"Systems may be open or closed in respect to a number of inputs and outputs. Three important classes are matter, energy, and information. The present world economy is open to all three. We can think of the world economy or "econosphere" as a subset of the "world set," ...the set of all objects, people, organizations [etc.] This total stock of capital is... an open system... it has inputs... being production which adds to the capital stock, [and] outputs being consumption which subtracts from it. ...[W]e see objects passing from the noneconomic into the economic in... production, and... products passing out of the economic set as their [monetary] value becomes zero. Thus we see the econosphere as a material process involving the discovery and mining of fossil fuels, ores, etc., and at the other end... effluents... are passed out into noneconomic reservoirs—[e.g.,] the atmosphere and the oceans—which... do not enter into the exchange system."