A rather gloomy thought I know … but should modern civilisation collapse, what, and for how long, would remains of our presence persist? I’m thinking of a scenario where in the future the current global civilisation collapses and humans are greatly reduced in numbers and returned to relying on subsistence farming in small isolated settlements, or perhaps even living a hunter-gatherer existence … or maybe even as a species becoming completely extinct within a few thousand years or so (let's keep the details of this demise deliberately vague). What would then remain to say we were once here?

The upper Palaeolithic art in the Lascaux, Chavet and other caves, having already survived for some 20,000-30,000 years will probably still be there in another 30,000 years from now, if not much longer. The Great Pyramid has been standing for some 4500 years and I imagine it will still be essentially there, albeit more eroded, in 5000 years time. Similarly some current constructions: dams, the deep foundations of sky-scrapers, nuclear power stations, and some other massive buildings, will probably last a good few thousand years. Transportation tunnels and mines, if cut through solid rock, I would also expect to last many thousands of years. And what about artefacts? Glass is fairly stable, so while cars, tin cans, and carrier bags will mostly have corroded away in about a century, dumps of bottles should be good for a few thousand years, as will the gold circuitry on computers and other abandoned electronic goods … but will it be recognised for what it once was?

So what other signs might future archaeologists be able to find to indicate our current civilisation, and how far into the future would these remains last? What might still be there after 1,000, 10,000, 100,000, or a million years?

Plastic - tons and tons of the stuff - and some of it would last for up to half a million years. Glass can theoretically last for a million but ironically stone tools will still be down there for any distant future archaeologists and in pretty much the same condition as we find them today.

Some of the most persistent artefacts might not be on Earth at all, short of a direct meteor strike the debris on the moon should stick around almost indefinitely with no atmosphere or bacteria to degrade them.

Good point about all the stuff on the Moon and Mars, I hadn't thought about that.

But plastics ... how long-lived are they really? As a materials' scientist I feel I should know the answer: I don't. But I do know that a huge range of different types of polymers are known to be susceptible to environmental degradation. Most plastics are in some way damaged by prolongued exposure to sunlight (UV), and many are badly degraded by oxidation and leaching, ie exposure to air and water.

In addition an increasing number of different types of plastic have now been shown to be susceptible to attack by a variety of yeasts, moulds and bacteria (eg. there are currently moulds munching their way, albeit slowly, through the silicone-rubber airlock seals on the international space station). Addmittedly such bacterial degradation is very slow and it represents a drop in the ocean in terms of reducing the billions of tons of plastic rubbish that has been dumped into the environment over the past 50 years, but then these plastic-consuming bugs have only had 50 years to evolve to exploit this new food source, so the rate of degradation may not remain as low as it is now.

There again we do know that some natural polymers can be very long-lived indeed, under the right conditions: collagen (in skin) can easily last for a few thousand years if kept cool, dry and dark; keratin (hair and horn) can last for many tens of thousands of years; while amber (fossil tree sap) might be many tens of millions of years old yet still preserve the delicate keratin bodies of any entrapped insects.

However, leave an entire animal carcass exposed in a field and the whole thing will essentially be completely gone - flesh, hide, hair, horns and bones - within a decade.

A decade, that's 10 years. But it does explain why I never did got my promised new Game Boy from Santa in 2005 ... and also why I haven't received a single Christmas present since. So I guess Santa was shot down somewhere over Iraq or Syria in 2005, probably for intruding into "friendly" airspace. Poor Rudolph ... well, and poor Prancer, Dancer, Donner, Blitzen and the others too...

But I'm impressed by Rudolph's nose batteries ... still working after 10 years .... that's much, much better than my mobile phone!

ferval wrote:

Plastic - tons and tons of the stuff .....

Of course if we're talking rubbish dumps and pollution then there's also the unique human legacy of radioactive debris. Prior to 1945 (except in a couple of very unusual natural circumstances) many isotopic fission products can only be 'man-made'. The widespread initial 'spike' in these radioactive elements; whether in polar ice cores, deep sea alluvial cores, tree rings or just human and animal bones, does rather leave a indelible and worldwide marker that we were here. Indeed so globally ubiquitous is this initial marker (courtesy of atmospheric nuclear testing) that it has been suggested than this chemical signature be used as a universal start date (1945 AD) for the start of the new anthropocene geological epoch to coincide with the current on-going mass extinction event. So it would be a bit like the tell-tale global iridium spike as the marker for the K/T boundary about 67million years ago that marks the extinction of the (non-avian) dinosaurs.

Ah but will any future delver find the buried steps leading down to the great door, ajar and ravaged but still hanging from its rusted hinges, that leads to the great deserted halls of Res Historica? What would they make of the heap of decayed wood and corroded metal in the cellar?
"Is that - no it couldn't be - a trebuchet?"

Would the the sad little pile of fossilised bones be recognised as the remains of a pack of elite hunting meerkats? Might it be dry enough down there for some remnants of a collection of miffs, huffs and flounces to have survived?

And could they hear spectral voices, the distant echoes of laughter and animated discussion reverberating in the stillness?
"I wonder who lived here? And what happened to them?

Shaking their heads sadly, would they then climb back up into the light and pull closed the mighty doors with a mournful creak that sounds stangely like a whimper?

Meles meles wrote:

ferval wrote:

Plastic - tons and tons of the stuff .....

we're talking rubbish dumps

In  his 1991 book Generation X: Tales for an Accelerated Culture the Canadian novelist Douglas Coupland refers to 'dumpster clocking' which he defines as 'the tendency when looking at objects to guesstimate the amount of time they will take to eventually decompose'. He then gives an example:

"Ski boots are the worst. Solid plastic. They'll be around till the sun goes supernova."

An appropriate enough thought, perhaps, on today the Sun's birthday. If there is a general collapse of industrial civilisation then future generations of humans will no doubt mine and exploit the contents of our landfill sites as a wondrous resource. For a world without humans altogether, however, then in 2008 the History Channel produced a program called Life After People which considered just such a scenario. It can be viewed online here:

https://www.dailymotion.com/video/x1g5g09_life-after-people-episode-1-life-after-people-discovery-history-science-documentary_tv

It makes for disturbing yet compelling viewing.

Does silicon biodegrade easily? There will be an awful lot of female skeletons, plus silicon implants, to be dug up in future times. The bones will eventually disappear - will the implants? It's a grotesque thought and my bit of "erudition" (just for you, MM   ) this morning is to update Hamlet's comment to Yorick's skull: "Now get you to my lady's chamber and tell her, let her enhance her pretty dukkies to 38DD thick, to this favour she must come. Make her laugh at that."

Oh Temp, how I love the idea of future archaeologists scratching their chins and vigorously debating the ritual significance of the two deposits of silicon apparently placed on the chests of some female corpses - and a few male. Did they designate status or were they propitiatory gifts to their gods? Did they signify membership of a cult or maybe they were symbolic food for the afterlife journey - chicken fillets? Some future chemist will discover that once they were indeed soft and malleable, so what would they say when approached from a phenomenological perspective? Then of course, assuming they have understood the importance of silicon in other forms, chips principally, at around the same time, what conclusions might that prompt? How many PhDs might be written and how many learned papers published and careers made or destroyed? An even smaller sample would have two other deposits lying at the pelvic region - were these the high priestesses?
And then what about the false nails?

Shopping trolleys found imbedded in the crossing points of old water courses might lead to engaging conjecture.

Temperance wrote:

Does silicon biodegrade easily? There will be an awful lot of female skeletons, plus silicon implants, to be dug up in future times. Thxe bones will eventually disappear - will the implants?

I had no idea how stable silicones might, or not, be. Reading around on-line the consensus seems to be that .....

Silicones (ie the long-chain polymers based on repeated oxygen-silicon-oxygen units; as opposed to silicon, which is a hard brittle metalloid element with unique electrical properties; or silica, which is crystalline silicon dioxide, ie quartz) ... do seem to degrade when exposed to oxygen, sunlight, microbes in the soil, and particularly to cycles of leaching-drying, or freezing-thawing. So while the rates of degadation are generally quite slow, they certainly do degrade, either when exposed on the earth's surface or when buried in normal soil. In short, any breast implants or discarded flexible cake moulds can expect to be largely broken down by a combination of crystallisation, leaching, chemical and/or microbial attack, within a few hundred years ... or at least sufficiently so to be essentially unrecognisable as to their original physical form.

By contrast most shopping trolleys, being made from cheap, chrome-plated low-carbon steel, will largely have rusted away entirely within a century ... especially those that have been cast into rivers, ditches and canals as "votive offerings" to the great god Aldi. All that will be left after a hundred years will be the cupro-nickel pound coins still wedged in the plastic chain-lock, presumably put there, "to pay the ferryman".