Last reviewed 4 Nov 2026 · 2 min read
1. Types of cycles
| Type | Reservoir | Examples |
|---|---|---|
| Gaseous cycles | Atmosphere / oceans | Carbon, nitrogen, oxygen, water |
| Sedimentary cycles | Earth's crust (rocks, soil) | Phosphorus, sulphur, calcium |
Gaseous cycles recover faster from disturbance; sedimentary cycles are slow and can be locked away for long periods.
2. Water (hydrological) cycle
- Evaporation (oceans), transpiration (plants) → condensation → precipitation → infiltration, runoff, groundwater flow → back to the sea.
- Driven by solar energy and gravity; about 97% of Earth's water is in the oceans.
3. Carbon cycle
| Process | Effect |
|---|---|
| Photosynthesis | Removes CO₂ from the air into plants |
| Respiration and decomposition | Return CO₂ |
| Combustion of fossil fuels and biomass | Adds CO₂ — main human impact |
| Ocean exchange | Oceans dissolve CO₂ (carbonate, bicarbonate); a major sink |
| Sedimentation | Carbon locked in limestone and fossil fuels over geological time |
- Human impact: rising atmospheric CO₂ → global warming and ocean acidification; deforestation removes a sink.