Work based upon benefit transfer , compiled by ecologist\/planner Robert Costanza in the 1990s , has claimed that even just considering the most basic seventeen of these services , the combined value of the ecosystems of the Earth was worth more ( US$ 33T ) each year ; more than the whole human exchange economy ( US$ 25T ) at that time ( 1995 ) , which is rather strange for an exchange value .
Studies compiled by Robert Costanza in the 1990s argued strongly that even just considering the most basic seventeen of these services , the combined value of the ecosystems of the earth was worth more ( US$ 33T ) each year than the whole human exchange economy ( US$ 25T ) at that time ( 1995 ) .