Natural capital.

In 1969, [engineer, architect, and futurist Buckminster] Fuller asked J. Fran├žois de Chadenedes, a petroleum geologist, to figure out what it cost Mother Nature to make one gallon of petroleum. The innovator instructed the geologist to include the cost of photosynthesis as well as the slow cooking by heat and pressure into crude over millions of years. De Chadenedes obliged, estimating the price at more than $1 million per gallon. (62)

From: Nikiforuk, Andrew. The Energy of Slaves: Oil and the New Servitude. Madeira Park, BC: Douglas & McIntyre, 2012. EPUB file.