exergy inputs to describe the transition from biological material to fossil fuels during millions of years in the Earth's crust, and solar radiation exergy inputs to describe the material's history before then when it was part of the biosphere. This would need to be carried out mathematically backwards through time, to a presumed era when the oil and coal could be assumed to be receiving the same exergy inputs from these sources. A speculation about a past environment is different from assigning a reference state with respect to known environments today. Reasonable guesses about real ancient environments may be made, but they are untestable guesses, and so some regard this application as pseudoscience or pseudo-engineering. The field describes this accumulated exergy in a natural resource over time as embodied energy with units of the "embodied joule" or "emjoule". The important application of this research is to address sustainability issues in a quantitative fashion through a sustainability measurement: Does the human production of an economic good deplete the exergy of Earth's natural resources more quickly than those resources are able to receive exergy? If so, how does this compare to the depletion caused by producing the same good (or a different one) using a different set of natural resources? Assigning one thermodynamically obtained value to an economic good A technique proposed by systems ecologists is to consolidate the three exergy inputs described in the last section into the single exergy input of solar radiation, and to express the total input of exergy into an economic good as a solar embodied joule or sej. (See Emergy) Exergy inputs from solar, tidal, and geothermal forces all at one time had their origins at the beginning of the solar system under conditions which could be chosen as an initial reference state, and other speculative reference states could in theory be traced back to that time. With this tool we would be able to answer: What fraction of the total human depletion of the Earth's exergy is caused by the production of a particular economic good? What fraction of the total human and non-human depletion of the Earth's exergy is caused by the production of a particular economic good? No additional thermodynamic laws are required for this idea, and the principles of energetics may confuse many issues for those outside the field. The combination of untestable hypotheses, unfamiliar jargon that contradicts accepted jargon, intense advocacy