Energy and mass are conserved in closed systems. Looking at our universe, the solar system, the earth and using the concept of closed systems we find the following. Since the earth can be looked upon as a “closed system” then we can conclude that what we consume in terms of any fossil natural resources, i.e. being mined and used, is irreversible and can not be brought back as they were before. The same can be also said about natural minerals. Furthermore, all irreversable processes (mining and associated production to other forms, e.g. energy and industrial products) generally give rise to irreversible hazardous products in form of waste and pollution that impacts negatively on the functioning of natural systems. These natural systems, e.g. aquatic systems and land-water resources are generally expected to go out of order and to suffer from “malfunctioning”. In this context the earth’s natural resources can be generally classified into four main categories: 

(1) Mined and used irreversibly with major and remarkable large-scale and long-term damaging effects and negative environmental impacts 

(2) Mined and can be used reversibly but with high economic costs and major side-effects and negative environmental impacts

(3) Mined and can be used reversibly with minor economic costs and limited negative environmental impacts

(4) used and reused reversibly with limited environmental impacts