Carbon cycle

The carbon cycle is a wonderful process that helps keep our planet healthy. It is part of a bigger group of natural processes called biogeochemical cycles. In the carbon cycle, carbon moves between different places like the living world, soil, rocks, water, and the air around us. Carbon is very important because it is a building block of all living things and is also found in many rocks, such as limestone.

This cycle has two main parts: a fast cycle and a slow cycle. The fast cycle can finish in just a few years, moving carbon between the air, plants, and animals. The slow cycle takes much longer—millions of years—to move carbon through the Earth’s rocks and oceans. Both cycles work together to keep carbon balanced on our planet.

People have changed the carbon cycle for a long time by changing land use and by taking out and burning old carbon stored in coal, petroleum, and gas. Because of this, there is now much more carbon dioxide in the air than before, which helps trap heat and causes global warming. Even though these changes are serious, carbon dioxide is also very important because plants use it to make food through a process called photosynthesis.

Main compartments

The carbon cycle shows how carbon moves through different parts of Earth. Carbon is found in the air, land, water, and inside Earth itself. It moves because of natural processes like plants taking in carbon from the air and oceans absorbing it from the water.

Carbon in the air is mostly found as carbon dioxide and methane. These gases help trap heat and change Earth’s temperature. Carbon dioxide is taken from the air by plants during photosynthesis and can also dissolve in water. Human actions, like burning fossil fuels, have added more carbon to the air over time.

Types of dynamic

There are two types of carbon cycles: a fast one and a slow one. The fast carbon cycle happens in the biosphere. It moves carbon between the air, living things, and the oceans in just a few years. This includes plants taking in carbon from the air and releasing it back when they decompose.

The slow carbon cycle happens in rocks and takes much longer—sometimes millions of years. It moves carbon through the Earth's crust, from oceans to the ocean floor, and deep into the Earth. Over very long periods, carbon can become part of rocks and then return to the surface or the air through natural processes.

Processes within fast carbon cycle

Terrestrial carbon in the water cycle

The movement of carbon on land in the water cycle has several steps. Tiny particles in the air help make clouds. When rain falls, it picks up carbon from the air. Plants take in carbon from the air through a process called photosynthesis and release some of it back. When plants drop leaves or die, their carbon mixes into the soil. Water flowing over plants and soil picks up carbon and carries it away. Rivers and lakes hold and release carbon back into the air. Coastal areas also store and release carbon.

Terrestrial runoff to the ocean

Rivers connect land and ocean, carrying carbon from plants and soil into the water. Some of this carbon returns to the air during the journey, while the rest reaches the ocean. This movement helps balance carbon levels between land and sea.

Biological pump in the ocean

Main article: Biological pump

The ocean helps control carbon levels through a process called the biological pump. Tiny plants in the ocean, called phytoplankton, take in carbon from the water and air. When they die or are eaten, their remains sink deep into the ocean, taking carbon with them. This process moves a lot of carbon from the surface to the deep ocean each year. Some carbon gets buried in ocean sediments and stays there for a very long time.

Viruses as regulators

Viruses help control the carbon cycle by affecting how plants and tiny organisms share food and energy. They are important in freshwater and land environments. Human activities and climate changes have altered how viruses affect the carbon cycle, especially in the last two hundred years.

Processes within slow carbon cycle

Main article: Deep carbon cycle

The slow carbon cycle, also called the deep carbon cycle, is very important. It moves carbon deep inside the Earth. We don't understand it as well as the faster carbon cycle that we see in the air, oceans, and plants. If the deep carbon cycle didn’t exist, carbon would build up in the atmosphere over time. This cycle helps keep Earth’s conditions right for life.

We know there is more carbon deep inside the Earth than on its surface. It is very hard to study because it is far below us. Some experiments and studies using special tools have given us clues about how carbon moves deep inside the Earth. For example, some very special diamonds found in Juina, Brazil show that carbon can travel all the way to the lower part of the Earth. Scientists also use seismology to learn more about carbon deep inside the Earth.

Human influence on fast carbon cycle

Emissions of CO₂ come from many sources and are partly taken up by plants, soil, and oceans. Since the Industrial Revolution and especially after WWII, human actions have changed the carbon cycle by moving carbon from rocks and fuels into the air. We have also changed forests and farmlands and made new chemicals that stay in the environment a long time.

Current changes in climate are making oceans warmer and more acidic, which affects sea life and makes it harder for oceans to take in carbon from the air. The way carbon moves between the air and Earth helps to slow down climate change, but these natural processes might become weaker in the future. Burning fossil fuels is a major cause of adding carbon to the air. Even though some of this carbon is taken up by plants and oceans, a lot stays in the air for many years.

Human changes to land, like cutting down forests for farming, also release carbon into the air. While farming areas store less carbon than forests, planting new forests can help take carbon out of the atmosphere again.