Resources are finite, they will eventually run out.
All resources are finite except those that nature provides as part of its own sustainable cycle, everything else sooner or later comes to an end and the more of nature that we destroy the more we will have to provide ourselves. Resource availability has five stages: we don't have it because we can't get at it, we have access to it and we're actively getting it, getting it has become too expensive (you end up alternating between this one and the previous one for a while), we have to get it from our previous waste material because the original sources have all run out and finally we no longer have it in a form that we can get at it because it has become too dispersed.
Every resource that came as a gift with the 'bare' planet (before life began and exposed by various tectonic processes) follows these stages. So the more of nature we leave in one piece and the more we work in a sustainable manner (maximize recycling, for instance) the longer humanity will survive in a recognizable form. The only other way that I can think of is to go off-planet.