What is the carbon cycle?

We explain what the carbon cycle is and what this biogeochemical circuit consists of. In addition, the importance of this cycle for life.

1. What is the carbon cycle?

A biogeochemical circuit for the exchange of matter (specifically of compounds containing carbon) between the biosphere , pedosphere,  geosphere , hydrosphere and atmosphere of the Earth is known as the carbon cycle . It was discovered by European scientists Joseph Priestley and Antoine Lavoisier , and along with water and nitrogen, is part of the cycles that allow the sustainability of life on our planet.

Since carbon (C) is a key element for life and for most of the known organic compounds, it is involved in numerous substances of organic (and inorganic) origin, in a continuous transmission that allows its reuse and recycling , holding the levels of that element in a global balance.

Carbon in the world exists in different forms and areas : from underground mineral reserves of carbon and inorganic carbon dissolved in seawater, to carbon dioxide in the atmosphere caused by volcanic emissions or the respiration of beings living, as well as the processes of decomposition of organic matter in swamps and other land. For the purposes of the carbon cycle, some of them are considered deposits and other exchange routes.

Broadly speaking, carbon stocks are: atmospheric carbon, the body content of  living things in the biosphere (including marine and aquatic beings), carbon dissolved in seawater and deposited at the bottom of the oceans , and the mineral deposits of the earth’s crust, including deposits of oil and other hydrocarbons.

The exchange routes between these deposits are:

• The fermentation and decomposition processes . The large deposits of organic matter are rich in carbon and in organisms that live from the decomposition and transformation of said matter, obtaining energy in return and releasing gases into the atmosphere such as methane (CH4) or CO2.
• Respiration and photosynthesis . Together with other metabolic biotic processes, these processes respectively release and capture carbon dioxide into the atmosphere, as a byproduct or input of their biochemical pathways. CO2 carbon is fixed in plants and released along with water vapor when animals breathe.
• Oceanic gas exchange . The oceans evaporate by the action of the sun, as established by the water cycle . In this process, the water vapor produced and released into the atmosphere also promotes the exchange of gases between the atmosphere and the ocean, allowing carbon to dissolve in the water, where it is fixed by the photosynthetic plankton.
• The processes of edimentation . Both on land and at sea, the excess carbon in decomposing organic matter, which is not captured and processed by decomposing life forms, will be stacked and sedimented at the bottom of the oceans or in the various layers of the earth’s crust, where it forms fossils, hydrocarbon deposits or reactive sediments.
• The natural combustion or by the hand of humanity . Human industrial processes and spontaneous forest fires should be taken into account in this cycle, since they are responsible for the annual increase in carbon in the atmosphere, in the form of greenhouse gases. This is due to the burning of fossil fuels, the release of organic gases produced by human industry, or the eventual volcanic natural emissions.

All these processes occur at the same time and constitute a delicate balance cycle, which allows carbon to circulate in different environments and as part of substances of very different nature. An interruption of this circuit would mean the impoverishment of numerous vital areas and, possibly, the end of life as we know it.