The carbon cycle
The carbon cycle
The element carbon is found all over the Earth; In all that lives... Out in the ocean... Down in the ground... ... and a little bit in the atmosphere. In the atmosphere carbon is bound to oxygen, in the form of carbon-dioxide: C-O-two.
When carbon is part of something living, it can take many forms; a DNA molecule, protein, fat... or a carbohydrate. More than half of the weight of plants is carbon. Carbon in nature is constantly moving: between atmosphere, plants, animals, ocean, and ground... ... round and around, in a cycle.
A cycle that all life on earth is dependent upon. From the atmosphere, plants take up carbon-dioxide, through photosynthesis, and produce carbohydrates. When a plant dies, it decomposes; and most of the carbon again forms carbon-dioxide that enters the atmosphere. Or, an animal comes and eats the plant - to get energy, and to grow. The same carbon atoms that were in the atmosphere are now part of the animal's body!
When the animal breathes, that too is part of the carbon cycle. The exhaled air contains carbon-dioxide, formed when the body metabolizes carbohydrates. Other carbon atoms exit in the animal's droppings. When the animal dies, the same thing happens as with the plant and the droppings: it decomposes. Some of the carbon atoms sink into the ground, where they can stay for quite some time.
But most of the carbon makes it out to the atmosphere, one way or another. The same amount of carbon-dioxide released from all the dead plants is taken up by all the living plants. The same thing happens in the ocean. Seaweed and phyto-plankton absorb carbon-dioxide from water near the surface, using photosynthesis. Carbon is bound in the plants, which are eaten by ocean animals, carrying it along the food chain.
When plants and animals die and sink to the ocean floor, they take the carbon with them. Most of it bubbles up as carbon-dioxide, but some can get trapped under ***, and slowly get pushed further and further down. After millions of years it can be so compressed, that the carbon compounds in the plants and animals turn into oil and gas. A small fraction of the carbon disappears down into the Earth's crust, but most of the carbon atoms form carbon-dioxide. Just as on land, it's the animals' breathing, and the decomposition of living tissue and excrement that form carbon-dioxide.
Carbon-dioxide molecules move between the water and the atmosphere. Normally, about as much carbon-dioxide moves from the air to the water, as the other way around. So, it's all tied together: the air, plants, animals, oceans, and the ground. It's the plants - on land and in water - that absorb the carbon-dioxide. And it's respiration, metabolism, and decomposition, that lets it out again.
Some carbon is in the atmosphere, as carbon dioxide. And some is bound in the Earth's crust. There are more ways that carbon is freed up. Burning something also releases carbon - again as carbon-dioxide. And when people mine oil, coal, and natural gas from the ground, and combust them, large amounts of carbon-dioxide are released.
This distorts the balance in the carbon cycle -- because the plants can't absorb all that extra carbon-dioxide that we release. This increased carbon-dioxide content in the atmosphere is the major reason for the changes in climate we are observing. So, in order to deal with climate change, we must find ways to restore balance in the carbon cycle.