26 | NewScientist | 8 November 2014

OPINION

Our brave new world Is this the moment to declare that we have entered a new geological epoch created by humans, wonders Jan Zalasiewicz

WHAT is the legacy that short-lived humanity will leave to an almost eternal Earth? The casual observer might point to tourist sights such as the once mighty city of Angkor, now lying ruined amid the Cambodian jungle, or what survives of the great monuments of ancient Egypt.

They are wonderful, of course, but there is another way to address that question. A little-known working group, part of the International Commission on Stratigraphy, recently met to consider if the human imprint on Earth is now so great, and likely to be detectable for so long, that it deserves to be regarded as a geological epoch in its own right. That would be our real legacy.

Such discussion is not new. George Perkins Marsh, North America’s first conservationist, wrote of humans changing the face of the Earth. In 1873 the Italian geologist Antonio Stoppani coined the term Anthropozoic –the era in which humans change the course of geological history. Most geologists declared the idea nonsense. The constructions of civilisation may look impressive, they said, but must surely be trivial when set against the collisions of continents and the growth and disappearance of the oceans. When humans disappear, the world will resume its course, and few of our monuments will be left.

But over the past few decades it has become clear that human activities can have geologically far-reaching effects. Science writer Andrew Revkin suggested we were living in what he called the Anthrocene; John Curnutt of

the US Geological Survey, awed at the transplanting of species across the globe, proposed the Homogenocene; marine biologist Daniel Pauly saw the oceans’ future as one of slime and jellyfish as a result of overfishing and pollution, and invented the Myxocene.

But it was one of the world’s most respected scientists, the Nobel-prizewinning atmospheric chemist Paul Crutzen, who proved most influential. He argued that the Holocene, the geological epoch of post-glacial stability in which civilisation arose, had ended and been replaced by the Anthropocene, an epoch shaped by humans.

The idea took off. The term was used as if it were a formal epoch. It isn’t – but could it become so? A commission of the Geological Society of London signalled the potential in 2008, and now the Anthropocene Working Group, which I am a member of, has been analysing the case. Formalising the Anthropocene would be a big step: the Geologic Time Scale, the backbone of Earth science, is jealously guarded.

Does the evidence stack up? With minerals, there has been

something of a revolution, perhaps the greatest since 2.5 billion years ago, when the rise of free oxygen created a swathe of oxides and hydroxides. Humans have separated out pure metals (a rarity in nature) in million-tonne amounts. Materials scientists have conjured up new minerals: tungsten carbide for ballpoint pens, new garnets for lasers, boron nitride as an abrasive harder than diamond. There are “mineraloids” too, such as glass and plastics.

How many artificial minerals are there? Probably many thousands. By contrast, there are fewer than 5000 recognised natural minerals, most vanishingly rare. We now have vast amounts of these new minerals: around half a trillion tonnes of concrete has been made to date, for example, and over a trillion bricks every year.

With our artificial “rocks” we make the complex urban strata that intermesh with ploughed landscapes on land and the scraped, trawled seafloors of the continental shelves. This human layer penetrates deeply, too, via boreholes and mineshafts so far below the surface they are effectively permanent.

Permeating the forming strata are novel chemical signals. These range from heavy metals to persistent organic pollutants to changed patterns of isotopes resulting from our perturbing of the carbon and nitrogen cycles, to the artificial radionuclides of the nuclear age. The biosphere – which will become the fossil record of the future – has been reshaped by species invasions and

“ The Anthropocene is emerging as a geologically instantaneous planetary reshaping”

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One minute interview

For more opinion articles, visit newscientist.com/opinion

Solar’s foldable futureOlga Malinkiewicz says a change of material could shake up the way we build and use solar cells – by making them bendy

PrOfileOlga Malinkiewicz is co-founder of Saule technologies, a solar-cell start-up in warsaw, Poland. She invented a way to create the cells on ultra-thin foils using novel materials, an approach her company is now trying to commercialise

What’s the special ingredient in the solar cells you’re designing?Perovskites are a large family of materials with a common crystalline structure, and include natural minerals or films synthesised in the lab. today most solar cells are made of silicon, which has to be at least 80 micrometres thick – about the width of a human hair – to convert as much light energy as possible into electricity. Perovskite cells can be just tenths of a micrometre thick, making them ultra-lightweight and very cheap, while still keeping the efficiency of bulkier silicon cells.

What can they do that silicon cells can’t?Our vision for them hinges on the fact that they can be flexible because they’re so thin. they can be printed or sprayed on foils, and because the cells are only 0.2 micrometres thick, they’d be light as air. And they can be semi-transparent or coloured, so you could put them in windows, or have a building that from a distance you don’t see is covered with solar cells but that could produce enough electricity to power itself.

The best silicon cells convert about a quarter of the solar energy falling on them into electricity. Are perovskite cells as good?the theoretical limit for perovskite cells is about 30 per cent, so at least 28 per cent should be possible. they are already at 18.4 per cent. You don’t need complicated equipment to produce these and the materials aren’t expensive. So now, everybody’s started to work on perovskites and progress is much faster.

So could perovskite replace silicon?Silicon lasts 25 or 30 years; so far perovskites have only reached 1000 hours. Fighting silicon would be suicide, and you’d lose before you even start because of the lifetime.

trees get energy from leaves with only about 3 per cent efficiency, but they have a lot of leaves and they are very “cheap” to produce. every year they are exchanged for new ones. my dream is to have solar cells that after some time will degrade like leaves on a tree. Perovskites are partially organic, so it should be possible. if we can get rid of the small amount of lead they contain, it would be easier to make them safely disposable. then you could use the cell for power when you’re camping, for instance, and throw it away after.

Are you at all worried that the potential of perovskites might be overhyped?Perovskites have already proved that they work, so i don’t think this will implode. i really think we can improve them, and even if we can’t they are already good enough to use where you can’t use silicon. when i look around, i imagine covering everything with perovskites.

Could your work help unearth other promising materials?the particular perovskite we’re using now is one iBm was testing for transistors and other applications 20 years ago. the only thing they didn’t try was solar cells. if they had, we might be living in a completely different world. i think there might be a lot more materials like that out there.Interview by Andy Extance

extinctions. The Anthropocene is emerging as a real phenomenon, a geologically instantaneous planetary reshaping to rank with some of the great perturbations of the deep past.

But should it be formalised? This is a harder question. While detectable human impacts extend back thousands of years, the step change to the Earth system really began with the industrial revolution, and accelerated in the mid-20th century. Most epochs are measured in millions of years. To have one measured in decades is without precedent in geology. We are seeing it, too, as it evolves, our observational data complementing the geological clues being preserved in strata now forming.

But, grafted on to a similarly complex archaeological record, it can make the choosing of a single Holocene/Anthropocene boundary seem crude, akin to the ruler-straight borders beloved of colonial governors. Some key drivers of the Earth system, too, have only just begun to alter. Carbon dioxide levels may have shot up by a third, probably faster than at any time in the past. But the oceans and rocks are soaking up much of the extra heat, so we are still enjoying a more or less typical interglacial climate. When warming does kick in seriously over coming centuries, Anthropocene change will ratchet up profoundly. Wait for this, some say, before formalising the term.

The Anthropocene, formal or informal, seems here to stay. Its impact is substantial, reframing the debate over how humans and nature are related. In providing the biggest backdrop for global change, too, it could help us manage that change. In the end, though, names should reflect perceived scientific reality. If the world’s geology has truly changed, then the nomenclature should follow suit. n

Jan Zalasiewicz is a geologist at the university of Leicester, uK

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