Dr P. Buringh (Agricultural University of the Netherlands, Wageningen, The Netherlands) (1984): “The loss of organic matter from soil is mainly the result of the clearing of forests for grassland or cropland. On the basis of the assumptions outlined here, the annual loss of organic carbon from the world's soils is between 2.5x 1015g [2.5 GtC] and 7.4x 1015g, [7.4 GtC] with 4.6x 1015g [4.6 GtC] being considered a realistic estimate. These amounts are 0.2, 0.5 and 0.3 percent of the total organic carbon (1477x 1015g [1477 GtC] ) currently estimated to exist in the world's soils. Since the total organic carbon in soil in prehistoric times has been estimated as 2014x 1015g [2014 GtC] , the loss since then has been 537x 1015g [537 GtC] , or 27 percent of the amount present prior to the spread of civilization in the last two millennia” (P. Buringh, “Organic Carbon in Soils of the World”, Chapter 3 in G.M. Woodwell , editor, “The Role of Terrestrial Vegetation in the Global Carbon Cycle: Measurement by Remote Sensing”, John Wiley, 1984: https://dge.carnegiescience.edu/SCOPE/SCOPE_23/SCOPE_23_3.1_chapter3_91-109.pdf ).