Long term evidence of civilization.

[xilman]

Originally Posted by rogue

IS INTELLIGENCE COMMON OR RARE IN THE UNIVERSE?

That article contains the statement "This result stems from humanity’s relatively late appearance in Earth’s habitable window, suggesting that its development was neither an easy nor ensured process.

"Its" in this context refers to intelligence.

Two things instantly stand out to me. First, humanity is not the only intelligent species on the planet, though it is undoubtedly the one with the greatest technological prowess. A number of cephalopods, birds and other mammals show remarkably intelligent behaviour, including the use of technology.

Second, I do not know of any concrete evidence that indicates highly intelligent species did not evolve before us. There is good evidence that they did not use a large amount of coal as a significant source of energy, but that's about it. As recently as 500 years ago we didn't use coal in any significant quantity yet few would deny that H. sap. was intelligent at that date.

Give it another 100M years and I suspect that the only clear evidence for our technological civilization will be geological evidence of a simultaneous and sudden increase in atmospheric CO₂ levels, a mass extinction event, and a global distribution of wheat, rice and maize pollen. Even those signals would be hotly debated.

If the future paleontologists get very lucky, they might find fossil graveyards containing carefully arranged human skeletons and they might find cleanly sawn bones of fodder animals --- which would indicate intelligence and at least limited technology. They would have to get very lucky indeed to find, say, titanium bone implants which would be a dead giveaway for high technology. IMO, our presence would be more likely first be discovered on the moon. We haven't yet explored the moon in any detail so have no idea whether buried and/or meteor-battered artefacts are to be found there.

[retina]

Originally Posted by xilman

Give it another 100M years and I suspect that the only clear evidence for our technological civilization will be geological evidence of a simultaneous and sudden increase in atmospheric CO₂ levels, a mass extinction event, and a global distribution of wheat, rice and maize pollen. Even those signals would be hotly debated.

Things like the pyramids and underground nuclear bunkers etc. will leave traces of their existence IMO. Concentrations of metals, like rods of iron encased in concrete for example, will be heavily corroded but still recognisable in some favourable locations and easily judged as as not natural.

Digital evidence survival would likely require a continuous lineage of intelligence to keep it fresh on new media periodically. But I see no reason why we would expect a break in lineage. Being intelligent and selfish "we" would find ways to keep ourselves going, gradually changing as time passes, but able to preserve various things from our heritage we judged important, valuable or interesting.

[xilman]

Originally Posted by retina

Things like the pyramids and underground nuclear bunkers etc. will leave traces of their existence IMO. Concentrations of metals, like rods of iron encased in concrete for example, will be heavily corroded but still recognisable in some favourable locations and easily judged as as not natural.

Digital evidence survival would likely require a continuous lineage of intelligence to keep it fresh on new media periodically. But I see no reason why we would expect a break in lineage. Being intelligent and selfish "we" would find ways to keep ourselves going, gradually changing as time passes, but able to preserve various things from our heritage we judged important, valuable or interesting.

The pyramids, African and American, are already looking very much the worse for wear after < 5000 years. They will have weathered away completely long before 100M years are up. I suspect that any traces of them will be hard to find after as little as 100K years.

Concrete the same: most of it will be either weathered on the surface or dragged down a kilometer or more into hot wet acidic water (water *is* an acid remember) where it will be dissolved and dissipated.

The best chance for survival in the long term will be places like Amsterdam, New Orleans and Bangladesh --- burial in mud well away from volcanoes and subduction zones.

I have serious doubts as to our ability to keep our civilization and its records intact for another 10K years, let alone 100M. Consider what has been happening in Sumer and Akkad recently to see how records can be destroyed so easily.

One dead giveaway would be the chance discovery of the remains of a museum, with its collection of resilient minerals in close proximity and no obvious explanation for the variety of substances found there. The chances of one both surviving erosion and subsequently being discovered must be remote.

[Uncwilly]

Originally Posted by xilman

The pyramids, African and American, are already looking very much the worse for wear after < 5000 years. They will have weathered away completely long before 100M years are up. I suspect that any traces of them will be hard to find after as little as 100K years.

What have you against the Asian pyramids (ziggurats)?

[xilman]

Originally Posted by Uncwilly

What have you against the Asian pyramids (ziggurats)?

Nothing. Please apply Hanlon's Razor in this instance.

That said, they are much more eroded than their co-evals. Mesoamerican pyramids are such recent constructions that it's hard to tell their longevity compared with the others. A good number of European cathedrals are of comparable age and in much better shape, by and large, despite their much more delicate construction. Only goes to show what a thousand years of maintenance can achieve.

[Uncwilly]

Originally Posted by xilman

Nothing. Please apply Hanlon's Razor in this instance.

Already had.

[ewmayer]

Originally Posted by rogue

Bumblebees bite plants to make them flower early, surprising scientists

Not sure why this would be surprising - flowering plants and their pollinators co-evolved over many millions of years, so it makes perfect sense for such a plant to wait for a clear sign of its pollinators being around before investing energy in flowers. This would help it to tailor its flowering time and vigor to variable end-of-winter times and natural events which affect the population of its pollinators, for example. Bumblebee populations crash due to, say, some kind of fungal pathogen or severe winter? Minimize investment in flowers until populations (hopefully) recover.

Originally Posted by xilman

Give it another 100M years and I suspect that the only clear evidence for our technological civilization will be geological evidence of a simultaneous and sudden increase in atmospheric CO₂ levels, a mass extinction event, and a global distribution of wheat, rice and maize pollen. Even those signals would be hotly debated.

You forgot forever chemicals ... and too busy to do the research just now, but I suspect there are some radionuclides produced in bomb tests and nuclear reactors with a suitably long half-life to leave distinctive isotopic signatures in the geologic record.

[Uncwilly]

Originally Posted by ewmayer

You forgot forever chemicals ...

Which ones? Put organics under heat and pressure and the forever chemicals will go away. If you don't think so, why aren't we looking in crude oil for markers of past civilizations?

[ewmayer]

Originally Posted by Uncwilly

Which ones? Put organics under heat and pressure and the forever chemicals will go away. If you don't think so, why aren't we looking in crude oil for markers of past civilizations?

You're thinking of e.g. subducting slabs of earth's crust ... I'm thinking of what the geologists call cratons, which can and have survived for billions of years subject only to sedimentation. Whence the heat/pressure needed to break C-F bonds there? Consider, say, the oldest strata exposed by the Colorado river bandsawing its way through the slowly rising geology around the Grand Canyon, for instance. Aside from weathering, what extremes (in the sense of being able to destabilize the aforementioned bond) have those rocks been exposed to between the time of their sedimentary formation and later exposure?

Also, while we may not be looking in crude oil for markers of past civilizations given the near-universal belief among scientists that such civilizations lacked the technology needed to influence the geological record in a way that might be show up in such parts of the earth, it is certainly possible that had such a civilization existed, it would leave chemical/radioisoptic markers such as I describe which would show up in oil. The fact that petrologists have found no such markers would simply confirm that no such civilization existed prior to ours.

Oh, I also forgot satellites in sufficiently high orbits. They would of course be dead signal-emission-wise, but the highly reflective ones might still show up they way they do now, easily visible to the naked eye and shapes discernible in high-resolution telescopes.

[xilman]

Originally Posted by ewmayer

Oh, I also forgot satellites in sufficiently high orbits. They would of course be dead signal-emission-wise, but the highly reflective ones might still show up they way they do now, easily visible to the naked eye and shapes discernible in high-resolution telescopes.

I don't have the time and knowledge yet to answer your chemical marker questions. However, I think you will find that high altitude orbits are unstable on timescales of a megayear or so due to planetary and (especially) lunar perturbations.

After a few megayears they will not be highly reflective. Proton and dust bombardment will see to that.

Anyway, even something which is highly reflective and in a high orbit is not easy to resolve. Easy exercise for the reader: calculate the angle subtended by a 1m object at a distance of 100,000 km. Then compute the aperture of a diffraction limited telescope working at 500nm wavelength required to produce an image of that object which is 2 pixels across.

In passing, your naked-eye acuity is quite phenomenal. Geostationary satellites tend to be 10th magnitude or fainter. They are at 40,000 km, highly reflective, and a few metres across.

[chris2be8]

Originally Posted by xilman

Give it another 100M years and I suspect that the only clear evidence for our technological civilization will be geological evidence of a simultaneous and sudden increase in atmospheric CO₂ levels, a mass extinction event, and a global distribution of wheat, rice and maize pollen. Even those signals would be hotly debated.

There would be a lot of evidence to find with a little care. Tunnels from mining etc would have collapsed but left traces in the rock. Remains of roads, buildings etc buried in sediment would be a lot easier to find than animal fossils.

Also the article said that life was probably common, but intelligent life rare. But we have no evidence of how common life is so it could easily be very rare for life to appear at all.

Chris