In a rare moment in an early Rover reconnaissance mission to Mars, carbon dioxide (CO2) was released from a soil sample during a scientific test and was thought to indicate the presence of microbes. Excitement quickly faded to puzzlement, then dismay, as it was realized that a glitch in the expensive on-board lab had produced inorganic CO2. Chemicals used for the soil extract triggered release of inorganic CO2, perhaps from the ubiquitous magnesite (MgCO3) found in Martian soil.
On Earth, the release of carbon dioxide from moist soil due to microbial activity is so pervasive that it is difficult not to observe it. We don’t have the problem they do on Mars trying to distinguish biological CO2, in an atmosphere containing 96 percent CO2, from non-living sources. In science we call this dilemma “distinguishing small differences between large numbers.” Here on Earth, CO2 in the atmosphere is only 0.04 percent, and climbing just barely perceptibly, making it relatively easy to distinguish biological CO2. Curiously, almost nobody is doing it.
Borrowing From the Past
I learned about soil CO2 respiration working on a graduate program in Sweden investigating fertilizer and crop effects on soil biology. Agronomists in the 1950s set up farm plots and maintained them for decades, enabling later researchers such as myself to observe the long-term effects of differing soil management.
In the process, I discovered a trove of even earlier Swedish work on soil respiration. Continue Reading →