The New Scientist blissfully imagines a world in which humanity has become extinct.

Humans are undoubtedly the most dominant species the Earth has ever known. In just a few thousand years we have swallowed up more than a third of the planet’s land for our cities, farmland and pastures. By some estimates, we now commandeer 40 per cent of all its productivity. And we’re leaving quite a mess behind: ploughed-up prairies, razed forests, drained aquifers, nuclear waste, chemical pollution, invasive species, mass extinctions and now the looming spectre of climate change. If they could, the other species we share Earth with would surely vote us off the planet.

“Now just suppose they got their wish. Imagine that all the people on Earth – all 6.5 billion of us and counting – could be spirited away tomorrow, transported to a re-education camp in a far-off galaxy. (Let’s not invoke the mother of all plagues to wipe us out, if only to avoid complications from all the corpses). Left once more to its own devices, Nature would begin to reclaim the planet, as fields and pastures reverted to prairies and forest, the air and water cleansed themselves of pollutants, and roads and cities crumbled back to dust.

“The sad truth is, once the humans get out of the picture, the outlook starts to get a lot better,” says John Orrock, a conservation biologist at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California…

Pretty quickly – 24, maybe 48 hours – you’d start to see blackouts because of the lack of fuel added to power stations,” says Gordon Masterton, president of the UK’s Institution of Civil Engineers in London. Renewable sources such as wind turbines and solar will keep a few automatic lights burning, but lack of maintenance of the distribution grid will scuttle these in weeks or months. The loss of electricity will also quickly silence water pumps, sewage treatment plants and all the other machinery of modern society.

The same lack of maintenance will spell an early demise for buildings, roads, bridges and other structures. Though modern buildings are typically engineered to last 60 years, bridges 120 years and dams 250, these lifespans assume someone will keep them clean, fix minor leaks and correct problems with foundations. Without people to do these seemingly minor chores, things go downhill quickly…

With no one to make repairs, every storm, flood and frosty night gnaws away at abandoned buildings, and within a few decades roofs will begin to fall in and buildings collapse. This has already begun to happen in Pripyat. Wood-framed houses and other smaller structures, which are built to laxer standards, will be the first to go. Next down may be the glassy, soaring structures that tend to win acclaim these days. “The elegant suspension bridges, the lightweight forms, these are the kinds of structures that would be more vulnerable,” says Masterton. “There’s less reserve of strength built into the design, unlike solid masonry buildings and those using arches and vaults.”

But even though buildings will crumble, their ruins – especially those made of stone or concrete – are likely to last thousands of years. “We still have records of civilisations that are 3000 years old,” notes Masterton. “For many thousands of years there would still be some signs of the civilisations that we created. It’s going to take a long time for a concrete road to disappear. It might be severely crumbling in many places, but it’ll take a long time to become invisible.”..

All things considered, it will only take a few tens of thousands of years at most before almost every trace of our present dominance has vanished completely. Alien visitors coming to Earth 100,000 years hence will find no obvious signs that an advanced civilisation ever lived here.

Yet if the aliens had good enough scientific tools they could still find a few hints of our presence. For a start, the fossil record would show a mass extinction centred on the present day, including the sudden disappearance of large mammals across North America at the end of the last ice age. A little digging might also turn up intriguing signs of a long-lost intelligent civilisation, such as dense concentrations of skeletons of a large bipedal ape, clearly deliberately buried, some with gold teeth or grave goods such as jewellery.

And if the visitors chanced across one of today’s landfills, they might still find fragments of glass and plastic – and maybe even paper – to bear witness to our presence. “I would virtually guarantee that there would be some,” says William Rathje, an archaeologist at Stanford University in California who has excavated many landfills. “The preservation of things is really pretty amazing. We think of artefacts as being so impermanent, but in certain cases things are going to last a long time.”

Ocean sediment cores will show a brief period during which massive amounts of heavy metals such as mercury were deposited, a relic of our fleeting industrial society. The same sediment band will also show a concentration of radioactive isotopes left by reactor meltdowns after our disappearance. The atmosphere will bear traces of a few gases that don’t occur in nature, especially perfluorocarbons such as CF4, which have a half-life of tens of thousands of years. Finally a brief, century-long pulse of radio waves will forever radiate out across the galaxy and beyond, proof – for anything that cares and is able to listen – that we once had something to say and a way to say it.

But these will be flimsy souvenirs, almost pathetic reminders of a civilisation that once thought itself the pinnacle of achievement. Within a few million years, erosion and possibly another ice age or two will have obliterated most of even these faint traces. If another intelligent species ever evolves on the Earth – and that is by no means certain, given how long life flourished before we came along – it may well have no inkling that we were ever here save for a few peculiar fossils and ossified relics. The humbling – and perversely comforting – reality is that the Earth will forget us remarkably quickly.

Personally, I prefer to imagine a world without idiots like these people.