D.2] Important Geographical Cycles

1. Water Cycle (Hydrologic Cycle)

Definition

The continuous movement of water on, above, and below the surface of the Earth.

Key Processes

• Evaporation: Water changes from liquid to vapor due to solar heat.
• Condensation: Water vapor cools and forms clouds.
• Precipitation: Water falls as rain, snow, sleet, or hail.
• Runoff: Water flows over the land surface into rivers, lakes, and oceans.
• Infiltration: Water seeps into the ground and replenishes groundwater.
• Transpiration: Water is released from plants into the atmosphere.

Key Facts (SSC, RRB)

• Important Date: The water cycle has been active since the formation of Earth (around 4.5 billion years ago).
• Important Term: Hydrological cycle.
• Important Example: The monsoon cycle in India is a major example of the water cycle.

Table: Water Cycle Stages

2. Carbon Cycle

Definition

The movement of carbon through the Earth’s atmosphere, oceans, soil, and living organisms.

Key Processes

• Photosynthesis: Plants absorb CO₂ and convert it into organic matter.
• Respiration: Organisms release CO₂ back into the atmosphere.
• Decomposition: Dead organic matter is broken down, releasing CO₂.
• Combustion: Burning of fossil fuels releases CO₂.
• Ocean Absorption: Oceans absorb and store large amounts of CO₂.
• Sedimentation: Carbon is stored in sedimentary rocks over long periods.

Key Facts (SSC, RRB)

• Important Date: The carbon cycle has existed for about 4.5 billion years.
• Important Term: Carbon sequestration.
• Important Example: The Great Barrier Reef is a significant carbon sink.

Table: Carbon Cycle Components

3. Nitrogen Cycle

Definition

The movement of nitrogen through the environment, including the atmosphere, soil, and living organisms.

Key Processes

• Nitrogen Fixation: Conversion of atmospheric nitrogen (N₂) into usable forms (e.g., ammonia) by bacteria.
• Nitrification: Conversion of ammonia to nitrites and nitrates by bacteria.
• Assimilation: Plants absorb nitrates and convert them into proteins.
• Ammonification: Decomposition of organic nitrogen into ammonia.
• Denitrification: Conversion of nitrates back into nitrogen gas by bacteria, returning it to the atmosphere.

Key Facts (SSC, RRB)

• Important Date: The nitrogen cycle has existed for about 4.5 billion years.
• Important Term: Nitrogen fixation, denitrification.
• Important Example: Leguminous plants (e.g., peas, beans) are key in nitrogen fixation.

Table: Nitrogen Cycle Stages

Differences Between Cycles