Carbon is an element. It is the sixth element in the Periodic Table with an atomic number of 6 and an atomic weight of roughly 12. It is also the sixth most abundant element in the Universe.
Carbon is also a term that is used in the medium as a surrogate for a number of other compounds. Before consumption, carbon is meant to imply hydrocarbon fuels or bio-energy sources.
After consumption, carbon is generally used to replace the term carbon dioxide. Hence, we have a "carbon footprint" instead of a "carbon dioxide and other related greenhouse gas footprint."
The term Carbon is used as shorthand.
But carbon is simply an element. It is one of the many found throughout the Universe. Most of the mass of the Universe is made up of hydrogen and helium, with all of the other elements accounting for 0.7 per cent. However, as we are part of that 0.7 per cent we tend to think that the elements around us are pretty important.
On Earth, carbon is the fifteenth most abundant element in the Earth's crust at 0.18% per cent The Earth's crust is dominated by Oxygen, Silicon, Aluminum, Iron, and Calcium with account of 92.5 per cent of that mass with all of the other elements making up the remainder.
However, if you consider that the Earth's crust is estimated at 8.5 x10^20 kilograms, 0.18 per cent is a lot of carbon - 1.5 x10^18 or 1.5 billion billion kilograms.
In one sense, carbon is a minor constituent of the planet. Yes, there is an awful lot of mass tied up in carbon but, in the grand scheme of things, it represents about one tenth of one percent of the planet.
However, when you start to talk about living organisms, carbon is much more abundant and much more important.
Typically, human beings and other animals are about 18 per cent carbon (we are 75 per cent water).
The makes carbon the second most abundant element in the human body (after oxygen) and is why we tend to refer to ourselves as carbon-based life forms. If we were being honest, we are water-based or oxygen-based life forms but that would miss the essential role that carbon plays in living organisms.
It is carbon compounds that make up cell membranes and organelles. It is carbon, nitrogen, oxygen, hydrogen, and phosphorus from which DNA is made. For life, as we know it, carbon is an absolutely essential element.
In the global carbon cycle, the biosphere or living matter is a very small component. The carbon cycle represents the movement of carbon. It is continually recycled and reused throughout the biosphere and lithosphere. Carbon atoms are constantly in a state of flux between the different components of the carbon cycle.
That is not to say that we are making or destroying carbon atoms. There are only so many carbon atoms on Earth.
However, carbon atoms are involved in processes, such as photosynthesis, which creates compounds that move up the energy chain and processes, such as combustion or respiration, which move down the energy chain. Carbon atoms form the backbone of our energy processes.
We don't often think of our life being dependent upon the glucose or sugar molecules that are generated from carbon dioxide and water through the actions of sunlight but that is one way of defining humans. We are heterotrophs, dependent upon the actions of plants for life.
In any case, the carbon atoms involved in both photosynthesis and respiration are the same carbon atoms. There are only so many on the planet and only about 1% are involved in the biosphere.
On the other hand, about 20 per cent of the carbon that is available can be found in fossil form. Fossil carbon is where we find fossil fuel. Again, it is the same carbon atoms but in a slightly different series of compounds.
Fossil carbon generally represents high energy compounds that have been buried away from any source of oxygen. As a consequence, they have not undergone either combustion or respiration. They have not moved along the energy chain.
It is this carbon that we are presently exploiting. We are taking carbon atoms that are found in high energy compounds that were created millions of years ago and converting them to carbon dioxide. The consequence of these actions is that the concentration of the end product, carbon dioxide, is increasing in the atmosphere.
Shifting carbon atoms from one form to another is the basis of much of our energy chain, whether it occurs in living creatures through respiration or by the combustion of petroleum, coal, or natural gas. It is for this reason that we speak of a carbon footprint.
But it is always the same carbon atoms. There are only so many carbon compounds and one day we will run out. Once that happens, we might see our carbon footprint start to decrease.
