We owe the existence of biochar to the incredible chemical process called pyrolysis. Under pyrolysis, organic matter is heated with little or no oxygen so that the carbon within the matter is left almost untouched. A “skeleton” of the plant material is left in what used to be its cell walls, making for a myriad of microscopic carbon catacombs.
The word pyrolysis comes from the Greek terms “pyro” meaning “fire,” and “lysis” meaning “separation.” For our purposes of making biochar, heat causes a reaction in organic plant matter that separates carbon from tars, hydrogen and methane. The Hydrogen and methane are forced out as what we call “syngas” or off-gasses, and burned as fuel creating more heat. When the reaction is complete the biomass has been transformed into biochar with all its wonderful properties, almost like a caterpillar morphing into a butterfly.
When biomass is heated it goes through a couple stages before turning into char:
Pyrolysis naturally occurs in our environment and is partially responsible for the landscapes we are familiar with today. Lightning has started fires on our planet for millions of years. Those fires have indirectly distributed biochar into the soil over the years. Anytime there is a forest or brush fire there is a small percentage of the combustible matter that burns incompletely without oxygen leaving char instead of ashes. Parts of plant root structures can burn underground where voids of oxygen exist. Or, burning matter can become buried by ash and other falling debris shutting off its access to oxygen. Another example of this is when lava flows encrypt parts of trees and plants to burn without an oxygen supply. In yet another scenario, rain could quench a forest fire, inhibiting the matter from transitioning from char to ash. In all of these cases, pyrolysis occurs naturally when organic plant matter burns incompletely, creating biochar and enriching the soil. Although forest fires are commonly known for death and destruction, they have indirectly played a large role in increasing the richness of our soils.
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Gore's book Our Choice pointed out some ways in which the climate change problem might be solved, with biochar being one piece of the puzzle.