Global Change – A Long View

We who teach the introductory-level environmental science courses often single out humans, as a species, for changing the global physical and biological environment. The changes are so great, we say, that a group of geoscientists has been pushing to call our current epoch of geologic time the Anthropocene.

Perhaps we give ourselves too much credit: we are not the first or only living things to affect the global environment. Consider the lowly (?) cyanobacteria. About two billion years ago, these photosynthetic organisms became populous enough to change Earth’s oxygen cycle. Around the same time as a population explosion of cyanobacteria (as seen in the fossil record), oxidized iron minerals start to show up in sediments. This probably means that the amount of molecular oxygen (O2) in the atmosphere increased by a factor of 10-100 over previous levels. You could think of this as “pollution” on a massive scale. (Other examples of biologically-driven changes to Earth’s physical and chemical environment exist; non-human living things still exert a large influence on Earth’s environment in ways you may not expect and in places you don’t expect to see it.)

We should be careful when discussing the human impact on the physical environment. Rather than being a means of judging how “good” or “bad” we are to the planet, a footprint analysis can be a way to engage students with broader themes within the sciences.  Maybe, when we discuss the human footprint in our classes, we should qualify our statements: humans have affected Earth’s environmental systems at a scale disproportionate to our biomass. Or maybe we should couch it in terms of Earth’s history (my preference). After all, the other major biologically-driven change to Earth’s physical environemt – the rise of oxygen in the atmosphere – was one of the most significant events in the history of our planet.