Bingowings said:

The solar system has thousands of years (probably millions of years) worth of mineral ores in it.

Even if you went wild with technology.

As I say in the time frame now given to us depletion makes no sense.

Maybe there was some accident mining asteroids or draining gas giants but regulation as a means to prevent corporate wars isn't 'random' it has historical precedent (East India Company anyone?).

I believe their looking for oil, specifically for manufacturing plastics, as in the future they use Mr Fusion or something. IIRC thats in the novelisation.

oh yeah, and Prometheus sucked royally.