Prior to the evolution and arrival of humans on Earth, changes in the Earth's atmosphere, lithosphere, hydrosphere, cryosphere, and biosphere had been occurring for billions of years. Global environmental change is nothing new, but what is new are the rates of change that the Earth systems are currently experiencing because of human activities. The rate of change in these systems since the arrival of the human species is more rapid than any other time in history, with the possible few exceptions of massive extinctions that may have been caused by large meteorite impacts. Many, but not necessarily all, of these more recent changes are related to humans and their natural resource needs and requirements. The retrieval, production, distribution, consumption, and disposal of these natural resources along with the continued growth and distribution of the human population on the planet are resulting in drastic changes to the Earth and its environmental ecosystems.
Natural resources are the many different forms of available energy, minerals, and organic matter on Earth that humans can exploit (e.g., iron, coal, wood, oil, etc.). Noncommercial items (e.g., clean air, aesthetic value of landscape, noncommercial organisms that make up an ecosystem) do not necessarily provide monetary gain and ordinarily are not referred to as natural resources. The natural resources that humans are dependent upon may be renewable or nonrenewable. Examples of renewable resources include forests, agricultural crops, and certain types of energy such as wind, solar, tidal, ocean thermal, geothermal, and biomass to name a few. All these resources can be replaced on a short-term basis although that does not necessarily always happen (e.g., deforestation). Other commercial resources such as oil, gas, coal, and minerals are nonrenewable. They are resources depleted by excessive use, because of loss through non-recycling methods of disposal, or because there are fixed supplies of the substance on Earth which take millions of years to replenish by natural processes.