Carbon: The Building Block of Life on Earth

Carbon is a fundamental element that forms the basis of all life on Earth. It is found in the atmosphere, oceans, soils, rocks, and all living organisms. Because of its ability to form complex molecules, carbon supports biological processes, regulates the Earth’s climate, and provides vital resources for human use.

1. The Role of Carbon in Supporting Life

1.1 The chemical foundation of life

• Carbon atoms can bond with many other elements (especially hydrogen, oxygen, and nitrogen), forming complex organic molecules such as carbohydrates, proteins, and fats.
• These molecules store energy and provide the structural framework for all living organisms.

1.2 The carbon cycle

• Carbon moves continuously between the atmosphere, biosphere, hydrosphere, and lithosphere through a series of natural processes.
• Key processes include photosynthesis, respiration, decomposition, weathering, and combustion.
• This global cycle ensures a balance between carbon stores and fluxes, maintaining the conditions required for life.

1.3 Energy transfer

• Carbon compounds store chemical energy. When they are oxidised through respiration or combustion, energy is released.
• This energy drives biological and physical systems — from plant growth to atmospheric circulation.

1.4 Climate regulation

• Carbon dioxide (CO₂) and methane (CH₄) are key greenhouse gases that help regulate global temperatures by trapping outgoing longwave radiation.
• Without them, the Earth would be around 33°C cooler and unable to support complex life.

2. Carbon in the Natural World

2.1 In the atmosphere

• Carbon exists mainly as carbon dioxide (CO₂) and methane (CH₄).
• These gases influence the planet’s energy balance and climate.

2.2 In the biosphere

• Plants use atmospheric CO₂ in photosynthesis to produce organic matter.
• Carbon is passed through food chains as animals feed on plants and one another.
• When organisms die, decomposers return carbon to the atmosphere and soil.

2.3 In the hydrosphere

• Oceans store about 50 times more carbon than the atmosphere.
• Carbon enters through diffusion and is stored as dissolved CO₂, carbonates, and marine biomass.
• Marine organisms such as phytoplankton play a key role in sequestering carbon through the biological pump.

2.4 In the lithosphere

• The largest store of carbon is in sedimentary rocks, formed over millions of years.
• Fossil fuels (coal, oil, gas) are concentrated geological carbon stores, formed from the remains of ancient plants and marine organisms.

3. The Importance of Carbon for Humans

3.1 Energy resources

• Fossil fuels provide around 80% of global primary energy.
• Combustion releases carbon dioxide, contributing to the enhanced greenhouse effect and climate change.

3.2 Industrial materials

• Carbon-based materials, such as plastics, asphalt, and synthetic fibres, are essential for construction, transport, and manufacturing.
• Carbon compounds are used in pharmaceuticals and agriculture (e.g. fertilisers and pesticides).

3.3 Food and agriculture

• Carbon compounds form the basis of carbohydrates, fats, and proteins — the essential nutrients in all food chains.
• Soil organic carbon improves fertility, structure, and water retention, supporting global food production.

3.4 Economic importance

• The exploitation of carbon-rich fossil fuels has underpinned industrialisation and global economic growth.
• The transition to low-carbon economies is now central to sustainable development.

4. Balancing Carbon in the Earth System

• Carbon sequestration: The capture and long-term storage of carbon in forests, soils, and oceans helps regulate atmospheric CO₂.
• Feedback mechanisms: Warming can release more carbon (e.g. from melting permafrost), amplifying climate change.
• Human influence: Deforestation, burning fossil fuels, and land-use change have altered the natural carbon balance.