90. Carbon Cycle & Water Cycle

Life on Earth relies on the constant recycling of elements and molecules. Atoms are used repeatedly across millions of years, moving through the atmosphere, oceans, and living organisms.

1. The Water Cycle

The water cycle describes how water moves between the Earth's surface and the atmosphere.

• Evaporation & Transpiration: Energy from the sun heats water in oceans, lakes, and soil, causing it to evaporate into water vapor. Plants also release water vapor through their leaves in a process called transpiration.

• Condensation: As water vapor rises and cools, it condenses to form clouds.

• Precipitation: Water falls back to the Earth's surface as rain, snow, or hail.

• Collection: The water runs into rivers, seeps into the soil, or is taken up by plants, eventually returning to the start of the cycle.

2. The Carbon Cycle

Carbon is a fundamental building block of life. The cycle moves carbon between the atmosphere, living things, and the ground.

Key Carbon Stores:

• Atmosphere: As carbon dioxide (CO₂).

• Plants: Locked in biological molecules like glucose.

• Animals: Stored in tissues after consuming plants or other animals.

• Soil: Contained within microorganisms and decaying matter.

• Fossil Fuels: Stored underground (coal, oil, gas).

Key Processes:

• Photosynthesis: Green plants and algae remove CO₂ from the atmosphere to make glucose. This is the only process that removes carbon from the air.

• Respiration: Plants, animals, and microorganisms release CO₂ back into the atmosphere as a byproduct of releasing energy.

• Decomposition: When organisms die, they are broken down by decomposers (bacteria and fungi). These decomposers respire, releasing carbon back into the air.

• Combustion: Burning fossil fuels or wood releases stored carbon back into the atmosphere as CO₂.

3. Decomposition Conditions

Decomposition happens most effectively when microorganisms have the right environment:

• Oxygen: Required for aerobic respiration.

• Moisture: Prevents the microorganisms from drying out.

• Warmth: Increases the rate of chemical reactions within the decomposers.

If organisms die in anaerobic conditions (no oxygen), they do not decay fully and may eventually form fossil fuels over millions of years.

Summary Table: Carbon Cycle Processes