which occured ~100 million years ago would have long since been hidden by the replenishment of new crust provided by plate tectonics.
- soneil 9y ago
  I don't believe it covers that at all. I believe their definition of crust there is a lot more superficial than it sounds like. eg, the Chicxulub (Yucutan) crater is 66 million years ago, and clearly hasn't been recycled else we wouldn't be looking at it. We have dinosaur fossils dating ~230-240 million years, so the crust clearly hasn't been recycled that thoroughly. Indeed, the entire Pangea theory would be invisible to us if the continents didn't remain 300+ million years later. (I'm not saying we should have a fossil record of 'the others', as the article says, there's a survivor bias in fossils. Just that the fossils we do have wouldn't exist if the crust has been geologically renewed in the last few millions of years.) They're talking about surface markers like roads and buildings. To replace a previous civilization's trashheaps with geological mineral seams, you'd need to pre-date Pangea.
BurningFrog 9y ago
Unless they shipped the metals off planet, that's not really an argument. If anything, an iron using civilization would have made iron more concentrated and easier to find.
- scottie_m 9y ago
  Aluminum sure, but iron rusts. In tens of millions of years you could have oxides of iron from a civilization, but no workable steel or iron. Aluminum might survive, gold and platinum would be fine, but not iron. It doesn’t matter though, we’d have gone through many cycles of subduction and renewal in such a long time, so we’d have new surface deposits. Coal and oil would even have started to form over such a long time scale.
  - PeterisP 9y ago
    What do you mean by "workable steel or iron" ? We're not mining for steel, and it's not like iron age started with finding some magic store of "workable iron" instead of iron oxides - the surface iron and mined iron deposits e.g. hematite, magnetite, etc are oxides of iron. The fully oxidized remains of a scrapyard would form pretty much perfect iron ore. Our iron (and other metal) mining is not "using iron up", it's just bringing the iron closer to the surface and transforming it in ways that will be undone by millions of years. Fossil fuels are a different case, though.
    - scottie_m 9y ago
      The majority is hematite, but iron exposed to air will not form hematite, or even magnetite, but hydrated oxides. That iron will also be spread out over large areas in low concentrations, not richly concentrated ores of oxides. It would be economically and energetically unfeasible to gather hydrated oxides from rusted metal and then try to make workable iron from it. It’s certainly possible, but it would be a kind of insane process with low yields. The other problem is that you need to use coke as a reducing agent, so we’re back to fossile fuels.
      - FreeFull 9y ago
        Charcoal also work as a reducing agent. The problem with using charcoal is that you're going to be using up a lot of wood to make it.
- soneil 9y ago
PeterisP 9y ago
We're not consuming iron, tin or copper - all the iron, tin and copper that we've brought up from underground is still there. The only difference is that a future civilization might need to look for these metals by smelting rubbishdumpitis and cityruinitis scattered e.g. close to river deltas where our major population centers are located now instead of hematite, magnetite or limonite scattered according to long-term geological processes.

by soneil 9y ago

cc439 9y ago

The problem with that line of thinking is addresses in the article. The oldest large scale area of "ancient" crust on land is a mere 1.8 million years old (the Negev Desert). The entire surface of the earth is regenerated on a scale of tens of millions of years, any depletion of surface deposits which occured ~100 million years ago would have long since been hidden by the replenishment of new crust provided by plate tectonics.

soneil 9y ago
I don't believe it covers that at all. I believe their definition of crust there is a lot more superficial than it sounds like. eg, the Chicxulub (Yucutan) crater is 66 million years ago, and clearly hasn't been recycled else we wouldn't be looking at it. We have dinosaur fossils dating ~230-240 million years, so the crust clearly hasn't been recycled that thoroughly. Indeed, the entire Pangea theory would be invisible to us if the continents didn't remain 300+ million years later. (I'm not saying we should have a fossil record of 'the others', as the article says, there's a survivor bias in fossils. Just that the fossils we do have wouldn't exist if the crust has been geologically renewed in the last few millions of years.) They're talking about surface markers like roads and buildings. To replace a previous civilization's trashheaps with geological mineral seams, you'd need to pre-date Pangea.

BurningFrog 9y ago

Unless they shipped the metals off planet, that's not really an argument. If anything, an iron using civilization would have made iron more concentrated and easier to find.

scottie_m 9y ago
Aluminum sure, but iron rusts. In tens of millions of years you could have oxides of iron from a civilization, but no workable steel or iron. Aluminum might survive, gold and platinum would be fine, but not iron. It doesn’t matter though, we’d have gone through many cycles of subduction and renewal in such a long time, so we’d have new surface deposits. Coal and oil would even have started to form over such a long time scale.
- PeterisP 9y ago
  What do you mean by "workable steel or iron" ? We're not mining for steel, and it's not like iron age started with finding some magic store of "workable iron" instead of iron oxides - the surface iron and mined iron deposits e.g. hematite, magnetite, etc are oxides of iron. The fully oxidized remains of a scrapyard would form pretty much perfect iron ore. Our iron (and other metal) mining is not "using iron up", it's just bringing the iron closer to the surface and transforming it in ways that will be undone by millions of years. Fossil fuels are a different case, though.
  - scottie_m 9y ago
    The majority is hematite, but iron exposed to air will not form hematite, or even magnetite, but hydrated oxides. That iron will also be spread out over large areas in low concentrations, not richly concentrated ores of oxides. It would be economically and energetically unfeasible to gather hydrated oxides from rusted metal and then try to make workable iron from it. It’s certainly possible, but it would be a kind of insane process with low yields. The other problem is that you need to use coke as a reducing agent, so we’re back to fossile fuels.
    - FreeFull 9y ago
      Charcoal also work as a reducing agent. The problem with using charcoal is that you're going to be using up a lot of wood to make it.
soneil 9y ago

PeterisP 9y ago

We're not consuming iron, tin or copper - all the iron, tin and copper that we've brought up from underground is still there. The only difference is that a future civilization might need to look for these metals by smelting rubbishdumpitis and cityruinitis scattered e.g. close to river deltas where our major population centers are located now instead of hematite, magnetite or limonite scattered according to long-term geological processes.