The Silurian Hypothesis

[Monoriu]

I find it extremely unlikely that an advanced civilization can leave absolutely no trace whatsoever. 

[Malthus]

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.

You didn't address the second link, which strongly raises the notion that "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" is incorrect, at least for some landscapes.

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

All it takes is *some* survivals to make a civilized past obvious.

No-one doubts that there is a huge turnover in landscape due to geologic forces. What is in question, that you have asserted as fact, is whether this turnover is so total and complete as to erase all traces of man-made landscape modification.

Consider that in the middle east, entire hills, known as "tels", are constructed out of human garbage; much of that long-lasting (worked stone, pottery sherds). These where made by relatively small-scale civilizations ...

[Malthus]

More of the same:

https://www.researchgate.net/publication/240798767_The_Enigma_of_Survival_Problems_Posed_by_Very_Old_Paleosurfaces

"Ancient Landscapes are also termed palaeosurfaces (e.g. Twidale 2000 Twidale , 2003 ). Some have experienced extremely prolonged sub-aerial exposure and are pre-Cenozoic. ..."

[Malthus]

Yet more:

More surprisingly, perhaps, landscapes of great antiquity that have not been preserved by burial and then resurrected, but which have apparently been exposed to the elements since inception, loom large in the landscape in several parts of the world. Michel
(1978) and Demangeot (1978) have recorded lateritised land surfaces of later Mesozoic age in W Africa and S India respectively, and King (1942, 1950) long ago presented cogent arguments pointing to the later Mesozoic age of the high plains and plateaux  bounded by the great Drakensberg Escarpment in S Africa. Similar discoveries have been made in Australia  ...

https://link.springer.com/article/10.1007/BF00214393

This means that, in various places across the world, surface landscapes have allegedly survived since the time of the dinosaurs.

The problem with the 'the entire surface of the world has been replaced, so nothing can have survived from then until now' is that it is based on an outdated notion of the uniformity of impact of geological forces. Certainly it is true that most places have been completely changed. However, most is not the same thing as all, and it appears that the weight of scientific evidence is against "all" having been changed.

[Barrister]

Thanks for replying to this Malthus!

I suspect though that both of us are going at it with our own biases of past experience: you go back to your archaeology roots talking about middle eastern tels, despite that being insignificant in geologic time frame.  And I probably look too much at my own background, which was indeed in geology (but totally unconcerned with any notion of looking for proof of civilizations).

I don't think we're going to be able to definitively solve this one though.  I would note that of your three links, two are paywalled, with only a brief synopsis available for public viewing.  The one that can be viewed (your first link) isn't any original research, but rather an analysis and summary of past research.  It also is quite upfront that this is quite an extraordinary and controversial claim that is being made: the title of the entire article is "The ancient landscapes concept: 'Important if true'".

So just two thoughts:

Even if true, such ancient landscapes are quite rare on the earth - limited to areas with little tectonic activity, unreactive and exposed bedrock, little exposure to water.  Indeed such landscapes might be limited to Australia alone.  As such, the fact we don't see any proof of prehistoric civilizations in some of the most inhospitable places on earth doesn't really tell us very much.

Second, it's still a matter of timeframe.  I was either using a timeframe of 50 million years, or going as far back as the start of the cretaceous period, 65 million years, as that seemed like a pretty far back period of time.  But the title of the thread itself is the Silurian Hypothesis - and the Silurian period is a whole order of magnitude further back, starting 444 million years ago, and ending 419 million years ago (and predates even the dinosaurs).  Even your "ancient landscapes" don't date that far back.

So I'm going to stick with my conclusion so far: prehistoric civilizations are extremely unlikely, but can not be entirely ruled out.

[Malthus]

Thanks for replying to this Malthus!

I suspect though that both of us are going at it with our own biases of past experience: you go back to your archaeology roots talking about middle eastern tels, despite that being insignificant in geologic time frame.  And I probably look too much at my own background, which was indeed in geology (but totally unconcerned with any notion of looking for proof of civilizations).

I don't think we're going to be able to definitively solve this one though.  I would note that of your three links, two are paywalled, with only a brief synopsis available for public viewing.  The one that can be viewed (your first link) isn't any original research, but rather an analysis and summary of past research.  It also is quite upfront that this is quite an extraordinary and controversial claim that is being made: the title of the entire article is "The ancient landscapes concept: 'Important if true'".

So just two thoughts:

Even if true, such ancient landscapes are quite rare on the earth - limited to areas with little tectonic activity, unreactive and exposed bedrock, little exposure to water.  Indeed such landscapes might be limited to Australia alone.  As such, the fact we don't see any proof of prehistoric civilizations in some of the most inhospitable places on earth doesn't really tell us very much.

Second, it's still a matter of timeframe.  I was either using a timeframe of 50 million years, or going as far back as the start of the cretaceous period, 65 million years, as that seemed like a pretty far back period of time.  But the title of the thread itself is the Silurian Hypothesis - and the Silurian period is a whole order of magnitude further back, starting 444 million years ago, and ending 419 million years ago (and predates even the dinosaurs).  Even your "ancient landscapes" don't date that far back.

So I'm going to stick with my conclusion so far: prehistoric civilizations are extremely unlikely, but can not be entirely ruled out.

I'm as hard on Australians as the next guy, but I still think of them as basically "civilized".  If humans can live on places like Australia, so too can our hypothetical pre-human civilizations. Indeed, humans are found in all sorts of horrible places, like the Atacama Desert:

https://en.wikipedia.org/wiki/Salta%E2%80%93Antofagasta_railway

Certainly landscapes such as those mentioned in the articles are not the common run, but allegedly (according to the last link) they exist in several places ... but really, all you need is some.

The issue isn't going to be whether how much survives, but whether anything survives. Finding even one obviously man-made relic (say, a straight cutting through bedrock) would give the game away.

Sure, if the point in time is far back enough, there would be no evidence surviving ... but that also makes any notion of intelligent beings increasingly absurd. Intelligent dinosaurs is much more possible than intelligent trilobites.  If intelligent dinosaurs created a civilization like ours, we'd certainly know about that; not so much if intelligent trilobites of the early Silurian created one - but that isn't very likely.

[alfred russel]

Also the earth is 4.5 billion years old. I know the proposal is for a more recent period, but what if there was an ancient civilization 2.5 billion years ago? That makes the challenge doubly difficult: 1) so much more time has past, and 2) the earth's environment was likely different enough to lead to an ancient civilization quite different from our own (and hence we may be oblivious to some signs).

[Barrister]

Also the earth is 4.5 billion years old. I know the proposal is for a more recent period, but what if there was an ancient civilization 2.5 billion years ago? That makes the challenge doubly difficult: 1) so much more time has past, and 2) the earth's environment was likely different enough to lead to an ancient civilization quite different from our own (and hence we may be oblivious to some signs).

Problem is 2.5 billion years ago there wasn't even any multi-cellular life on earth, and I'm not even sure there was much atmospheric oxygen.  Any civilization that long ago would have had to come from somewhere else.

[Malthus]

Also the earth is 4.5 billion years old. I know the proposal is for a more recent period, but what if there was an ancient civilization 2.5 billion years ago? That makes the challenge doubly difficult: 1) so much more time has past, and 2) the earth's environment was likely different enough to lead to an ancient civilization quite different from our own (and hence we may be oblivious to some signs).

If there was, it wasn't terrestrial in origin. 2.5 billion years ago, the most advanced life on Earth was probably a multicellular cyanobacterium:

http://www.bbc.com/earth/story/20150701-the-origin-of-the-air-we-breathe

Edit: holy simulpost Batman! 

[Josquius]

Also the earth is 4.5 billion years old. I know the proposal is for a more recent period, but what if there was an ancient civilization 2.5 billion years ago? That makes the challenge doubly difficult: 1) so much more time has past, and 2) the earth's environment was likely different enough to lead to an ancient civilization quite different from our own (and hence we may be oblivious to some signs).

Problem is 2.5 billion years ago there wasn't even any multi-cellular life on earth, and I'm not even sure there was much atmospheric oxygen.  Any civilization that long ago would have had to come from somewhere else.

Earth being seeded from elsewhere is quite a different awesome theory.

I also recall seeing a theory however that calculated due to the age of the universe we should be towards the earlier side of advanced life.

[Valmy]

Earth being seeded from elsewhere is quite a different awesome theory.

I also recall seeing a theory however that calculated due to the age of the universe we should be towards the earlier side of advanced life.

Maybe we are going to seed them!

[Malthus]

Earth being seeded from elsewhere is quite a different awesome theory.

I also recall seeing a theory however that calculated due to the age of the universe we should be towards the earlier side of advanced life.

Maybe we are going to seed them!

The hope of every R34 science fiction artist out there ... 

[Caliga]

I also recall seeing a theory however that calculated due to the age of the universe we should be towards the earlier side of advanced life.

Right, I've read that as well, in the context of "why haven't we heard from other civilizations?" (we're the first ones)

[Josquius]

Earth being seeded from elsewhere is quite a different awesome theory.

I also recall seeing a theory however that calculated due to the age of the universe we should be towards the earlier side of advanced life.

Maybe we are going to seed them!

That's my religious theory. That humans are life-sperm.

[alfred russel]

Also the earth is 4.5 billion years old. I know the proposal is for a more recent period, but what if there was an ancient civilization 2.5 billion years ago? That makes the challenge doubly difficult: 1) so much more time has past, and 2) the earth's environment was likely different enough to lead to an ancient civilization quite different from our own (and hence we may be oblivious to some signs).

Problem is 2.5 billion years ago there wasn't even any multi-cellular life on earth, and I'm not even sure there was much atmospheric oxygen.  Any civilization that long ago would have had to come from somewhere else.

You and Malthus are both completely missing the point....How can we be sure there wasn't multicellular life on earth 2.5 billion years ago?

I didn't pick that date at random. That is the date that atmospheric oxygen basically exploded.