When Humans Took Over the World

Fifteen years ago, two prominent researchers suggested that the earth has formally entered a phase of human domination.  Unless there's some unforeseen calamity caused by volcanic activity or a meteor, they argued, "mankind will remain a major geological force for many millennia, maybe millions of years, to come."  Nobel prize-winning chemist Paul Crutzen and University of Michigan biologist Eugene Stoermer called this new episode in planetary history the Anthropocene Epoch. The idea has been gaining steam in both the scientific and mainstream press for several years.

Enough scientists have bought into the idea that this week, the journal Nature dedicates more than nine pages to the next logical question:  if we have crossed into the Anthropocene—which "appears reasonable," they write with understatement—when did it begin?

Geologists are quite insistent on physical evidence.  Wherever possible, each of the planet's eons, eras, periods, epochs, and ages are distinguished with a "golden spike," a physical marker somewhere in rock, glacier, or sediment that signals evidence of big changes in the earth's operating system.  It needn't be gold, or even a spike, but without satisfying the International Commission on Stratigraphy's requirements (which includes several additional procedural hurdles), there will be no new epoch.

The Nature article, by Simon Lewis of University College London and Mark Maslin of the University of Leeds, evaluates nine possibilities that others have put forward as the starter's pistol of the Anthropocene Epoch. The episodes reach as far back as tens of thousands of years ago, when people hunted large mammals to extinction. Others are as recent as the post-World War II period, when such "persistent industrial chemicals" as plastics, cement, lead, and other fruits of the laboratory started to find their way into nature.

The authors ultimately dismiss all but two of the examples because the events were too local (rice farming in Asia) and happened over too long a time span (the extinction of large mammals), which are two main obstacles to a golden spike. The two dates that meet their standard are 1610 and 1964.

Read more at When Humans Took Over the World