An investigator set up a laboratory experiment to monitor gaseous exchange in a sealed terrestrial microcosm. A sealed glass jar containing soil, a small green plant (Coleus), and an earthworm was equipped with a sensitive carbon dioxide ($C{O}_2$) sensor connected to a continuous data logger.

For the first 5 days, the jar was kept in a climate-controlled incubator under constant, bright artificial light. At the end of Day 5, the light source was switched off completely, leaving the jar in total darkness. On Day 8, the earthworm died.