The Silurian Hypothesis

[Caliga]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

65 million years later?

[Barrister]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

[Caliga]

Anyway, the dudes who authored the paper weren't pulling a Timmay; the discussion was initially about "if humans went extinct and aliens showed up in 100 million years could they tell we were ever here".  When they realized how difficult it would probably be for them to do so on such a massive timescale the second question came up of as an aside of "how do we know we've been the only civilization on earth?"

[The Minsky Moment]

Anyway, the dudes who authored the paper weren't pulling a Timmay; the discussion was initially about "if humans went extinct and aliens showed up in 100 million years could they tell we were ever here".

Twinkies

[crazy canuck]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

As Mongers pointed out, we have a pretty good fossil record with no signs of a civilization. 

[Malthus]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

Yet many rocks are completely unaffected, retaining even delicate fossils. Some areas (particularly, in the middle of continents) remain relatively unaffected, which is why we can even find some remains dating back hundreds of millions of years.

If we disappear from the earth, no doubt some of our works would disappear due to geological forces. But, of a certainty, not *all* of them. Our highways and railway cuttings crisscross whole continents. No known geological force would get rid of *all* cuttings we have made straight through bedrock; civilized agency would, I think, be obvious when such things are spotted.

[Malthus]

Anyway, the dudes who authored the paper weren't pulling a Timmay; the discussion was initially about "if humans went extinct and aliens showed up in 100 million years could they tell we were ever here".  When they realized how difficult it would probably be for them to do so on such a massive timescale the second question came up of as an aside of "how do we know we've been the only civilization on earth?"

The answer, though, is that the aliens likely could, and probably without even landing: find a straight line cut through (say) the Canadian Shield, as many are (railways and highways), and they would know.

[Barrister]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

As Mongers pointed out, we have a pretty good fossil record with no signs of a civilization.

As I pointed out, we don't have a very good fossil record.  Take a dinosaur like therizinosaurus - it's kind of famous because of it's extremely long claws, but it's only known from a couple of partial fossil remains - we don't even know what kind of head it had. 

And the dinosaurs existed for over one hundred million years - lots of time to leave fossils.  Human civilization has been around for what - 5,000 years?  And advanced technology only for 100-200 years.

I agree it's extremely unlikely, but the concept isn't quite so insane as you might think.

[Berkut]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

As Mongers pointed out, we have a pretty good fossil record with no signs of a civilization.

As I pointed out, we don't have a very good fossil record.  Take a dinosaur like therizinosaurus - it's kind of famous because of it's extremely long claws, but it's only known from a couple of partial fossil remains - we don't even know what kind of head it had. 

And the dinosaurs existed for over one hundred million years - lots of time to leave fossils.  Human civilization has been around for what - 5,000 years?  And advanced technology only for 100-200 years.

I agree it's extremely unlikely, but the concept isn't quite so insane as you might think.

On the other hand, the dinos were around a lot longer, but were probably not nearly as numerous as we are, AND had not artifical impact on their environment.

I think one argument against is that we seem to have a pretty decent, broad strokes sort of idea on how human level intelligence evolved throughout earths history. To imagine another intelligent civilization, don't we have to image some kind of offshoot from the eveolutionary tree that advanced MUCH faster than we think to intelligence, then died out...and we cannot see that in the evolutionary record? Genuine question here.

[Barrister]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

Yet many rocks are completely unaffected, retaining even delicate fossils. Some areas (particularly, in the middle of continents) remain relatively unaffected, which is why we can even find some remains dating back hundreds of millions of years.

If we disappear from the earth, no doubt some of our works would disappear due to geological forces. But, of a certainty, not *all* of them. Our highways and railway cuttings crisscross whole continents. No known geological force would get rid of *all* cuttings we have made straight through bedrock; civilized agency would, I think, be obvious when such things are spotted.

You're just missing how long a time frame you're talking about.

The Canadian shield is billion year old rocks.  But they haven't just been sitting there unaltered for a billion years.  They were covered up with new rock layers, then those rock layers eroded away leaving us with the Canadian shield.

In 50 million years the Canadian shield could be covered up with entire new geologic formations, or alternatively it could be uplifted and the shield would be eroded further down.

Heck you don't even have to go that far out - another round of continental glaciation would be enough to remove all trace of human civilization anywhere glaciers would cover, and that would take orders of magnitude less time.

I remember doing field work in northern manitoba the summer before law school with Manitoba Energy & Mines.  The particular formation we were working on, for some reason the geologist had commented that this was probably the base of mountain at one point.  Of course there was no mountain there now...

[Barrister]

On the other hand, the dinos were around a lot longer, but were probably not nearly as numerous as we are, AND had not artifical impact on their environment.

I think one argument against is that we seem to have a pretty decent, broad strokes sort of idea on how human level intelligence evolved throughout earths history. To imagine another intelligent civilization, don't we have to image some kind of offshoot from the eveolutionary tree that advanced MUCH faster than we think to intelligence, then died out...and we cannot see that in the evolutionary record? Genuine question here.

Well homo sapiens first showed up on the scene 300,000 years ago, and homo erectus about 1.5 million years ago.  That's pretty fast.  And despite that being very recent geologically speaking we don't have a great fossil record of human evolution either - missing links and all.

So we're hypothesizing a species that evolved and existed for a 1 or 2 million year period.  For all but the last few thousand years of that period though it could easily have been restricted to a fairly small geographic area, much like early humans in east Africa.  It could be that any fossils from that period have been eroded away, or alternatively still exist but buried under 100s of metres of rock.

[Malthus]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

Yet many rocks are completely unaffected, retaining even delicate fossils. Some areas (particularly, in the middle of continents) remain relatively unaffected, which is why we can even find some remains dating back hundreds of millions of years.

If we disappear from the earth, no doubt some of our works would disappear due to geological forces. But, of a certainty, not *all* of them. Our highways and railway cuttings crisscross whole continents. No known geological force would get rid of *all* cuttings we have made straight through bedrock; civilized agency would, I think, be obvious when such things are spotted.

You're just missing how long a time frame you're talking about.

The Canadian shield is billion year old rocks.  But they haven't just been sitting there unaltered for a billion years.  They were covered up with new rock layers, then those rock layers eroded away leaving us with the Canadian shield.

In 50 million years the Canadian shield could be covered up with entire new geologic formations, or alternatively it could be uplifted and the shield would be eroded further down.

Heck you don't even have to go that far out - another round of continental glaciation would be enough to remove all trace of human civilization anywhere glaciers would cover, and that would take orders of magnitude less time.

I remember doing field work in northern manitoba the summer before law school with Manitoba Energy & Mines.  The particular formation we were working on, for some reason the geologist had commented that this was probably the base of mountain at one point.  Of course there was no mountain there now...

The point you are missing is that, while this is no doubt true of *some places* which will be altered beyond recognition, it is not true of *every place*. Yet human activity spans most of the globe.

99% of that activity could be wiped out by glaciation or whatever, but all it takes is *one* mine in solid rock, *one* railway cutting through solid rock to visibly survive *anywhere on Earth*, and your hypothetical aliens would *know for sure* that some civilization had once existed.

The Appalachian mountains, for example are very old - 480 million years old - they were around when the dinosaurs were, and they are still around now, though much uplifted and eroded.

Even better, note how ancient survivals are found in Australia:

https://journals.openedition.org/geomorphologie/9166

But for almost a century, in Australia and elsewhere, there have been reports and claims of substantial landscape elements that are of much greater antiquity, and that, indeed, date from the Mesozoic (Twidale, 2007). They are not exhumed though such forms, which are of various ages, are recorded in the landscape and in the literature. Many are of subCretaceous date, but a few are as old as Archaean. The very old surfaces considered here are of etch type. Even duricrust-capped surfaces lack an A-horizon. Their character was concisely expressed by E.S. Hills when discussing the high plains of eastern Victoria: 'While these high surfaces of low relief clearly represent preserved relics of old surfaces which have escaped deep dissection, they have naturally suffered some reduction and modification in detail during the long periods of time to which they have been exposed to weathering and erosion, but this is relatively minor.' (Hills, 1975, p. 300).

[crazy canuck]

If they were anything like us, they would have altered the landscape in easily-recognizable ways - for example, highway cuttings through solid bedrock. These would still be visible millions of years later.

The time scale involved is enough for substantial continental drift.  Entire mountain ranges can form, or be eroded into nothingness.

As Mongers pointed out, we have a pretty good fossil record with no signs of a civilization.

As I pointed out, we don't have a very good fossil record.  Take a dinosaur like therizinosaurus - it's kind of famous because of it's extremely long claws, but it's only known from a couple of partial fossil remains - we don't even know what kind of head it had. 

And the dinosaurs existed for over one hundred million years - lots of time to leave fossils.  Human civilization has been around for what - 5,000 years?  And advanced technology only for 100-200 years.

I agree it's extremely unlikely, but the concept isn't quite so insane as you might think.

Your argument that there may be some specific fossils missing from the fossil record does not address the fact that there are no signs in any of the fossil record we do have.  For the theory to work there would have to be some as yet unexplored fossil lawyer in which the civilization is waiting to be discovered.  Not some detail within well explored fossil layers. 

To put it another way, there has been absolutely no signs of civilization in any of the context in which the numerous fossils we have were found.

[Barrister]

The point you are missing is that, while this is no doubt true of *some places* which will be altered beyond recognition, it is not true of *every place*. Yet human activity spans most of the globe.

99% of that activity could be wiped out by glaciation or whatever, but all it takes is *one* mine in solid rock, *one* railway cutting through solid rock to visibly survive *anywhere on Earth*, and your hypothetical aliens would *know for sure* that some civilization had once existed.

The Appalachian mountains, for example are very old - 480 million years old - they were around when the dinosaurs were, and they are still around now, though much uplifted and eroded.

https://geomaps.wr.usgs.gov/parks/province/appalach.html

The appalachians are indeed very old.  But not really that old.  From your link:

During the middle Ordovician Period (about 440-480 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event (Taconic orogeny) in North America. The once quiet, Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the birth of this new subduction zone, the early Appalachians were born.

Along the continental margin, volcanoes grew, coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.

Folded rocks in the Appalachians   
NASA image of the Appalachian Valley and Ridge province. These rock layers were folded during the series of continental collisions that formed the Appalachians during the Paleozoic Era. Much more recent (Cenozoic) uplift and erosion produced the landscape we see today.

So what happened 480 million years ago was that there began an active plate margin.  The Appalachians we see today though have been formed in the Cenozoic - the era we are in now, and the one that followed the dinosaurs.

So while there was mountain building in the past in the region, which formed some of the intense folding and metamorphosis we see in the rock layers, the Appalachian mountains were uplifted, and then eroded into the very old mountains we see today, all within the last 65 million years.

The entire surface of the earth would be turned over in 50 million years.  Nothing on the surface would be remaining as it is now.  100 or 1000 years?  For sure.  50 million - nope.

The problem with the Silurian hypothesis is surely something from this ancient race would have been fossilized - buried under rock and preserved.  It's not impossible that such fossils exist and just haven't been found, but pretty darn unlikely.

[Razgovory]

The surface will be different, but that means areas that get covered up will sometimes be pushed back to the surface.  That's how we find ancient fossils. You probably wouldn't be able to see it from space but you would be able to find uncovered layers that include modern roads.  Still I like my idea of looking sedimentary rock.  You can find that relatively easily.  You can find the boundary that that separate the Cretaceous and the Paleogene all over the world.  And in that boundary you can find you can find anomalous elements like iridium.  That's how we know a big space rock crashed into the Earth 65 million years ago.