The Carbon Cycle
Scientists consider 99.9% of all organisms on the planet to be carbon-based life. Those organisms need carbon to survive. Whether the carbon is in the form of a sugar or carbon dioxide gas, we all need it.
Unlike energy, which is supplied by the sun and is lost to the atmosphere as heat, carbon is continuously cycled and reused. The Earth only has a fixed amount of carbon. The carbon cycle is a form of recycling. The carbon cycle is when carbon cycles through the atmosphere, bodies of water, soil, plants, and animals.
Unlike energy, which is supplied by the sun and is lost to the atmosphere as heat, carbon is continuously cycled and reused. The Earth only has a fixed amount of carbon. The carbon cycle is a form of recycling. The carbon cycle is when carbon cycles through the atmosphere, bodies of water, soil, plants, and animals.
Let's start with plants...Plants are a good starting point when looking at the carbon cycle on Earth. Plants have a process called photosynthesis that enables them to take carbon dioxide out of the atmosphere and combine it with water. Using the energy of the Sun, plants make sugars and oxygen molecules.
All of the non-photosynthetic creatures on the planet (like animals and bacteria) use the oxygen. Every creature on the planet uses the sugars and starches created by plants. |
Satellites & photosynthesis |
Animals eat the plants...
Animals are non-photosynthetic creatures. They are not able to create their own food. Instead, they eat plants or other animals.
The sugars and starches they eat are broken down by a process called metabolism. When you break the sugars down, you get energy, water, and carbon dioxide molecules. The carbon dioxide then returns to the atmosphere when animals breathe. Plants can then use it again. There are also decomposers involved in the carbon cycle. They break down organic material such as dead animals, poop, or leaves.
Decomposers are able to break down the chemical compounds inside the body. They release carbon dioxide, which then becomes available for plants once again. |
Remember decomposers? |
Time lapse of mushrooms |
|
|
Fossil Fuels
Sometimes the decomposers don't break down organic material. There are great oil fields under the surface that are made of plants and animals that did not decompose millions of years ago. This is what you know today as "fossil fuels."
|
Burning these fossil fuels over the last few hundred years -and especially in the last 100 years- has increased the amount of carbon dioxide in the atmosphere. It has increased a lot faster than the ocean or plants can absorb it.
This is causing the average temperature around the globe to increase a little bit, which causes some severe weather patterns. You learned about this 'greenhouse effect' last year. This carbon may eventually return to the carbon cycle, but geological (Earth) processes are very very slow. |
Carbon Dioxide levels in the atmosphere over 1 year |
Global Temperatures 1880-2011 |
|
|
The Ocean as a Carbon Sink
Oceans can absorb a lot of carbon dioxide. Oceans reduce the amount of carbon dioxide in the atmosphere and bring carbon atoms into the ocean system. Many CO2 molecules that "diffuse" into ocean sea surface diffuse back to the atmosphere in very short time scales.
However, carbon atoms can be pulled down through ocean currents. They can stay in the ocean for time scales of hundreds to thousands of years if they fall deep enough. If some carbon atoms eventually make it to the bottom of the ocean sediment, they can be stored for time scales of millions of years.
Organisms in the ocean use the carbon dioxide. Phytoplankton use the carbon dioxide in photosynthesis. In addition, when the carbon dioxide mixes with water, it can change. The carbon becomes available to make another substance called calcium carbonate. This is the stuff shells are made of. So many ocean animals rely on carbon for their protection.
We say that the ocean is a "carbon sink" because it collects a lot of carbon, and sometimes the ocean keeps it down there. So, the carbon sinks.
However, carbon atoms can be pulled down through ocean currents. They can stay in the ocean for time scales of hundreds to thousands of years if they fall deep enough. If some carbon atoms eventually make it to the bottom of the ocean sediment, they can be stored for time scales of millions of years.
Organisms in the ocean use the carbon dioxide. Phytoplankton use the carbon dioxide in photosynthesis. In addition, when the carbon dioxide mixes with water, it can change. The carbon becomes available to make another substance called calcium carbonate. This is the stuff shells are made of. So many ocean animals rely on carbon for their protection.
We say that the ocean is a "carbon sink" because it collects a lot of carbon, and sometimes the ocean keeps it down there. So, the carbon sinks.