[Retric]

There are two ways to look at this the way we do things now or the actual limits. For ideas based on now see: http://money.howstuffworks.com/question213.htm

For limits see some quick math, you can probably mine down about 20 miles without getting to fancy in 2512 esp relative to a space elevator. Texas is 20 miles * 268,800 sq miles = 10^16 cubic meters. Platinum has an average rarity ~5 millionth of a gram per kg. aka 5 parts per billion which works out to ~10,000,000 cubic meters in the top 20 miles of Texas granted your playing with density's etc but 10,000,000 tons is reasonable estimate compared to around ~100 tons mined each year. Now we might be better off mining asteroids than Texas, don't assuming we need to leave the planet any time soon.

PS: It may be a mainstay of sci-fi, but there is little actual evidence that asteroids are going to have particularly high levels of any of the really rare stuff. (other than H3)

[schiffern]

>PS: It may be a mainstay of sci-fi, but there is little actual evidence that asteroids are going to have particularly high levels of any of the really rare stuff. (other than H3)

Untrue. Iridium is the rarest element in the Earth's crust. The majority of the known deposites come from asteroids.

It's not just Iridium, either. Compare these two charts:

https://en.wikipedia.org/wiki/File:Elemental_abundances.svg and https://en.wikipedia.org/wiki/File:SolarSystemAbundances.png

Why are they so different? Basically all the heavy and iron-loving stuff sank.

https://en.wikipedia.org/wiki/Iron_catastrophe https://en.wikipedia.org/wiki/Planetary_differentiation

[kens]

I was puzzled by this, since obviously there are elements that are more rare than iridium, so I checked the original data source. They eliminate most radioactive elements which kind of makes sense. I was a bit surprised to learn that polonium and radium are less common in the crust than iridium. They also eliminate noble gases from the list, of which krypton, xenon, and radon turn out to be rarer in the crust than iridium. Also a couple sources have rhenium rarer than iridium.

(I'm not trying to be pedantic and start an argument, but just fill in some information in case anyone else wondered about this data.)

See http://en.wikipedia.org/wiki/Abundances_of_the_elements_(dat... and http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earths...

[rpm4321]

It seems like we are having two different arguments. My main point here has been that material scarcity will likely be a non-factor in the future. You seem to be in agreement with that point, but seem dead set against the practicality of space mining.

Throughout my comments I've maintained that molecular assemblers/disassemblers (and possibly VR) should drastically lessen the amount of materials we consume. I'm simply saying that if we do run into scarcity issues, worst case, space mining should be many, many orders of magnitude cheaper within this time span.

Right now the US goes to the expense of floating rare earth elements on freighters from halfway across the globe, simply because we don't want to deal with the pollution, real property rights, safety issues, regulatory issues, and eyesores resulting from US mining operations. With the expected reductions in cost to achieve orbit, in 2112 the asteroid belt could very easily be the new China.

Now you could argue that the same breakthroughs that allow cheaper space mining would allow us to cleanly and efficiently extract resources in greater number from the earth - "molecular mining", if you will. That may be the case, but it's really impossible to predict to that degree of specificity at this point in time. We're probably arguing over what in the future would be the equivalent of going to the Walmart down the block or the Target across town to get a package of batteries. It probably doesn't matter.

Besides, the amount of materials we need really depends on how ambitious humanity wants to get:

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