If man disappears tomorrow, do you expect to see herds of poodles roaming the plains?

I've long thought about this - what would the Earth like if we all just disappeared? How long would it take for the cities to disappear? What would be the last item that hinted at our brief presence on this planet?

Well, I think about it with a wee bit more science behind me after NewScientist published it's, Imagine Earth without people article. Key quotes include:

"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.

... there are few better ways to grasp just how utterly we dominate the surface of the Earth than to look at the distribution of artificial illumination. By some estimates, 85 per cent of the night sky above the European Union is light-polluted; in the US it is 62 per cent and in Japan 98.5 per cent. In some countries, including Germany, Austria, Belgium and the Netherlands, there is no longer any night sky untainted by light pollution.

"Pretty quickly - 24, maybe 48 hours - you'd start to see blackouts because of the lack of fuel added to power stations," ... 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 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.

... "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."

The lack of maintenance will have especially dramatic effects at the 430 or so nuclear power plants now operating worldwide. Nuclear waste already consigned to long-term storage in air-cooled metal and concrete casks should be fine ... Active reactors will not fare so well. As cooling water evaporates or leaks away, reactor cores are likely to catch fire or melt down, releasing large amounts of radiation. The effects of such releases, however, may be less dire than most people suppose.

... places where native forests have been replaced by plantations of a single tree species may take several generations of trees - several centuries - to work their way back to a natural state. The vast expanses of rice, wheat and maize that cover the world's grain belts may also take quite some time to revert to mostly native species.

Highly domesticated species such as cattle, dogs and wheat, the products of centuries of artificial selection and inbreeding, will probably evolve back towards hardier, less specialised forms through random breeding. "If man disappears tomorrow, do you expect to see herds of poodles roaming the plains?" asks Chesser ...

On the whole, though, a humanless Earth will likely be a safer place for threatened biodiversity. "I would expect the number of species that benefit to significantly exceed the number that suffer, at least globally," Wilcove says.

Long before any of this, however - in fact, the instant humans vanish from the Earth - pollutants will cease spewing from automobile tailpipes and the smokestacks and waste outlets of our factories. ...

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.

Most policy-makers fail to take this committed warming into account, says Gerald Meehl, a climate modeller at the National Center for Atmospheric Research, also in Boulder. "They think if it gets bad enough we'll just put the brakes on, but we can't just stop and expect everything to be OK, because we're already committed to this warming."

Yet if the aliens had good enough scientific tools they could still find a few hints of our presence. ... 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."

... 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.

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.

Fascinating - read the whole article for the detail