Carbon Cycle

Biogeochemical Cycles: The flow of molecules through different living and non-living levels of the Earth; here, the CARBON CYCLE:


•Atmosphere:  CO2 molecules in the air
•Biosphere: Photosynthesis by plants, algae & bacteria absorbs CO2 and makes glucose; Respiration by all living things on land and in the water releases CO2
•Geosphere: Carbon stored in hydrocarbons (H-C in coal, oil, natural gas) or limestone (calcium carbonate, CaCO3, made by shells of ocean life)

Short-term cycle:
-The amount of CO2 in the air remains about constant year-to-year because:

•The amount absorbed for photosynthesis = the amount released by cellular respiration, decomposition, forest fires, etc.

Long-term cycle:
-Over a period of millions of years, the CO2 content fluctuates some but stays about the same

•Carbon from dead plants and animals slowly accumulates and is stored for long periods of time in rock layers as fossil fuels or limestone
•Volcanoes, a geologic process, burn rocks and release CO2 and other gases into the atmosphere

Human Impact on the Carbon Cycle

•When we drive cars or burn coal, oil, or gas for energy or heat, the process releases CO2 and H2O, just like aerobic respiration
•Burning fossil fuels rapidly alters the long-term carbon cycle by adding lots of carbon to the atmosphere quickly
•CO2 acts as a “greenhouse gas,” trapping heat that would otherwise escape and warming the planet

Historical levels of CO2:           300 ppm
Current levels of CO2:              380 ppm
Future levels of CO2 by 2100:  540-970 ppm, estimated