We all know about Earth’s water cycle. We are taught the water cycle in elementary school, but did you ever learn about Earth’s fascinating carbon cycle? Earth’s carbon cycle describes the way the element carbon moves between the Earth’s biosphere, hydrosphere, atmosphere, and geosphere. There is both a fast and slow carbon cycle in play. The fast carbon cycle is when plants and phytoplankton (microscopic organisms in the oceans) take in carbon dioxide (CO₂) from the atmosphere and combine CO₂ and water to form sugar (CH₂O) and oxygen. Animals then use that oxygen through respiration and release carbon dioxide back into the atmosphere. The fast carbon cycle also explains the changes in the seasons in the Northern hemisphere, where most land is located. These regions have higher and lower CO₂ levels across the seasons, with higher CO₂ levels in winter and lower CO₂ levels beginning in the spring as plants begin to grow. These rises and falls are like Earth’s inhale and exhale.
In contrast, the slow carbon cycle has a vastly different timescale and is an interplay between Earth’s geologic processes and land erosion. Let’s go back in time to the Permian-Triassic boundary (or P-T boundary), which occurred 252 million years ago. The Siberian Traps are believed to be the primary cause of the Permian – Triassic extinction event. This period was nicknamed the Great Dying because it caused the extinction of over 90% of marine species and 70% of land species. The likely cause of the extinction was elevated temperatures in the marine realm that created widespread oceanic anoxia (low oxygen levels) and ocean acidification due to the extensive amount of carbon dioxide emitted by the eruption of the Siberian Traps. The extremely active volcanism during that time created the Siberian land mass, covering about five million square kilometres. It was not a good time for life on the planet, but for every action, there is a reaction, and increased volatility in the climate created more precipitation. Rain with a high amount of CO₂ forms carbonic acid, which increases rock erosion on land. The rock erosion releases calcium, magnesium, potassium, or sodium ions which reach the ocean through rivers. Here, marine organisms, such as coral, use them to build their shells (calcification). When these marine organisms die and are buried without decomposition, that carbon is removed from the carbon cycle. Until, of course, humans dig it up as fossil fuel, burn it and add that stored carbon back into the atmosphere.
It is heartening to learn that Earth can bring the carbon cycle back into equilibrium over time, but that is a geologic time frame, not a human timescale. Thus, this long carbon cycle will not help us reduce carbon emissions resulting from burning fossil fuels. This means it is up to humans to make the transition to a non-fossil fuel energy system in a very short period to avoid triggering feedback loops that could very well cause the sixth great extinction that life on Earth has had to contend with.
By Gaby Kalapos, Executive Director