(urth) "been teaching literature for over 35 years"

[David Stockhoff]

On 9/8/2013 6:07 PM, Jeff Wilson wrote:
> Back in ~1980, I believe the isotopic decay source was the only one
> generally recognized, and it's possible that the metal depletion mentioned
> in the Book would be of*radioactive*  metals, powering the great ships and
> robots aboard them. This explains a possible reason for there to be still
> funeral bronzes and moveable type in a metal poor world, and of course
> isotopes sent into space can't keep the crust lubricated.

How far down would humans have to strip the mantle (using robots, of 
course) to mess with tectonics? Wouldn't the entire planetary surface 
have to be mined? or just where plates meet?