Earth as a System: Energy, Matter and Life - Describe water, carbon, nitrogen, and oxygen cycles and human impact on Earth systems

The Earth system is composed of four interacting spheres: the Lithosphere (land), Hydrosphere (water), Atmosphere (air), and Biosphere (life).

The Water Cycle involves the continuous movement of water through processes like Evaporation, Transpiration (from plants), Condensation (forming clouds), and Precipitation ($Rain/Snow$).

The Carbon Cycle maintains the balance of carbon in the atmosphere. Carbon enters the biotic world via Photosynthesis ($6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$) and returns via Respiration, Decomposition, and Combustion.

The Nitrogen Cycle is crucial because $N_2$ gas makes up $78\%$ of the atmosphere but cannot be used directly by most organisms. It must be 'fixed' into nitrates ($NO_3^-$) or ammonium ($NH_4^+$) by bacteria like Rhizobium or lightning.

The Nitrogen Cycle steps include: Nitrogen Fixation $\rightarrow$ Nitrification $\rightarrow$ Assimilation $\rightarrow$ Ammonification $\rightarrow$ Denitrification.

The Oxygen Cycle is driven by Photosynthesis (which releases $O_2$) and Respiration/Combustion (which consume $O_2$).

Human Impact: Industrialization and deforestation increase $CO_2$ levels, leading to the Greenhouse Effect and Global Warming. Excessive use of fertilizers leads to Eutrophication in water bodies.

The Ozone Layer ($O_3$) in the stratosphere protects Earth from harmful UV radiation, but is being depleted by Chlorofluorocarbons (CFCs).