[Vince Mills]

Vince Mills asked the Naked Scientists:
   
If man disappeared overnight, how long would it take nature to remove all traces of evidence of human civilisation?

Eg how long for all roads to be covered, buildings to decay to dust, metalwork to rust away etc etc

Vince Mills
(Solihull, West Midlands)

What do you think?

[imatfaal]

I guess some of the longest lasting effects might be those we are least proud of; anthropogenic climate change, desertification, island extinctions.  It will be a very long time before the build-up of radioactive materials in certain storage areas could be mistaken for natural occurrences.

On a less pessimistic note; I think the pure gold jewellery will remain for many many years.  Perhaps in the far distant future, when an alien civilisation is picking over the remains of earth, our cultures will be represented by tiny scraps of gold jewellery ranging from the ancient Egyptian through to the modern day.  Might not be the worst way to be memorialised...

[RD]

Why think of such a thing ?

(Solihull, West Midlands)

Now I get it  []

... our cultures will be represented by tiny scraps of gold jewellery ... Might not be the worst way to be memorialised...

But just think of all the sovereign rings  [xx(]

[Bored chemist]

It would be a long while before the evidence of our nuclear reactors disappeared.

[imatfaal]

Why think of such a thing ?

(Solihull, West Midlands)

Now I get it  []

very cruel - very funny

... our cultures will be represented by tiny scraps of gold jewellery ... Might not be the worst way to be memorialised...

But just think of all the sovereign rings  [xx(]

I dunno RD - I reckon some of the stuff they pretend is gold to sell to the sovereign wearers will have the life expenctancy of an M&S prawn sandwich - which eventually will leave just the sovereign which isn't that bad

[CliffordK]

There was a TV special on this recently.

The two Pioneer Probes have already shut down...  The Voyager probes will likely run out of power in a couple of decades and shut down.  However, it is likely that they could continue out into space for a very long time.  However, if we considered a close encounter with a similar probe...  if it passed beyond our heliosphere, we would never see it, and couldn't catch it even if we detected it.  If it passed beyond Jupiter's orbit, we also would likely never see it...  so it is unlikely they will ever be found.

On the scale of a few hundred years, a lot would remain, although cities would crumble, vehicles would rust, etc.  Deserts may preserve some things from rusting, but have their own consequences.

On a scale of a few thousand years, The great Egyptian Pyramids would likely still be there...
Cities would be swallowed up.

On a scale of a few million years.  Very little will remain on the surface of the planet.  Some buildings and other artifacts will undoubtedly sink or be buried, and essentially become fossilized. 

There certainly could be a unique biodiversity signature of our influence.  I.E.  Species that we've transported to obscure corners of the planet.

As mentioned, things like the Fort Knox vault will be very long lived.

As far as things like CO₂ levels.  A pulse of high concentrations might be seen in the Antarctic Ice Sheets for a very long time.  However, much of it will get absorbed in the ocean, and the planet will eventually reach a new equilibrium.  Future plant growth, death, and burying of carbon in the oceans and other areas will eventually bring the earth back to the cusp of a critical shortage of Carbon Dioxide.

[yor_on]

well, some of the stuff we leave after us will stay for a very long time. "Plutonium 239 has a half-life of approximately 24,000 years. That means that after 24,000 years half of the radioactivity contained in the plutonium will have decayed. However, the hazardous life of radioactive waste is at least ten times the half-life, therefore these wastes will have to be isolated from the environment for 240,000."

And "nuclear waste should be considered dangerous until it is no more radioactive than naturally occurring uranium ore, which is 6,000,000 years." We've made some stuff I think engraved in gold? Don't know how long that will last, and then you have cut diamonds of course. They will stay 'for ever' if you trust the commercials

But I would say the most part of modern society should disappear in a hundred years, with some parts surviving for thousands, like the pyramids. Just a guess though.

==

ah I was thinking of the landscape there, when it comes to houses? And asphalt?
Asphalt roads maybe a hundred years, maybe shorter. Nature grows fast.
City's? Those houses built in stone should last the longest I guess?
We've found Concrete aqueducts from the Roman time in Egypt if I remember right?
So?

All in all, give it three hundred years, then see if you recognize anything
 

[imatfaal]

Yoron - Stone henge has already been there 4500 years, and I cannot see much getting rid of it in three hundred years.

 [ Invalid Attachment ]

[yor_on]

Yeah, that one will be there for a l00Oongest time.

[CliffordK]

And asphalt?  Asphalt roads maybe a hundred years, maybe shorter.

I'm not sure about Asphalt. 
I've seen abandoned roads.  They decay quickly.  The vegetation certainly takes over within a few decades.  But you're right...  perhaps after 100 years or so most of the asphalt would be broken up.  Perhaps a little longer for reinforced concrete roadbeds.

Roadcuts might last longer though. 
Some places where slides are prevalent, the road beds will be swept away.  But, in many places the levelling and roadcuts will endure long-term.  Animals frequently use human hiking trails, and once the deadly vehicles would be gone, it is likely they would adopt the roadbeds, and thus for decades, or perhaps even centuries, the animal trails would follow the old roads paths.

Truthfully, though, I can't imagine any catastrophe that could wipe out 100% of humanity any time in the near future.  A virulent virus would likely leave some isolated pockets of survivors that would build immunity.  Or, even with modern communication, undoubtedly there would be some islands that would enforce a strict quarantine until the disease passes. 

Nuclear Weapons?  I'm seeing many doubters that there would be a true "Nuclear Winter"...  and I'm still hoping we will eventually leave the possibility of a full scale nuclear war with "Mutually Assured Destruction" behind us.

Collision with an asteroid the size of our moon would be very unlikely.

Global Crop Failure due to Ice Age, Volcano, etc...  It could kill off billions...  but still would leave millions of survivors.  Of course, that could mean complete loss of urban centers.

[yor_on]

Yeah, we're just a passing thing I suspect in the history of Earth. Although?

Who knows

[damocles]

Is there still a large vault of gold ingots at Fort Knox? I would hazard a guess that that will be the longest lasting evidence of human presence. Unlikely to deteriorate or change very much over a few million years.

[yor_on]

Making those excavating it wonder how all that gold came to be in that geological formation perhaps. Creating theories of everything, aliens from space, etc

[damocles]

Making those excavating it wonder how all that gold came to be in that geological formation perhaps. Creating theories of everything, aliens from space, etc

Much what I had in mind!
More remarkable than the gold being in the wrong geological formation, though, would be its distribution in huge nuggets of similar size and most unusual shape.

[yor_on]

You could create a really cool, hardcore Science fiction from that idea Damocles
Reminding of the 'black cloud' by Hoyle or Stapeldon's  'last and first men'.