Discover where carbon is stored on Earth and learn about the major carbon reservoirs in our planet's systems.
Carbon is one of the most important elements on Earth. It is the building block of all living things and plays a crucial role in regulating our planet's climate. But where exactly is all this carbon stored? Scientists identify four major carbon reservoirs — places where carbon is stored for varying periods of time.
The atmosphere contains approximately 850 gigatons of carbon, primarily in the form of carbon dioxide (CO₂) and methane (CH₄). Although this is the smallest of the four main reservoirs, it is incredibly important because atmospheric carbon acts as a "greenhouse gas" that helps regulate Earth's temperature. Before the Industrial Revolution, atmospheric CO₂ levels were about 280 parts per million (ppm). Today, levels have risen to over 420 ppm due to human activities.
The world's oceans contain about 38,000 gigatons of carbon — making the hydrosphere the largest active carbon reservoir. Carbon exists in the ocean as dissolved CO₂, carbonate ions, and bicarbonate ions. Marine organisms like phytoplankton absorb CO₂ through photosynthesis, while shells and coral skeletons store carbon as calcium carbonate. Cold water can hold more dissolved CO₂ than warm water, which is why polar oceans are particularly important carbon sinks. Currently, the oceans absorb about 25% of human-produced CO₂ emissions.
The biosphere includes all living organisms and recently dead organic matter, containing roughly 2,000 gigatons of carbon. Plants are the primary carbon storers in this reservoir — through photosynthesis, they convert atmospheric CO₂ into glucose and other organic compounds. Forests are especially important; the Amazon rainforest alone stores between 150-200 billion tons of carbon. Soil organic matter is also a major component of the biosphere reservoir, containing decomposing plant and animal material that can store carbon for decades to centuries.
The lithosphere (rocks and sediments) is by far the largest carbon reservoir, containing over 100 million gigatons of carbon — that's more than 99% of all carbon on Earth! This carbon is stored in sedimentary rocks like limestone (calcium carbonate), as well as in fossil fuels such as coal, oil, and natural gas. Carbon in the lithosphere is stored for extremely long periods — millions to billions of years. The carbon in fossil fuels came from ancient plants and marine organisms that were buried and compressed over millions of years.
| Reservoir | Carbon Amount | Main Forms |
|---|---|---|
| Atmosphere | ~850 gigatons | CO₂, CH₄ (methane) |
| Hydrosphere | ~38,000 gigatons | Dissolved CO₂, carbonates |
| Biosphere | ~2,000 gigatons | Living organisms, soil organic matter |
| Lithosphere | ~100,000,000 gigatons | Limestone, fossil fuels |
Drag words from the word bank to complete each sentence based on the reading.
Click on each layer of Earth to discover how much carbon is stored there.
Click on any zone above to learn about that carbon reservoir.
Drag each carbon source to its correct reservoir category.
Learn how carbon moves between reservoirs and discover how human activities impact the carbon cycle.
Click each process to learn how it moves carbon and whether it's a source (releases CO₂) or sink (absorbs CO₂).
Click each card to flip it and learn important facts about how human activities affect the carbon cycle. Read carefully — quiz questions come from these facts!
Analyze real climate data and understand how human activities have disrupted the natural carbon cycle.
The graph below shows atmospheric CO₂ measurements (yellow line) and global temperature anomaly (red line) over time. Hover over points to explore the data, then answer the questions.
Match each human activity with its impact on the carbon cycle. Click an activity, then click its matching impact.
Become a carbon atom and journey through Earth's systems! Complete a full cycle to win.
Congratulations on completing the Carbon Cycle Interactive Lab
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