Some scientists are trying to name our current geologic epoch after us — calling it the Anthropocene. That's no brag, because most of the changes we're making to our planet are embarrassing.
We've caused huge shifts in the plants and animals sharing the planet with us, driven many species to extinction, left a layer of radioactive fallout from exploding nuclear bombs, accidentally changed the composition of our atmosphere, and left a layer of plastic that will in all likelihood still be around in a million years.
Long after time and erosion have turned all our feats of art and engineering to dust, our mess will remain. Naming this era after ourselves is more of a confession. That acknowledgement is a first step toward strategies for minimizing our damaging influence.
A fascinating feature in Nature this month describes the search for what scientists call a golden spike - a marker somewhere on the planet displaying a clear, sharp signature of significant change that would mark the dawn of the Anthropocene. What makes the process interesting isn't what they settle on as a starting point, but what it's revealing about the way humans have become an earth-changing force, and how long human-wrought changes will persist. With that understanding could come strategies for minimizing our damaging influence.
These scientists are coming to favour atomic bomb blasts of the 1950s, which are leaving a long-lasting layer of isotopes in lake beds and deposits of ice. People have also considered the advent of widespread chicken farming, which leaves behind the bones of almost 60 billion birds each year.
There is a subjectivity to this process, said Planetary Scientist David Grinspoon, whose book Earth in Human Hands makes a case for the Anthropocene. A person exploring Earth 50 million years from now may not find any obvious signs that we were here, he said, but if they were trained archaeologists and did some digging, they would see that something extraordinary happened.
Naysayers argue that we don't warrant our own geologic era because we are too short-lived a species. We've only been around 2,00,000 years, and for most of this time we did nothing to cause lasting change. It wasn't until 50,000 years ago that people started to spread around the globe, leaving in our wake a wave of extinctions of the animals we liked to eat. And it was only in the last century - insignificant in geologic time - that we've really started adding new materials, such as plastics, to the geologic strata. Geologic time is long, and our existence short, at least so far.
But we can already know that our influence on the planet will last into geologic time. The nuclear remnants of our bomb blasts will last for hundreds of thousands of years, and so will traces of those mountains of plastic we've been throwing away, some of which is already forming a new kind of stone, dubbed plastiglomerate. Scientists estimate that human-generated changes in the chemistry and temperature of our oceans will persist for thousands of years after we learn how to stop burning fossil fuel.
In Greenland's ice cap, layers dating back to the Roman era show contamination with industrial lead. Leaded gasoline from the 20th century will leave an even bigger layer that also includes cadmium, arsenic and chemical changes that took place when the ozone layer sprung a hole. (While the edges of the ice are melting fast, the cap itself, and buried traces of our pollution, could last another million years.)
Even more profound will be the change in the fossil record of life. The United Nations recently estimated that, globally, human activity is likely to cause a million species to go extinct. We don't really know how many species exist now; biologists have cataloged about two million but estimate a total of around 10 million.
Another recent study showed that we've already radically changed the populations of living things — destroying 83 per cent of all wild animals and half of wild plants. Currently, researchers estimate, 96 per cent of mammals today are humans or livestock, and only 4 per cent are wild animals.
To make the Anthropocene official, a committee called the Anthropocene Working Group will need to agree on a golden spike and create a proposal, which would eventually come up for approval from the International Union of Geological Sciences. But even without official sanction, the idea is catching on in the popular imagination.
Back in the 20th century, when I wrote about the predictions that greenhouse gases were warming the globe, people accused me of being arrogant for even thinking human beings could affect this vast planet. But the earth is not, as long believed, too vast to be changed by humans, and with a population of 7 billion and climbing, we are not too small to leave an indelible mark.
