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Unlock This CourseThe carbon cycle is one of nature's most important recycling systems. Carbon is the building block of all living things - it's in your body, in plants, in the air you breathe and even in rocks. This amazing element constantly moves around our planet in a never-ending cycle that has been happening for billions of years.
Think of carbon like money in the world's economy - it's always moving from one place to another, but the total amount stays roughly the same. Sometimes it's stored in one place for a long time (like in rocks or deep ocean water) and sometimes it moves quickly (like when you breathe out carbon dioxide).
Key Definitions:
Carbon is special because it can form four bonds with other atoms, making it perfect for building complex molecules like proteins, fats and DNA. Without carbon, life as we know it couldn't exist. Every living thing on Earth is made up of carbon-based molecules, which is why we're called "carbon-based life forms".
Carbon doesn't stay in one place - it's constantly moving between four main reservoirs on our planet. Each reservoir stores different amounts of carbon and releases it at different rates.
Contains carbon as CO₂ gas. Though it's the smallest reservoir, it's crucial because it directly affects climate. Currently about 0.04% of the atmosphere is CO₂.
The largest active carbon reservoir. Carbon dissolves in seawater and is used by marine plants and animals. Cold water holds more CO₂ than warm water.
Includes all plants, animals, soil and dead organic matter. Forests are particularly important carbon stores, holding carbon in wood and soil.
Carbon moves between these reservoirs through various processes, some fast and some incredibly slow. Understanding these processes helps us see how the carbon cycle works as a whole system.
Photosynthesis: Plants absorb CO₂ from the air and convert it into glucose. This happens during daylight hours when plants have energy from sunlight. A large oak tree can absorb about 22kg of CO₂ per year!
Respiration: All living things (including plants) break down glucose for energy, releasing CO₂ back to the atmosphere. This happens 24/7 in all living cells.
Ocean-atmosphere exchange: CO₂ constantly dissolves into ocean water and is released back to the atmosphere. Rough seas and wind increase this exchange.
These two processes are like opposite sides of the same coin - they balance each other out in healthy ecosystems. During the day, plants photosynthesise more than they respire, so they're net absorbers of CO₂. At night, they only respire, so they release CO₂.
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
This means: Carbon dioxide + Water + Light energy makes Glucose + Oxygen
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
This means: Glucose + Oxygen makes Carbon dioxide + Water + Energy
Some carbon processes take thousands or millions of years. These slow processes help regulate Earth's climate over long periods.
When rainwater (which contains dissolved CO₂) hits rocks, it slowly dissolves them in a process called chemical weathering. This removes CO₂ from the atmosphere very slowly - it can take thousands of years. The dissolved carbon eventually ends up in the ocean, where it might form limestone on the sea floor. This limestone can store carbon for millions of years until geological processes bring it back to the surface.
For thousands of years, the carbon cycle was in balance - the amount of CO₂ going into the atmosphere roughly equalled the amount being removed. However, human activities since the Industrial Revolution have dramatically changed this balance.
Coal, oil and gas are ancient carbon stores. When we burn them for energy, we release CO₂ that was locked away for millions of years, adding extra carbon to the atmosphere.
Cutting down forests removes important carbon stores and reduces the Earth's ability to absorb CO₂ through photosynthesis. Trees that took decades to grow can be cut down in minutes.
Making cement, steel and other materials releases CO₂. Even some farming practices, like rice cultivation, produce greenhouse gases that affect the carbon cycle.
When we add more CO₂ to the atmosphere than natural processes can remove, several things happen that affect the whole planet.
CO₂ is a greenhouse gas - it traps heat in Earth's atmosphere. More CO₂ means more heat gets trapped, leading to global warming. This affects weather patterns, sea levels and ecosystems worldwide. The concentration of CO₂ in the atmosphere has increased by over 40% since pre-industrial times.
As oceans absorb more CO₂ from the atmosphere, they become more acidic. This makes it harder for sea creatures like corals and shellfish to build their shells and skeletons, affecting entire marine ecosystems.
Despite human interference, nature has some amazing ways to absorb and store carbon. Understanding these natural solutions helps us work with the carbon cycle rather than against it.
Trees are excellent carbon storage systems. They absorb CO₂ as they grow and store carbon in their wood. Old-growth forests store more carbon than young forests.
Healthy soil contains lots of organic matter from dead plants and animals. This soil carbon can stay locked up for decades if the soil isn't disturbed.
Marshes, swamps and peatlands are incredibly efficient at storing carbon. They can store more carbon per hectare than forests!
Peatlands cover only 3% of Earth's land surface but store about 30% of all soil carbon. In waterlogged conditions, dead plant material doesn't fully decompose, so carbon gets locked away for thousands of years. However, when peatlands are drained or burned, they release massive amounts of CO₂ - sometimes more than entire countries produce from fossil fuels!
Understanding the carbon cycle helps us make better decisions about how to manage our planet's resources. Scientists are working on ways to enhance natural carbon storage and develop new technologies to remove CO₂ from the atmosphere.
The carbon cycle will continue long after humans are gone, but the choices we make today will determine what kind of climate future generations inherit. By working with natural processes rather than against them, we can help restore balance to this essential Earth system.