Science Questions

How long would it take to wipe all trace of man from Earth?

Sun, 9th Nov 2008

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Question

Andy, King’s Lynn asked:

If the human race were to become extinct, how long before all traces of our existence were to disappear?

Answer

We put this to John Nudds, University of Manchester, Senior Lecturer in Palaeontology

The ParthenonThinking first in terms of archaeological timescale if the human race were to become extinct tomorrow then our buildings and roads would gradually decay and possibly within a hundred or hundreds of years many buildings would start to collapse. The sturdier stone built buildings would stand a lot longer than this as we know because we still have Greek Temples and Egyptian pyramids with us today. If we think in terms of those ancient civilisation sit will only be a few millennia before our city would firstly be overcome by vegetation and then would be buried by silt and sediment. If you consider the fabrics used in modern day construction: reinforced concrete, plastics etcetera these would certainly survive the burial for at least as long as the two million year-old stone tools dating from the early humans from Africa, for example. If we think in terms of a geological timescale – this country and indeed most of Europe has been under the sea for a much greater period of geological history than it has been land. The one thing we can be certain of is that sea levels will rise again and this country will be flooded once more by shallow sea and then all of our cities will become deeply buried by marine sediments. Over geological time, over millions of years they’ll be preserved in a rock stratum in just the same way that dinosaurs are preserved in rock strata from 65 million years ago.

When we consider that the oldest fossils we have on Earth are 3 and a half billion year-old single-celled microscopic, soft-bodied bacteria. If such tiny and delicate organisms can survive for that long then certainly the robust skeletons of Homo sapiens can survive for similar timescales. In actual fact organisms that live in the sea are much more likely to be fossilised than organisms like ourselves that live on land. So human fossils will always be rather scarce. We know this already because although hominids have been around for say five million years the actual numbers of fossil human skeletons is very low. Certainly some of us will be fossilised and we will survive buried in rock strata. To answer the question, when the human race does eventually become extinct, as it certainly will, although evidence of our existence will disappear from the Earth’s surface relatively quickly – say within a few millennia – evidence of our existence will survive buried at depth probably for as long as the planet survives.

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I would only say that I think it would be a whole lot quicker than might be invisaged by most. When nature is left to it's own devices, it can work pretty fast. To put an actual figure on the time, I wouldn't like to be so bold. I would guess the last things to be reclaimed by nature would be bank vaults.

Oh! and insurance policies. They are so tight fisted Don_1, Fri, 7th Nov 2008

My money is on coke bottles dropped on the continental slopes. They could last tens of millions of years easily and it wouldn't surprise me if they were there  billions of years later, if the rocks they are sitting in don't get destroyed. daveshorts, Fri, 7th Nov 2008

what about all the crap we have in space? at least some of it must be in a stable enough orbit to remain there a very long time, and then there's the moon landing site and the mars rover etc. Madidus_Scientia, Sat, 8th Nov 2008

Well that's easily taken care of. In about 5 billion years the Sun will begin to balloon into a red giant, engulfing all the inner rocky planets; that should be sufficient to sizzle into submission any surviving human remnants...

chris, Sat, 8th Nov 2008

so the answer is 5 billion years...


sit back and enjoy the ride. JnA, Sat, 8th Nov 2008

There is a book devoted to this very question, it's called "The World Without Us"
http://www.amazon.com/World-Without-Us-Alan-Weisman/dp/0312427905/ref=sr_1_1?ie=UTF8&s=books&qid=1226200600&sr=1-1

it's more poetic than you might think! franciscopereira, Sun, 9th Nov 2008

You would have done better to just tell us about the book or give a url to a synopsis or review of the book, instead your first post will be written off as spam and no one will buy it. Madidus_Scientia, Sun, 9th Nov 2008

Some aspects of this question (and that book) were already discussed here
http://www.thenakedscientists.com/forum/index.php?topic=13715.0 Bored chemist, Sun, 9th Nov 2008

I recently saw a History Channel documentary on this topic. It was very interesting.

http://www.history.com/minisites/life_after_people

decoy8888, Wed, 12th Nov 2008

human race disappearance from earth wouldnot be suddenly,but gradually.fertility of human will drop consistently,child birth will be very rare,population will less and less untill there is not enough people to maintain civilization.people will resident separately in several spot in world,have no contact each other,because there is not enough person to perate communication and traffic system.when the last person died ,human will diappear.this is a destiny.Any species has its lifespan,this is endowed by creater of the world. Paul first, Wed, 13th Jan 2010

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