It is extremely difficult to get raw materials from outer space. Functionally equivalent renewable substitutes could be found for nonrenewable resources that are in limited supply. It will be a few hundred years before the Earth is depleted of certain nonrenewable resources that are in limited supply. Some economically useful resources are renewable.
Many economically useful raw materials are nonrenewable and in limited supply on Earth. Ttherefore, unless those materials can be obtained somewhere other than Earth, people will eventually be unable to accomplish what they now accomplish using those materials.
Which one of the following, if true, most seriously weakens the argument?