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Historically , this was identified as the metabolic rift by Karl Marx , who identified the unequal exchange rate between energy and nutrients flowing from rural areas to feed urban cities that create effluent wastes degrading the planet 's ecological capital , such as loss in soil nutrient production .
 Karl Marx
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
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Answer:
 Karl Marx