The dawning of the age of Anthopocene

This article first appeared in The Listener, issue 3716, 30 July 2011

As a geology student in the late 1980s, I learnt a mnemonic to remember the various geological periods, epochs and ages that make up Earth’s history. It started with Cambridge (for Cambrian) and ended with horses (for Holocene), with some Jolly Catholics (Jurassic, Cretaceous) somewhere in the middle. Now some scientists are suggesting we add a new geological epoch, the Anthropocene, defined by the impact of human beings on the planet.

The idea that the Earth’s rocks were deposited in a sequence of layers, each representing a different time period and containing distinctive fossils, emerged in the late 18th century. The first full geological timescale, published in 1913, is similar to the timescale used today, from the Precambrian rocks that are host to the first primitive life forms, to the Jurassic rocks in which dinosaur fossils are found, and Quaternary rocks, in which we find the fossils of the first humans along with now-extinct large mammals like woolly mammoths and sabre-toothed cats.

So, why do we need an “Anthropocene”? The word was popularised in 2000 by Nobel Prize-winning atmospheric chemist Paul Crutzen, who suggested the entire Holocene, the epoch that started about 12,000 years ago and is marked by a warm interglacial period and the proliferation of new species, be redefined as the Anthropocene. Crutzen is now on a working group that will report to the International Commission on Stratigraphy (ICS) – which determines changes to the geological timescale – arguing for formal adoption of the Anthropocene as a new geological epoch. There is debate over when the Anthropocene should be defined as starting – at the onset of the agricultural revolution or at the onset of the Industrial Revolution – but there is no doubt that human beings have made their mark on the planet, with some of the biggest impacts being in terms of species extinction, changes to the carbon, nitrogen and phosphorus cycles, and the creation of an “urban stratum” of built, mined, drilled and engineered structures.

But what about New Zealand? I asked GNS Science palaeontologist Hamish Campbell, if another civilisation were to come to New Zealand in 10,000 years’ time, what signs of the Anthropocene would they find preserved in our sedimentary rocks?

“The easiest way to recognise the onset of Anthropocene time in New Zealand, as being the first humans arriving here, would be from changes in pollen abundance,” says Campbell. In many parts of New Zealand, pollen grains – which are much more readily preserved than plant matter – would reflect the change from native forests to grasslands. In terms of animal fossils, we’d see a change from New Zealand’s native avifauna to introduced mammals, with “a preponderance of remains of domesticated animals … an awful lot of hens, pigs, cows, and sheep”. And, of course, humans.

Fossils aren’t the only signs of change. “With the Industrial Revolution we get a very clear metal signal,” says Campbell. Roofing materials brought into New Zealand from the mid-19th century – first copper, lead, zinc and iron, and later aluminium – have leached into our waterways, leaving traces in harbour, lake and estuarine sediments.

In terms of the “urban stratum”, what would remain? “Concrete, bricks, asphalt, metal – they are going to survive,” says Campbell. And pipes. With large areas of east Christchurch about to be abandoned, for example, it’s likely the houses will be demolished and removed, but not the pipes underneath. “The hallmarks of human occupation will be the sewer pipes, water mains and gas pipes,” says Campbell. “They’ve been excavating sewers associated with Pompeii and are finding all the trappings of life at the time, in the form of jewellery and oil lamps that people dropped down the loo at night … nowadays the most common item found in the sewer is the cellphone.” An urban stratum of sewers and cellphones? Let’s hope that a few time capsules are preserved to present a less prosaic remnant of our civilisation.

Fossils are, however, notoriously difficult to make. The natural forces of decay – oxidation, bacterial action and UV radiation – work against the preservation of plant and animal fossils and human artefacts. The best way to preserve something is in a cold, dark, still, muddy environment or beneath deposits from a catastrophic event like a major flood, a mudslide or a volcanic eruption. “Supervolcanoes in the central North Island have the propensity to generate superheated sheets of pyroclastic debris. With the collapse of the eruption column, they just race out across the landscape at up to 800km an hour, almost frictionless. They would just bury everything; you would get instantaneous preservation of cities and towns underneath all this ignimbrite.”

Which is a reminder that no matter how much of an impact we’re having on the natural environment, we’re still at the mercy of physical processes. “We’re powerless when it comes to fighting seismicity and mountain building and volcanism.

Our biggest impact is not so much in physically rearranging the landscape, putting roads and things in; our biggest impact is biological.”

So, does Campbell think the ICS will accept the proposal to declare our current epoch the Anthropocene? “Absolutely. And philosophically, I think it’s quite important. There’s no escaping the fact that we’ve having a massive impact on the planet, and we’re all in this together. The way forward is for societies to plan for, to mitigate against, possible changes. Will recognition of something called the Anthropocene help? I think it might.”

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About Rebecca Priestley

I have a PhD in the history & philosophy of science and I write about science and science history. I live in New Zealand.
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