For that reason, your mother is perhaps a more environmentally conscious person than a lot of us. The point never is whether we will run out, because that is a certainty; the point always is when and how long. With better technology and prudent use of natural resources we can certain make it last through my lifetime (I am 49), perhaps to some extent my daughters life-time; but that is about it. At that point in time we would have consumed most of the natural resources of this planet, and we have to look elsewhere. It is highly likely we won't be able to take most of the population, in theory most will perish long before. If we are lucky as a species, there could be a potential future where a very small group of lucky species can leave this planet. However, I see no reason to hope or celebrate that outcome, even if that is a distant possibility.