Ugo Bardi talks about his new book, Extracted. He makes a some key points about depletion that seem to remain misunderstood no matter how many times they are explained – resource depletion is not about running out of supplies, but about diminishing economic returns. Eventually, it is simply so expensive to get minerals out of the ground that they are no longer accessible to everyday consumers.
On a related note, this principle of diminishing economic returns is why the boom in unconventional oil is entirely consistent with the peak oil argument.
The Earthbound Report 