Carbon Cycle — Definition & Diagrams

What Is the Carbon Cycle?

The carbon cycle is how carbon is circulated around the Earth. If the cycle did not happen, most of the carbon could end up trapped in the atmosphere or deep inside Earth. Different carbon gases are found in the atmosphere. Some examples include carbon dioxide ($CO_{2}$) and methane, which are greenhouse gases. This means that they insulate the Earth and keep heat from radiating out into space.

Carbon in Earth's mantle can be released by geological processes like plate tectonics or volcanic activity. This carbon can remain in the atmosphere or fall to the ground as ash. Ash can then be utilized by plants and also turned into soil.

Carbon gases in the air can also be used by plants during photosynthesis to make sugar and other products. Plants are also able to put carbon back into the atmosphere through a process called cellular respiration.

Carbon stored in sediments like fossil fuels can be released by human activity. These fossil fuels contain carbon from millions of years ago. Burning wood and other organic matter also releases carbon. It can also be passed through food webs by plants and animals when consumers eat producers and release their carbon into the atmosphere as methane.

When rocks on land get weathered by precipitation and erosion, they also release carbon. Runoff from the land transfers to surface water, which cycles carbon into the ocean. The ocean contains a very large amount of carbon in both sediments and living organisms like plankton and fish. Carbon can quickly cycle in and out of the system as plankton or algae photosynthesize and other marine organisms take part in cellular respiration.

The ocean actually contains 50 times more carbon than the atmosphere does. However, as the ocean absorbs carbon dioxide, it becomes more acidic. As the concentration of greenhouse gas entering the atmosphere increases, the pH of the ocean changes. This can greatly harm the organisms living in it.

What Is a Carbon Sink?

A carbon sink, or a carbon reservoir, is able to store large amounts of carbon for a long amount of time. Carbon sinks can remove carbon from the atmosphere through carbon sequestration. Examples of carbon sinks include the ocean, soil, and plants.

How Does Carbon Move Through the Environment?

The carbon cycle is the continuous movement of Earth's carbon. Carbon is found in living things, in the air, in the water, and in many other places. It is necessary for life on Earth.

So, there are two terms that we need to know to discuss this cycle: reservoir and exchange pool.

• A reservoir is a place where a material is stored for a long time, like water in the ocean. Reservoirs are abiotic.
• An exchange pool is where a material is stored for a short amount of time. Think of a small glass of water that evaporates quickly. Exchange pools can be biotic or abiotic.

Carbon moves from reservoirs to exchange pools, then back to reservoirs.

How Does the Cycle Work?

Most of the world's carbon is found in four main reservoirs: the atmosphere, the terrestrial biosphere, the oceans, and sediments. Carbon moves through exchange pools when living things photosynthesize or use cellular respiration. Humans release extreme levels of carbon dioxide into the atmosphere by burning fossil fuels.

Let's begin at the cellular level: cellular respiration releases carbon dioxide. Similarly, decomposing organisms also release carbon into the environment—both the atmosphere and the ground. The carbon in the atmosphere can be absorbed into the oceans if they are cool enough. If the ocean is warm, it actually releases more carbon. Plants also absorb carbon dioxide to use for photosynthesis.

The carbon that is in the soil can be washed into the oceans. The deepest parts of the ocean can store carbon for thousands of years in sediments.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Carbon Cycle}}$ : The movement of carbon between living things and the environment

$\color{#8925AE}{\text{Reservoir}}$ : A place where a material is stored for a long time

$\color{#8925AE}{\text{Exchange Pool}}$ : A place where a material is stored for a short amount of time

(Video) The Global Carbon Cycle

by CrashCourse

Carbon is extremely important in life processes. In this video, Crash Course covers the flow of carbon around the planet.