The carbon cycle describes how carbon moves between atmosphere, biosphere, oceans, and geosphere. It is central to both life and climate regulation.
Atmospheric carbon dioxide (CO₂) is fixed by plants during photosynthesis. Plants convert CO₂ into sugars, which are used for growth or exuded into the soil to feed microbes. Animals, including humans, consume plants and release CO₂ back through respiration. When plants or animals die, decomposers (bacteria, fungi) break down organic matter, releasing CO₂ or methane (CH₄). This is the biological carbon cycle, which operates on timescales of days to centuries.
Carbon also moves into long-term storage. In soils, organic carbon can be stabilized for decades to millennia via microbial processing, aggregation, or chemical bonding to minerals. In oceans, CO₂ dissolves and is fixed by phytoplankton, some of which sink to the deep sea as sediment. Over geological timescales, carbon is stored in fossil fuels and carbonate rocks. Volcanic activity and human fossil fuel use return this carbon to the atmosphere, influencing climate. The importance of soils is often underappreciated: they store more carbon than all vegetation and the atmosphere combined. Disturbance, tillage, and land degradation have historically released large amounts of carbon from soils. The carbon cycle is therefore both an ecological foundation and a climate lever. In regenerative agriculture the overall aim is to increase carbon storage in the soil which contributes to soil fertility, water retention, and global climate mitigation simultaneously. Understanding where carbon resides, how it moves, and how to stabilize it is key to designing resilient agroecosystems.
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