[dredmorbius]

And the concentration into BIFs, banded iron formations, was all but certainly the result of biological activity.

Our present technology based on iron and steel owes itself to early life on Earth, from 1.6 to as much as 4 billion years ago. As with petroleum and coal-bed formation, a process unlikely to repeat in Earth's future. Iron ores are abundant, but still a finite resource.

<https://en.wikipedia.org/wiki/Banded_iron_formation>

[jrussino]

Human civilization feels so much more fragile to me since I realized how much we owe our technological progress to the accumulated effects of biological processes over geological timescales. Fossil fuels seem like the most obvious part of this story. If we had to start over "from scratch", would it even be possible? Or have we already so thoroughly exhausted the low-hanging energy stores that a second "industrial revolution" would be effectively impossible if our present civilization collapsed deeply enough?

I wasn't aware that concentrated stores of iron are also an important part of this story!

[eru]

> Or have we already so thoroughly exhausted the low-hanging energy stores that a second "industrial revolution" would be effectively impossible if our present civilization collapsed deeply enough?

There's plenty of coal left, and we will likely never exploit it, because solar is getting so cheap.

Also, despite long prophecies, peak oil never arrived either. So it doesn't look like we are running out of that stuff.

[meindnoch]

>Iron ores are abundant, but still a finite resource.

The iron doesn't go anywhere (ok, except for the iron making up our space probes). It is infinitely recyclable.

[dredmorbius]

It doesn't concentrate itself, at scale.

That's what ores are. Ores are useful because they are concentrated, the result of some ore-formation or ore genesis process.

The "not going anywhere", after it's been dispersed throughout the lithosphere, is precisely the problem.

<https://en.wikipedia.org/wiki/Ore_genesis>

[meindnoch]

But scrap metal is still purer than any ore.

[dredmorbius]

And ferrous mineral recycling accounts for roughly 33% of present production (2018 data, most current available):

<https://www.epa.gov/facts-and-figures-about-materials-waste-...>

That's a loss of 2/3 of production to non-scrap effluvia on an annual basis. I'll let you work out the ultimate resource depletion cycle from that. Recycling is useful, but it's no magic bullet, and there are always losses.

The most heavily recycled metal in the US is lead, per USGS data and prior comments of mine, with recovery rates of about 75%, accounting for 40% of net production.

<https://news.ycombinator.com/item?id=20164506>

<https://news.ycombinator.com/item?id=26412585>

Source citation: "USGS 2020 Minerals Yearbook: Recycling — Metals"

<https://www.usgs.gov/centers/nmic/recycling-statistics-and-i...>

[potato3732842]

>That's a loss of 2/3 of production to non-scrap effluvia

Considering that the amount of stuff in our world made from steel at any one time is steadily increasing this makes sense.

>The most heavily recycled metal in the US is lead, per USGS data and prior comments of mine, with recovery rates of about 75%, accounting for 40% of net production.

There's little to no "post consumer pre-recycler" use for lead whereas every tom dick and harry can find a use for some old pipes or beams or whatever.

[meindnoch]

That just means it's currently more economical to mine iron ore than it is to mine landfills.

[eru]

And we are presumably still adding to the total stock of iron in human circulation.