When these systems are damaged or disrupted by human activity, an enormous amount of carbon is emitted back into the atmosphere, contributing to climate change. Carbon is the foundation of all life on Earth, required to form complex molecules like proteins and DNA. This element is also found in our atmosphere in the form of carbon dioxide CO2. The carbon cycle describes the process in which carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere.
Since our planet and its atmosphere form a closed environment, the amount of carbon in this system does not change. Where the carbon is located — in the atmosphere or on Earth — is constantly in flux. On Earth, most carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms.
These are the reservoirs, or sinks, through which carbon cycles. Carbon is released back into the atmosphere when organisms die, volcanoes erupt, fires blaze, fossil fuels are burned, and through a variety of other mechanisms. Humans play a major role in the carbon cycle through activities such as the burning of fossil fuels or land development. Students use labels and arrows to represent processes that move carbon from one reservoir to another.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Photograph by Bruce Dale. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Fossil fuels formed from the remains of ancient plants and animals.
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Educational Resources in Your Inbox Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Soil Respiration: The release of CO2 through respiration is not unique to plants, but is something all organisms do. Because it can take years for a plant to decompose or decades in the case of large trees , carbon is temporarily stored in the organic matter of soil. It may not seem obvious that gasses can be dissolved into, or released from water, but this is what leads to the formation of bubbles that appear in a glass of water left to sit for a long enough period of time.
The air contained in those bubbles includes CO2 and this same process is the first step in the uptake of carbon by oceans. Once in a dissolved form, CO2 goes on to react with water in what are known as the carbonate reactions. The formation of carbonate in seawater allows oceans to take up and store a much larger amount of carbon than would be possible if dissolved CO2 remained in that form.
Carbonate is also important to a vast number of marine organisms that use this mineral form of carbon to build shells. Carbon is also cycled through the ocean by the biological processes of photosynthesis, respiration, and decomposition of aquatic plants.
In contrast with terrestrial vegetation is the speed at which marine organisms decompose. For this reason, very little carbon is stored in the ocean through biological processes. The total amount of carbon uptake 92 Pg C and carbon loss 90 PgC from the ocean is dependent on the balance of organic and inorganic processes. Fossil fuel combustion and land cover change: The carbon fluxes discussed thus far involve natural processes that have helped regulate the carbon cycle and atmospheric CO2 levels for millions of years.
However, the modern-day carbon cycle also includes several important fluxes that stem from human activities. The most important of these is combustion of fossil fuels: coal, oil and natural gas.
These materials contain carbon that was captured by living organisms over periods of millions of years and has been stored in various places within the Earth's crust see accompanying text box.
However, since the onset of the industrial revolution, these fuels have been mined and combusted at increasing rates and have served as a primary source of the energy that drives modern industrial human civilization. Because the main byproduct of fossil fuel combustion is CO2, these activities can be viewed in geological terms as a new and relatively rapid flux to the atmosphere of large amounts of carbon. Another human activity that has caused a flux of carbon to the atmosphere is land cover change, largely in the form of deforestation.
With the expansion of the human population and growth of human settlements, a considerable amount of the Earth's land surface has been converted from native ecosystems to farms and urban areas. Native forests in many areas have been cleared for timber or burned for conversion to farms and grasslands.
Because forests and other native ecosystems generally contain more carbon in both plant tissues and soils than the cover types they have been replaced with, these changes have resulted in a net flux to the atmosphere of about 1. In some areas, regrowth of forests from past land clearing activities can represent a sink of carbon as in the case of forest growth following farm abandonment in eastern North America , but the net effect of all human-induced land cover conversions globally represents a source to the atmosphere.
Geological Processes: Geological processes represent an important control on the Earth's carbon cycle over time scales of hundreds of millions of years. A thorough discussion of the geological carbon cycle is beyond the scope of this introduction, but the processes involved include the formation of sedimentary rocks and their recycling via plate tectonics, weathering and volcanic eruptions.
To take a slightly closer look, rocks on land are broken down by the atmosphere, rain, and groundwater into small particles and dissolved materials, a process known as weathering.
These materials are combined with plant and soil particles that result from decomposition and surface erosion and are later carried to the ocean where the larger particles are deposited near shore. Slowly, these sediments accumulate, burying older sediments below.
The layering of sediment causes pressure to build and eventually becomes so great that deeper sediments are turned into rock, such as shale. Within the ocean water itself, dissolved materials mix with seawater and are used by marine life to make calcium carbonate CaCO3 skeletons and shells.
When these organisms die, their skeletons and shells sink to the bottom of the ocean.
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