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While there is a nice webcomic with a similar theme, I'm talking about a hopefully more reliable claim: The Science of Discworld alternates between chapters written by fantasy author Terry Pratchett about the fantasy setting of the Discworld's wizards having (accidentally) created Earth inside a glass bowl and observing its evolution fast forwarded, and chapters written by mathematician Ian Stewart and biologist Jack Cohen trying to elaborate on the scientific part of the respective epoch.

Now while one of the fantasy chapters describes a pre-human (in fact, some large lizards, you know, dinosaurs) civilization that is then extinguished by a meteor (and was made-up for all we know), the following scientific chapter states the following (bold emphasis mine):

In order not to mislead you, we should point out at once that there is no scientific evidence for the existence of any dinosaur civ­ilization, no matter what events are going on in the Roundworld Project. But... whenever a scientist says 'there is no scientific evi­dence for', there are three important questions you should ask -especially if it's a government scientist. These are: 'Is there any evi­dence against?, 'Has anyone looked?', and 'If they did, would they expect to find anything?'

The answers here are 'no,' 'no', and 'no'. Deep Time hides a lot, especially when it's assisted by continental movement, the bulldoz­ing ice sheets, volcanic action and the occasional doomed asteroid. There are few surviving human artefacts more than ten thousand years old, and if we died out today, the only evidence of our civi­lization that might survive for a million years would be a few dead probes in deep space and various bits of debris on the Moon. Sixty-five million? Not a chance. So although a dinosaurian civilization is pure fantasy, or, rather, pure speculation, we can't rule it out absolutely. As for dinosaurs who were sufficiently advanced to use tools, herd other dinosaurs ... well, Deep Time would wash over them without a ripple.

So, is that true? Would the civilization of mankind, once perished for a million years, leave no traces more noticeable than the dinosaurs' bones are to us nowadays?

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Tobias Kienzler
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  • That's because, as Russell would say, the philosophic burden of proof lies upon a person making scientifically unfalsifiable claims. See the Russel's teapot. Or, to make it simplier, there is any evidence against the mostly invisible, impalpable giant dragon residing in my garden that only I can see? Has anyone looked? If you did, would you expect to find anything? – Duralumin Jul 26 '13 at 14:39
  • True, maybe I should put focus on the second part, i.e. whether human civilization in its current state would leave enough traces to prove its existence in a million years – Tobias Kienzler Jul 26 '13 at 14:41
  • Are we talking traces on the Earth itself, or would traces off-planet be allowed? – rjzii Jul 26 '13 at 14:42
  • @rob Well, any traces that are sufficiently likely to be noticeable by a civilization as "advanced" as we (think we) are - are you suggesting Neil's footsteps would still be there? – Tobias Kienzler Jul 26 '13 at 14:43
  • I remember seeing an article a while back about how long man-made objects on the moon would last and they included speculation on the foot prints as well. The moon is fairly inert - barring rocks hitting it - so things can last a long time up there. However, it's also hard to get there to actually find stuff which factors in as well. "[The Mote in God's Eye](http://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye)" touched upon this topic a bit as well in some ways. – rjzii Jul 26 '13 at 14:46
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    @Duralumin I think we can re-frame from the eye-rolling since deep time communications is also a [real present day problem](http://en.wikipedia.org/wiki/Human_Interference_Task_Force). Looking backwards is interesting way of examining the problem. – rjzii Jul 26 '13 at 14:48
  • @rob Interesting point, though I wonder how likely they'd be discovered, since apart from these little traces the moon is still quite barren... – Tobias Kienzler Jul 26 '13 at 14:50
  • @Rob.My fault,as I was hurrying (1).Truth be said, my reply was only concerned with the first half of the quote.And then, at the time, the question was different. Btw, I already knew of the Yucca Montain problem and the Human Interference TF. Concluding, all the above amounts to me making a comment and not an answer. (1) Sleep deprived, hot, tired and in hurry, in fact. – Duralumin Jul 26 '13 at 15:39
  • Ceramics could last that long if that happened to avoid sufficient crushing/grinding action. But over that time-scale there are few starting locations that would qualify. Lacking any other basis for evaluation I would guess the odds are similar to those for fossilization of bony body parts. – dmckee --- ex-moderator kitten Jul 26 '13 at 16:43
  • Please use comments for asking clarification, or suggesting improvement. General discussion and speculation should happen in chat. –  Jul 26 '13 at 17:13
  • I would expect that there would be some traces, but they might not be obvious. I would expect that one thing that might be seen would be the remains of roadcuts and the like. they would fill with dirt but still be visible as very linear features – Zachary K Jul 29 '13 at 07:20
  • If the earth were to survive that long, all the rocks from human times would be full of fossil and chemical traces 3-5 billion years from now. seeing how old stromatoliths are, and how much more we leave than they did. – bandybabboon Dec 07 '14 at 12:46

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The concept of the "anthropocene" answers your question.

See

The term was coined "because a growing number of geologists think that human activity is having such an impact on our world that we're inaugurating a new geological interval. It's signature will be detectable many millions of years from now." (Quirks and Quarks)

Proposed marks we'll leave in the geological record:

  • A "building" strata: the materials that makes up our cities will add an identifiable strata to the record in the right parts of Earth (Quirks)
  • Sea level increases will cover red soils with black mud (Quirks)
  • Changes to the isotopic composition of soils reflecting environmental change (Quirks)
  • Plastic (Quirks)
  • Biostratigraphic changes: changes in distributions of animal fossils due to climate-caused migration, extinctions, and physical translocation of species by humans
  • Increased acidity in the oceans will cause reef coral deaths, and will dissolve away lime sediments (this type of effect is quite clear in previous global warming periods) (Quirks)

The impact that humanity has had is geologically quite abrupt, and may be difficult to distinguish from a meteorite impact. (Quirks)

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    Actually shouldn’t plastic completely decompose in a few millennia? – Konrad Rudolph Jul 27 '13 at 15:27
  • @KonradRudolph Some types will, in sunlight. –  Jul 27 '13 at 16:00
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    Hm, that last paragraph makes me wonder: Is there any way to prove the Dinosaurs didn't have a civilization at the end but managed to nuke themselves? Not that I consider that seriously, but still... – Tobias Kienzler Jul 29 '13 at 07:50
  • @TobiasKienzler That's a discussion for [chat](http://chat.stackexchange.com/rooms/311/hub-of-reason). –  Jul 29 '13 at 12:08
  • What about underground craters from nuclear tests in Nevada? Although the radiation may be gone (Plutonium-239 has a half-life of 24,400 years), I would think the blast cavity, with rock subjected briefly to millions of degrees, would obviously be seen as not naturally formed. Then there are nuclear waste facilities (or will be), which presumably will have measurable radiation: TC-99 (half life 220,000 years), I-129 (half-life 15.7 million years), Np-237 (half-life 2 million years), and Pu-239, already mentioned. – tcrosley Dec 07 '14 at 17:40
  • That last bullet should go, if natural warming did the same thing then that would only prove the earth warmed, not that intelligent beings were able to cause it. – Andy Dec 13 '14 at 18:57
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    @tcrosley its been speculated that there have been natural fission reactions in the earth past. http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor – Andy Dec 13 '14 at 18:58