Carbon Cycle

The carbon cycle is the circulation of carbon atoms through both living (biotic) and nonliving (abiotic) components of the Earth’s various systems, including the atmosphere, biosphere, hydrosphere, and lithosphere. Carbon cycles rapidly between these spheres through key processes like photosynthesis, respiration, decomposition, and combustion. Human activities are also influencing the carbon cycle, mainly through deforestation and burning fossil fuels.

Key Processes and Elements

• Atmospheric CO2: Carbon dioxide in the atmosphere is a crucial starting point. It’s involved in several exchange processes.
• Photosynthesis in Plants: Plants absorb atmospheric CO2 and convert it into organic matter through photosynthesis.
• Respiration: Both plants and animals release CO2 back into the atmosphere through respiration.
• Consumption: Animals obtain carbon by consuming plants.
• Decomposition: When plants and animals die, their decomposition releases carbon into the soil and, eventually, back into the atmosphere.
• Ocean Absorption: Oceans absorb a significant amount of CO2 from the atmosphere.
• Marine Life: Within oceans, marine organisms use carbon for photosynthesis and contribute to the carbon cycle through their life processes.
• Marine Sediments: When marine organisms die, their remains contribute to marine sediments, which can eventually form fossil fuels.
• Fossil Fuels: Geological processes convert organic matter in sediments into fossil fuels like coal and oil, which contain high levels of carbon.
• Combustion of Fossil Fuels: Burning fossil fuels releases stored carbon back into the atmosphere as CO2.
• Formation of Carbonates: In oceans, chemical processes convert carbon into carbonates, which can also end up in sediments.

Long-Term Carbon Storage

While part of the biotic carbon cycle is rapid, carbon can also be stored for very long periods in fossil fuels and sedimentary rock. Fossil fuels like coal and oil contain carbon from once-living organisms and form over millions of years. Calcium carbonate shells from dead marine organisms can form limestone and other carbonate sedimentary rock, storing carbon until geological processes expose them.

Example: Carbon stored in ancient plant matter turned into coal deposits over hundreds of millions of years. This carbon stays locked away until the coal is burned for fuel, releasing the carbon back into the carbon cycle.

Human Influences on the Carbon Cycle

Human activities like deforestation and the burning of fossil fuels release vast quantities of previously stored carbon into the atmosphere in the form of carbon dioxide. Reducing vegetation also limits the Earth’s capacity to absorb and process CO2 through photosynthesis. If too much carbon dioxide enters and remains in the atmosphere, it could contribute to global climate change.

Example: The cutting and burning of rainforests releases carbon stored in trees back into the atmosphere. It also reduces the number of trees available to absorb CO2 through photosynthesis and respiration. This shifts the balance of the carbon cycle.