The Carbon Cycle and Our Spheres

Lesson: The Carbon Cycle

 

Objective:
Students will learn about the carbon cycle, understand its key processes, and see how carbon moves between the Earth's spheres (hydrosphere, atmosphere, geosphere, and biosphere).

 

Section 1: Important Definitions

The carbon cycle describes how carbon is exchanged between Earth's different spheres. Carbon is a critical element for life, and it moves through the atmosphere, oceans, land, and living organisms in a continuous cycle.

Key Terms:

1. Carbon:

   • A chemical element that is the basis of all life. It exists in various forms, including carbon dioxide (CO₂), methane (CH₄), and in organic compounds like carbohydrates, proteins, and fats.

2. Atmosphere:

   • The layer of gases surrounding Earth. Carbon in the atmosphere is primarily found in the form of carbon dioxide (CO₂), which plants and other photosynthetic organisms use to create food.

3. Biosphere:

   • The sphere that includes all living organisms. Organisms take in carbon through respiration, photosynthesis, and other biological processes. Plants store carbon, and animals release it through breathing and digestion.

4. Hydrosphere:

   • The water component of Earth, including oceans, rivers, lakes, and groundwater. The oceans play a key role in storing and exchanging carbon, absorbing large amounts of CO₂ from the atmosphere.

5. Geosphere:

   • The solid Earth, including the crust, mantle, and core. Carbon is stored in rocks, fossil fuels, and soils. Geological processes like volcanic eruptions and the weathering of rocks release carbon into the atmosphere.

 

Section 2: The Stages of the Carbon Cycle

The carbon cycle is a series of processes that move carbon through the Earth’s spheres. Let’s break down each part of the cycle:

1. Photosynthesis (Biosphere → Atmosphere)

   • Plants and algae absorb carbon dioxide (CO₂) from the atmosphere and convert it into glucose (C₆H₁₂O₆) using sunlight.

   • This process stores carbon in plant tissues and creates oxygen as a byproduct.

   • Equation:  6CO2+6H2O+light→C6H12O6+6O2

2. Respiration (Biosphere → Atmosphere)

   • Animals, plants, and microorganisms release carbon back into the atmosphere by breaking down glucose (or other organic carbon compounds) to produce energy (ATP).

   • This releases carbon dioxide (CO₂) as a waste product

   • Equation:  C6H12O6+6O2→6CO2+6H2O+energy

3. Decomposition (Biosphere → Geosphere)

   • When plants and animals die, decomposers (fungi, bacteria) break down their remains, releasing carbon into the soil and returning it to the geosphere as organic material or as carbon dioxide.

4. Fossilization (Biosphere → Geosphere)

   • In rare cases, carbon from organisms gets trapped in sedimentary layers, forming fossil fuels like coal, oil, and natural gas over millions of years.

5. Combustion (Biosphere → Atmosphere)

   • When fossil fuels are burned for energy, carbon stored in those fuels is released into the atmosphere as carbon dioxide.

6. Ocean Uptake (Hydrosphere → Atmosphere)

   • The oceans absorb a significant amount of carbon dioxide from the atmosphere. Some of this carbon is used by marine plants (phytoplankton) in photosynthesis.

   • Oceans also store carbon in the form of dissolved inorganic carbon, and this carbon can be released back into the atmosphere over time.

7. Volcanic Activity (Geosphere → Atmosphere)

   • Carbon stored in Earth's crust is released into the atmosphere during volcanic eruptions. This carbon is primarily in the form of carbon dioxide (CO₂).

8. Weathering (Geosphere → Hydrosphere and Atmosphere)

   • The slow breakdown of rocks on Earth's surface releases carbon into the environment. For example, rain reacts with certain rocks (like limestone) and releases carbon dioxide into the water, which can be carried to the oceans.

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