Introduction to the carbon cycle and biochar with Tom Seiwert

Tom Seiwert is a story-teller, geologist, and cave guide at the Oregon Caves.
Helen and Lori assisted Tom. Kelpie and Daniel documented the class.

By Daniel Dalegowski

Tom presents some background and discusses carbon with the students. Teaching aids include a periodic table, gum-drop molecules, and calcium-based rocks and shells to combine with acid.
What is biochar? One confidant answer was heard: "biochar is disgusting!" That's because the students knew we might be adding urine to charcoal to make biochar! Next: what is carbon; what forms does it take and where is it found? The kids knew a lot already: carbon is sometimes a gas, sometimes solid. Everything alive contains carbon, and if something dead contains carbon, it must have once been alive. For instance, a book. What's it made of? Cardboard, paper, ink: largely tree products; solid carbon in the form of trees.

Gum-drop molecule diagrams from a previous class were used to visualize carbon atoms and their role in common molecules. In addition, a student brought a collection of crystals and other geologic specimens. These were used to demonstrate the relative hardness of rocks: more carbon equals a harder rock, and one can tell which is harder by which one scratches the other. Of course, Tom didn't scratch any of the student's crystals.

A tale of two atoms

Tom's specialty is story-telling. He told the class a story of two carbon atoms. One is on top of a mountain and the other is deep in the ocean. The first carbon atom was breathed out of the lungs of one of the children present. When we inhale we breath mostly nitrogen and oxygen. When we exhale, we breath out nitrogen, oxygen, and also some water vapor and carbon dioxide (CO2). This CO2 that was breathed into the air by a brave volunteer was in turn breathed in by a plant which took the carbon out of the CO2 and, with the energy of the sun, used it to build a small part of a single leaf. Finally, in the Autumn, the leaf fell from the branch of the tree and settled on top of Hope Mountain. Over the winter and following seasons bacteria decomposed the leaf and the carbon atom was deposited in the soil of Hope Mountain.

But what of the other carbon atom; the one deep in the ocean? Many ocean creatures live inside shells. Some find their shells but most create them through chemical reactions inside their bodies. To illustrate, a diagram of a clam was drawn on the board. The clam eats and drinks by taking sea-water into it's body, filtering out the good stuff, and spitting the rest back out. The good stuff is plankton and other tiny sea creatures. Inside the clam's body, calcium, carbon, and oxygen are combined to form calcium carbonate (CaCO3) which the clam makes its shell out of. CaCO3 is also known as calcite and is the chemical that limestone is made of. Limestone is formed over millions of years when shells of sea creatures collect on the sea floor, building and building until they are all smashed together in a sedimentary rock.

The coast-range mountains are made of ancient sea-floor that has been pushed up in the process of subduction below western Oregon. The Oregon Caves were formed when this old sea-floor (lime stone) was exposed to water mixed with CO2. This is carbonic acid, and as it trickles down through the small cracks in the rocks, it dissolves the lime stone, which flows in the water, only to be recondensed in the form of stalactites and stalagmites. Thus, a cave is formed.

The Dome School kids are experts on the Oregon Caves and have favorite parts. Many like Paradise Lost. The Ghost Room, Banana Room, and Popcorn formations are also popular.

Acid demonstration

Carbonic acid is very weak in the scheme of acids. Strong acids can burn a person. Many students had stories to share about friends or family who had, at one point or the other, encountered unfortunate quantities or strengths of acid. Often blisters were the result.

Tom demonstrated the effects of acid when combined with calcium carbonate. He applied a small amount of hydrochloric acid (a very strong acid) to a sea shell. The acid fizzed and some students said they saw vapor coming from the reaction. Tom also applied the acid to a rock he had found just outside the school with similar results. Some rocks, like Serpentine, a local, rare rock, do not react to acids--they do not contain calcium.

The students enjoyed seeing the rocks and shells dissolved. One said it looks like soda fizzing. Baking soda and vinegar were combined, eliciting synchronized "wows!" Various acid and base combinations were discussed. The kids encouraged Tom to put more vinegar and baking soda in, and to try adding some hydrochloric acid, but the combination lost it's drama quickly. Tom explained that this process is the same one that formed the Oregon caves.

It's also the process Tom uses to get pancakes to rise. Tom's pancakes may have been finished in a morning, but the Oregon Caves probably took about one and a half million years to form. Tom explained that if a penny was a year, then the stack of pennies needed to equal one and a half million years would stretch from the classroom to Four Corners (a local intersection a few miles away.)

Lime water activity

The three jars of what will soon be pure lime water
Tom announced that the kids were going to perform an experiment, to which the response was a chorus of "yays!" The experiment will be continued next week. Three mason jars were filled with water. To each of these one teaspoon of calcium hydroxide was added. Calcium hydroxide is similar to calcium carbonate, but the carbonate comes from sea critters, and the hydroxide comes from concrete. One can find stalactites under bridges for this reason.

Three lucky volunteers filled the three bottles. Lots of kids didn't get to fill any bottles, so Tom had them laugh at the bottle-fillers as they returned. None of the bottle-fillers seemed upset by this, and the kids that didn't get to fill a bottle felt privileged that they got to stay. Next, more volunteers got to measure a table spoon of calcium hydroxide into each of the jars. Three more put on the lids, and another three shook the jars.

Tom and Helen explained that the next step will be to decant the liquid in the jars, so that there will be three jars of lime water. To decant is to pour off the liquid while not disturbing the material at the bottom of the jar. The jars of lime water will be kept closed so that no air can mix with the fluid. The lime water that the students started making today will be used in future carbon experiments: for instance, students may blow air into a jar with a straw. The carbon in their breath should give the clear lime water a milky, opaque quality.

At this point the concept of precipitation was visited; we watched as the hydroxide precipitated out the water and collected on the bottom of the jar.

Finally, the kids discussed with Tom and Helen who would label the jars and how they should be labeled. The kids wanted to know what acid was in tomatoes, and also in onions and garlic. No one was sure, but the teachers will come back with an answer next time.

What's charcoal good for?

The background gained in this class is important for understanding the vital link that all forms of carbon play in our environment. Biochar, a sort of fortified charcoal, will be created by the kids over the following weeks. Tom is about to travel to China and he's going to take a small amount of charcoal with him. He asked the students if any of them could figure out why he's taking the charcoal. First answer: "So you get arrested getting on the plane?" No. "To give to other scientists?" No, but that's a good idea. Tom reminded the kids that they will be mixing their pee with charcoal, and this implies that charcoal is good at absorbing liquids and chemicals. Charcoal is like a sponge, and Tom hopes he will not need such a sponge for his stomach, but that is why he's bringing charcoal to China: if he eats something his body cannot handle, he'll get food-poisoning, and one of the best remedies for such an aliment is to consume charcoal. If Tom gets sick the charcoal will absorb the bad bacteria or poison in his stomach. Lots of people take charcoal pills including some of the student's parents.

An interesting comment from a student was that while the chemical reactions we'd seen today involved unstable chemicals combining into more stable forms, some reactions involve the combination of stable chemicals into unstable forms. Often, such reactions are used as weapons. Tom noted that such reactions are used to create electricity as well.

Helen asked "what do we say?" The students gave Tom a synchronized "thank you!" and served themselves lunch.