Alejandro Zaera-Polo

The earth common addresses the organic resources which make up the biosphere. Earth processes in cities relate fundamentally to the synthesis and resilience of life—human and otherwise—within urban environments. Life on Earth would be impossible without incessant cycling of key elements that make up biomass. Three cycles – those of carbon, nitrogen and sulphur—are particularly noteworthy: carbon is, of course, the dominant constituent of all living matter (typically 45-50% of dry weight). These three cycles are remarkable because of their complexity, the importance of microbes in their functioning, and because the cycled elements are transported by both air and water away from their sources. How these cycles interact with urban cycles is the key to the perpetuation of non-human life in the city.

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1. Hermann Bothe, William Edward Newton, and Stuart Ferguson, eds., Biology of the Nitrogen Cycle (Amsterdam: Elsevier Science, 2006)
2. Steven B. Carroll and Steven D. Salt, Ecology for Gardeners (Portland, OR: Timber Press, 2004)
3. Smil, “Nitrogen Cycle and World Food Production.”
4. Ibid.
5. P.M. Vitousek, J. Aber, R.W. Howarth, G.E. Likens, P.A. Matson, D.W. Schindler, W.H. Schlesinger, and G.D. Tilman, “Human Alteration of the Global Nitrogen Cycle: Sources and Consequences,” Issues in Ecology 1(3) (1997): 1-17.
6. Smil writes: “Without the use of nitrogen fertilizers we could not secure enough food for the prevailing diets of nearly 45% of the world’s population, or roughly three billion people.” Smil, “Nitrogen Cycle and World Food Production.”