I have always been sceptical about claims that overpopulation and economic growth are causing us to run out of resources. In fact, for the past several hundred years, improvements in technology have permitted us to exploit more and more of the various essential resources that we need, and bring the cost down and down.
There was a famous wager between economist Prof. Julian Simon and author Dr. Paul Ehrlich, in which Simon claimed that resources become cheaper due to greater availability, and Ehrlich claimed we were running out, which would result in higher prices.. Simon won.
http://en.wikipedia.org/wiki/Simon-Ehrlich_wager
Each time we use up a type of resource, we develop other techniques to extract other sources. For example : gold is very scarce, but it is known that a form of gold (called microcrystalline) in certain common minerals holds lots of gold (relatively speaking).
http://www.geologynet.com/gpros.htm
We cannot extract microcrystalline gold at this point in time, but when we develop the technology, it will dramatically increase the quantity of known gold reserves.
In Iceland, there is a project to drill down to molten magma, which can be tapped for energy.
http://en.wikipedia.org/wiki/Iceland...illing_Project
However, one of the possible side benefits of this project is to use that magma as a source for mineral extraction. Probably some years in the future, but a real possibility. According to
New Scientist (7 November 2009, page 18) the drillers have already struck molten magma at 2104 metres depth. In 2005, a drilling project in Hawaii also struck magma.
I could envisage a time in the future when pumping magma and using it as a source of both energy and minerals would be commonplace.
The point of all this is that resources are far more available than most alarmist would-be prophets are prepared to accept. As humanity develops better technology, we tap into more and more sources of vital resources.
The Earth weighs 6,000,000,000,000,000,000,000 tonnes. That includes one hell of a lot of resources!