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.