Earth's human epoch'

THESE are epoch-making times. Literally. There is now compelling evidence, according to an influential group of geologists, that humans have had such an impact on the planet that we are entering a new phase of geological time: the Anthropocene.

Millions of years from now, they say, alien geologists will be able to make out a human-influenced level in the accumulated layers of rock, in the same way that we can see the imprint of dinosaurs in the Jurassic or the explosion of life that marks the Cambrian.

Now the scientists are pushing for the epoch to be officially recognised. We don't know what is going to happen in the Anthropocene it could be good, even better, said geographer Erle Ellis, a professor at the University of Maryland in the United States. But we need to think differently and globally, to take ownership of the planet.

Anthropocene, a term conceived in 2002 by the Nobel laureate Paul Crutzen, means the age of man, recognising our species' ascent to a geophysical force on a par with earth-shattering asteroids and planet-cloaking volcanoes. Geologists predict that our geological footprint will be visible, for example, in radioactive material from atomic bomb tests, plastic pollution, increased carbon dioxide levels, and human-induced mass extinction.

Geologists and ecologists are already using the term Anthropocene, so it makes sense to have an accepted definition, said Jan Zalasiewicz, a geologist at the University of Leicester, England. But, in this unusual case, formal recognition of the epoch could have wider significance beyond the geology community. By officially accepting that human actions are having an effect on the make-up of the earth, it may have an impact on, say, the law of the sea or on people's behaviour.

In the past, geological changes on a scale big enough to merit a new epoch have been the result of events such as the eruption of a supervolcano or a catastrophic meteor strike things a lawyer might describe as acts of God.

A permanent mark

Now, instead of being just another one of the millions of species on the planet, humans have become the determining factor the guiding, controlling species and many of the changes will leave a permanent mark in the rocks.

The Anthropocene working group of the International Commission on Stratigraphy, the body charged with setting global standards for the fundamental scale to express the history of the earth, met at Burlington House, London, in May to discuss evidence for the planet having crossed into a new geological epoch.

The geological signal will be clear from industrial-scale mining, damming of rivers, deforestation and agriculture, as well as the concentration of carbon in the atmosphere and nitrates in the oceans. Even the presence of the first human-produced chemicals, such as polychlorinated biphenyls (PCBs), radioactive fallout from atomic tests, and the humble plastic bag could be measured millions of years hence. Putting humans at the centre of the planet's activity represents a paradigm shift in the way that geologists usually think of the human species as a mere blip on the long timescale of the earth.

This is not the first time a single species has transformed the planet cyanobacteria did that by oxygenating the earth's atmosphere some two billion years ago but it has taken the self-aware human race to do so knowingly. There have been seven epochs since the dinosaurs died out around 65 million years ago. The last time we passed a geological boundary, entering the Holocene around 12,000 years ago at the end of the last ice age, we were an insignificant species, just one of a couple of hominids struggling to survive in a world where so many of our cousins, such as Homo erectus, had failed to make it.

Now our effect on the climate and our fellow species is having a global impact. The fossil record will reveal a massive loss of plant and animal species, and also the scale of invasive species how we've distributed animals and plants across the globe, Zalasiewicz said. The working group still has some more evidence to gather before it presents its findings to the stratigraphy committee. And then the real battle will commence, Zalasiewicz added. These are slow, nit-picky debates, fraught with acrimony and issues of nationalism. Some members are very cautious, and they think that it's premature to define the Anthropocene because the Holocene has only been around for a short period in geological terms. Other epochs have lasted millions of years.

Others feel the new epoch is upon us and we should come to terms with its implications for the planet. We broke it, we bought it, we own it, Ellis said. Now we've got to take responsibility for it.

Gaia Vince: Guardian News & Media 2011