Sitting near the heat of a campfire in the forest, I am holding one end of a stick while a freshly skewered marshmallow begins to brown on the opposite end. I am anticipating a tasty, if a bit gooey, camping treat. As I keep a careful eye on my marshmallow, I bask in the heat from the fire below, as the wood, once part of a living tree, slowly becomes a graying hot ash. This drastic change is also somehow calming. Maybe it is the long-forgotten stirrings of our primitive selves still influencing how we feel security in the fire’s dark-defying glow. In that calm, the puffy marshmallow continues to brown and is starting to look a bit crisp. Another satisfying change.
The chemistry professor in me can’t watch that shift from wood to ash without asking questions. Why is heat leaving the burning wood? Was the heat there all along, just waiting for me to strike a match? The once-growing tree that provided the wood doesn’t know me. It got this heat while patiently growing, absorbing the energy from our sun. That solar energy traveled millions of miles to Earth and a small portion began to power photosynthesis inside this tree’s active cells. How does it stay put until I start my campfire? What causes it to emerge as the wood burns? These questions have answers; they are found in the world of the small, the world that we know, but seldom examine deeply. The world of molecules.
Our universe is made up of small bits of matter we call atoms—an appropriate word to use, as it means “indivisible.” Atoms combine, in myriad specific ways, to produce the molecules we know. As a tree grows it makes new molecules of support (pith, cambium, heartwood), molecules of food (nitrogen, phosphorus, etc.) and molecules that produce color (chlorophyll). The primary source for all this activity is the tree taking low-energy carbon dioxide from air and rearranging it—thanks to that available energy from the sun—into higher-energy molecules. In our not-too-distant past this seemed mystical, unfathomable. Yet this is how plants exist and thrive. That stored-up energy is released when high-energy molecules in wood are provoked to revert back to their original low-energy carbon dioxide—in layperson’s terms, when wood burns. That burning, or molecular reversal, releases the stored energy of the sun. It is that heat from the sun keeping me warm as I hear the crackling and popping of my campfire. It can even sound poetic: “chemical changes are atomic exchanges.”
Looking into the fire and my toasting marshmallow, I see my once-white treat has turned a brownish caramel brown color. These changes happen when amino acids in proteins come near sugar molecules, it only takes a little heat to coax them to combine with each other to create new molecules. This chemistry produces a mixture that is not stable, but changes into other molecules with a brown color, new flavors and aromas. This is the same reaction that causes hamburgers to brown during cooking, roasted green coffee beans to change into the familiar brown we enjoy at the local shop, and a tasty combination of sugars and wheat amino acids to pop out as brown toast to start our mornings.
OK, that is enough cooking. If I leave the brown marshmallow near the fire any longer it will turn into a bitter-tasting black crust as the browned and flavorful molecules break down to the basic black residue of simple carbon atoms.
Did I remember to bring some graham crackers and chocolate to this evening of camping and chemistry? What do you think…? YUM!
Today’s Field Note was written by Bill McLaughlin in the Field Notes Writing Workshop at the Montana Natural History Center. I’m Allison De Jong for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. To find out about upcoming events and programs at the Center, call 327.0405, or visit our website at MontanaNaturalist.org.