Human impact on the Earth is now so profound that a new geological epoch – the Anthropocene – needs to be declared, according to an official group of experts.
They presented the recommendation to the International Geological Congress in Cape Town yesterday.
The new epoch should begin about 1950, they say, and is likely to be defined by radioactive elements dispersed by nuclear bomb tests.
Other signals, including plastic pollution, soot from power stations, concrete and even bones left by the worldwide spread of the domestic chicken are also under consideration.
The current Holocene epoch is the 12,000 years of stable climate since the last ice age during which all human civilisation developed.
The acceleration of carbon dioxide emissions and sea-level rise, mass extinctions and the transformation of land by deforestation and development since the mid-20th century mark the end of that slice of geological time, the experts argue.
“The significance of the Anthropocene is that it sets a different trajectory for the Earth system, of which we of course are part,” says Professor Jan Zalasiewicz, a geologist at the University of Leicester and chair of the Working Group on the Anthropocene, which started work in 2009.
Professor Chris Rapley, a climate scientist at University College London and former director of the Science Museum in London says: “The Anthropocene marks a new period in which our collective activities dominate the planetary machinery.
“Since the planet is our life support system – we are essentially the crew of a largish spaceship – interference with its functioning at this level and on this scale is highly significant.
“If you or I were crew on a smaller spacecraft, it would be unthinkable to interfere with the systems that provide us with air, water, fodder and climate control. But the shift into the Anthropocene tells us that we are playing with fire, a potentially reckless mode of behaviour which we are likely to come to regret unless we get a grip on the situation.” Rapley is not part of the WGA.
To define a new geological epoch, a signal must be found that occurs globally and will be incorporated into deposits in the future geological record.
For the Anthropocene, the best candidate for such a “golden spike” is radioactive elements from nuclear bomb tests, blown into the stratosphere before settling down to Earth.
Other spikes being considered as evidence of the onset of the Anthropocene include tough, unburned carbon spheres emitted by power stations. “The Earth has been smoked, with signals very clearly around the world in the mid-20th century,” says Zalasiewicz.
Other candidates include plastic pollution, aluminium and concrete particles, and high levels of nitrogen and phosphate in soils from artificial fertilisers.
The domestic chicken is a serious contender to be a fossil that defines the Anthropocene for future geologists.
“Since the mid-20th century, it has become the world’s most common bird. It has been fossilised in thousands of landfill sites and on street corners around the world,” Zalasiewicz says. “It is is also a much bigger bird with a different skeleton than its pre-war ancestor.”
The 35 scientists on the WGA – who voted 30 to three in favour of formally designating the Anthropocene, with two abstentions – will spend the next two to three years determining which signals are the strongest and sharpest. They must also decide a place which will define the start of the epoch.