Science and You
Todd Whitcombe
Dear Reader:
Please note that this column ends in an "arrow" pointing to the carbon atom that is the central feature of the column.
Cheers, Todd
Billions of years ago - no one knows how many - eight? 10? - three helium nuclei came together in the core of a star and formed the nucleus of a carbon atom.
It wasn't an atom at this point because in the maelstrom that is the core of a star, nuclei can not hold onto their electrons. There is just a sea of electrons supporting a floating mass of nuclei, all waiting to be born as atoms.
Some billions of years later - no one knows how many - its birth place, that unknown star, exploded and all of the material inside was ejected across space forming a nebula of atoms from which the next generation of stars would emerge.
In this nebula, our little carbon atom was attracted to a particular gravity well. It was drawn into a planetesimal that collected with other planetesimals to eventually form the planet Earth. As the nascent Earth cooled, our carbon atom was ejected from the surface and formed part of the original atmosphere where it combined with two oxygen atoms to give carbon dioxide.
That molecule of carbon dioxide floated free in the atmosphere for a long time but was eventually trapped in the oceans where it combined with calcium to form the limestone - calcium carbonate - underlying much of British Columbia. Our little carbon atom had finally found a home as rock and there it stayed for a billion years.
About 40 years ago, though, the limestone was mined and used in a lime kiln, such as those found at our local pulp mills. A lime kiln takes crushed limestone rock and heats it to about 1,100C.
At this temperature, the calcium carbonate breaks down to carbon dioxide and calcium oxide. As a result, our little carbon atom was once again free to roam as a gas molecule. It wandered through the kiln to the stack and out into the air. The winds of the day carried our atom into the downtown region where it was inadvertently sucked in and out of the lungs of several people in quick succession. In fact, 0.038 per cent of the air that we breathe daily is carbon dioxide - although that number was only 0.028 per cent 40 years ago.
Still, carbon dioxide is the end product of metabolism and not useable by the body.
So, despite being absorbed by the blood in some people's lungs, it was for only a moment - a quick trip around the body as a buffer - before our carbon atom was on its way again. Our carbon was destined for other, more lofty goals.
It had many miles to go before it was going to settle down again. In fact, it wandered further south where it came across a stand of trees.
This is where our carbon atom participated in another chemical transformation. It got caught in the needle of one of the trees, and since trees use carbon dioxide as a starting point for making sugar, that was to be its fate. Our carbon atom suddenly found itself whisked away to be used in a biochemical reaction. The oxygen atoms fell away and the carbon found a new home, through photosynthesis, in a small ring with five other carbon atoms. It was now part of a sugar.
In particular, glucose, which is one of the most important of all sugars, as it is nature's way of storing energy for future use. It is also a key component in the construction of cellulose, the building material from which trees and plants are made. This particular ring of carbon atoms was destined to become part of the structural backbone of the tree, holding the tree rigid and strong throughout the years. There it sat, doing its part.
Last year, the tree was harvested and our carbon atom was once more on the move. Travelling by truck to the chipping plant, part of the tree was converted to chips, destined for one of the pulp mills. Being part of the cellulose, our carbon atom and its ring-mates were freed from their lignin cage to become pulp. Not all of the carbon in a tree gets converted to pulp, as some of it gets chewed up and results in the feed stock for various furnaces and such. But our little carbon found its way out the door.
Ground up and spit out, our carbon became part of a roll of newsprint, used to print newspapers such as this one. In fact, that carbon atom that started off billions of years ago with the fusion of helium nuclei in a distant star and found its way through the void of outer space to the carbonate rock of the Earth, and eventually into the living organisms of our biosphere, has finally settled down again as part of this very newspaper - and is right here ->
