I wrote yesterday about the North American cod stocks that have practically disappeared during the last century as a result of overfishing. Needless to say, this is just one of many species that humans have had a seriously detrimental effect upon in their shaping of the Earth. An article from The Economist this May discusses the geological forces that humans have had on the Earth, focusing on topics like the carbon cycle or nitrogen fixation rather than species extinction.

Paul Crutzen and Eugene Stoermer coined the term “Anthropocene” in 2000 to classify what they see as a new age on the geological time scale, and the fairly abrupt and sharp decline of cod may be one of the many changes visible in the fossil record thousands or millions of years from now. As you can see in the image below, we are currently in the Holocene, but Crutzen and Stoermer, along with many other scientists, including several of those in the International Commission on Stratigraphy (which arbitrates the geological time scale), believe that we have entered an age primarily shaped by Homo sapiens.

Image from The Economist

The clearest evidence for the system working differently in the Anthropocene comes from the recycling systems on which life depends for various crucial elements. In the past couple of centuries people have released quantities of fossil carbon that the planet took hundreds of millions of years to store away. This has given them a commanding role in the planet’s carbon cycle.

I’m sure most of you have heard about the carbon dioxide evidence more than enough times, so I’ll go straight to the information that surprised me most:

By adding industrial clout to the efforts of the microbes that used to do the job singlehanded, humans have increased the annual amount of nitrogen fixed on land by more than 150%. Some of this is accidental. Burning fossil fuels tends to oxidise nitrogen at the same time. The majority is done on purpose, mostly to make fertilisers … About 40% of the nitrogen in the protein that humans eat today got into that food by way of artificial fertiliser. There would be nowhere near as many people doing all sorts of other things to the planet if humans had not sped the nitrogen cycle up … It is also worth noting that unlike many of humanity’s other effects on the planet, the remaking of the nitrogen cycle was deliberate.

Add to these chemical changes the countless species lost, domesticated, and allowed to become invasive; the millions of miles of concrete and metal that will become part of the geological record; the alterations in climate; and several other effects that we’ve had on our planet, and the classification of our age as the “Anthropocene” doesn’t necessarily need to remind us of geocentrism. At least in this case we have accurate evidence to back the theory up.