Through the processes of weathering and the 'work' of microorganisms it takes millions of years to make substantial soil. 20% air, 20% water, 50% minerals and 10% microorganisms and plant matter, soils are the basis of all terrestrial life. A handful of healthy soil contains more microorganisms than the planet's entire human population.
More or less simultaneously, urban civilization grew out of the rich soil deposits of the Nile, the Tigris and Euphrates, the Indus and the Huang He rivers. Then, as today, the mismanagement of soil meant failed harvests, inciting socio-political tensions and ultimately the demise of whole cities, in some cases, entire cultures.
Only since refrigeration, high speed travel and 'the green revolution' of the 20th century has settlement become unhinged from close proximity to productive soil and a majority of the global population liberated from tillage. But the spectacular ability we now have to (almost) feed a world of seven billion, and probably over 10 billion by century's end is ultimately caught in a cycle of diminishing returns unless the world's soil is arable. 1
According to the United Nation's Food and Agriculture Organization (FAO), croplands in 2015 take up 15.3 million km2. In addition to this, pasture for animal grazing covers another 33.8 million km2; together a total foodscape of 49.1 million km2- 38 per cent of the earth's ice-free land. According to the 2015 Soil Atlas about 8.4 million hectares of productive land is lost each year due to erosion, salination, toxicity and urban development. 2 Additionally, high yields are only made possible through the liberal application of industrially manufactured fertilizers and pesticides, themselves drawn from limited resources which ultimately destroy the biodiversity in soils. Most problematic is that reactive nitrogen and phosphate run-off from industrialized agriculture causes extensive eutrophication of inland waterways and the proliferation of 'dead (hypoxic) zones' in the oceans.
Paradoxically, however, the application of industrially manufactured fertilizer has arguably saved considerable terrestrial habitat from clearance. Oliver Morton, author of The Planet Remade estimates that an additional agricultural landscape the size of Russia (17 million km2) would be needed to feed today's population if it wasn't for manufactured nitrogen as fertilizer. 3
1 United Nations, Department of Economic and Social Affairs, Population Division, World Population Prospects: The 2015 Revision, Key Findings and Advance Tables (2015). Available at https://esa.un.org/unpd/wpp/Publications/.
2 Christine Chemnitz & Jes Weigelt (eds), The Soil Atlas 2015 (Berlin & Potsdam: Heinrich Böil Foundation & Institute for Advanced Sustainability Studies, 2015). Available at http://globalsoilweek.org/wp-content/uploads/2014/12/soilatlas2015_web_141221.pdf.
3 Oliver Morton, The Planet Remade: How Geoengineering Could Change the World (Princeton University Press, 2015), 204.
Source: Land and Water Development Division, FAO, Rome, "Digital Soil Map of the World" (2007). Available at http://www.fao.org/geonetwork/srv/en/metadata.show?id=14116 (accessed June 14, 2015).
Critical Ecosystem Partnership Fund, "The Biodiversity Hotspots," http://www.cepf.net/resources/hotspots/pages/default.aspx (accessed July 1, 2014). Data made available under the Creative Commons BY-SA 4.0 License: https://creativecommons.org/licenses/by-sa/4.0/legalcode.