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t0p
June 9th, 2013, 11:33 AM
I haven't seen the movie "After Earth" yet. But I was watching an advertisment for it on TV last night and it got me thinking: if the entire human race left earth right now (to live on another planet or whatever), what would the earth look like to our descendants if they decided to come have a look around in a thousand years time? What mark have we made that would still be distinguishable? And a back-up question: how long would it take for all marks of our civilisation(s) to be erased?

Cheesemill
June 9th, 2013, 12:32 PM
If we wait until the Long Now Foundation finish their clock before we leave then that will still be around in 10,000 years :)

http://longnow.org/clock/

SantaFe
June 9th, 2013, 12:56 PM
History Channel had a TV show based on that: http://www.history.com/shows/life-after-people

Was pretty good. ;)

deadflowr
June 9th, 2013, 05:25 PM
I too have only seen the ads, but I wonder if sabertooth tigers will really make a comeback.

t0p
June 9th, 2013, 08:13 PM
My (and your) Friend Google showed me this (http://discovermagazine.com/2005/feb/earth-without-people/).

Poor doggies. :(

TNFrank
June 9th, 2013, 08:18 PM
We saw the movie last weekend, pretty decent I though. I really don't think animals would change much in 1K years, there may be more of them or many less of them(man has done alot to bring the Whitetail Deer population back to numbers that are actually greater then it was before Europeans came to America) but I'm sure many momuments and stuff would stil be around. I mean look at Stonehenge or the Great Pyramids, they've been around for a few thousand years if not longer.

Max Blyss
June 9th, 2013, 08:29 PM
I think the rats would take over and evolve into a sentient, warlike species... They'd be like us except with pointier features and worse breath. Oh, and fur.

Copper Bezel
June 9th, 2013, 10:34 PM
Don't forget that we had fur until we became bipeds. The fact that we don't is an adaptation to heat loss for long-distance running, which bipedalism made possible for us, but most biped species do end up as runners, don't they? And you need grasping hands first, before the bipedalism, or the front limbs will just atrophy (T. rex rats!)

Generalist, rodent-like creatures are a good evolutionary starting point. The ancestor of all living mammals was similar, as was the first marsupial that colonized Australia and diversified into the marsupial wildlife we see there today. But that's without other mammals already filling all of those niches. For a mass extinction event, you'd expect the little rodent-like things to be the most likely to survive and also be the most suited to diversify into unoccupied niches, but just removing humans, who aren't in any particular competition with rodents now, wouldn't really change their opportunities all that much.

It's hard to imagine where sapience might evolve again, because it happened more or less by accident the first time - primarily a result of pressure for the parts of the brain involved in handling large social groups and the parts involved in toolmaking, I think. But I think the article's right that the first thing you'd see with the removal of humans would be the return of the large herbivores and their predators - we wiped those species out recently enough that even if we weren't exerting any pressure on those niches today, they still wouldn't have bounced back.

Really, next up for developing sapience might be the dolphins, if they're not there yet. = )

PJs Ronin
June 10th, 2013, 03:04 AM
Cockroaches and ivy will rule. Those two are indestructible.

QIII
June 10th, 2013, 03:08 AM
It used to be said that cockroaches and rats would survive a nuclear war.

The advice, then, was to get under your refrigerator if you saw a mushroom cloud.

Iowan
June 10th, 2013, 03:13 AM
It used to be said that cockroaches and rats would survive a nuclear war.

The advice, then, was to get under your refrigerator if you saw a mushroom cloud.But that's where the cockroaches and rats are...
OH! maybe that's why they survive.

QIII
June 10th, 2013, 03:15 AM
You dun caught on quick like fer an Iowegian.

jerryzambrano
June 10th, 2013, 06:04 AM
Nice question.
I've neither seen the movie or any of the ads/trailers/spoilers etc.
If we go by TV models such as "Revolution", the answer would be that it would take quite a while before we returned to a civilization as we know it.
However, there are other schools of thought (In the Sci-Fi world) that a new or fresh start on a distant planet would only encourage the rapid development of civilization as well as exceeding our previous understanding of it.

J.

Paqman
June 10th, 2013, 09:22 PM
What mark have we made that would still be distinguishable?

Depends how closely you looked. Most of what we build is steel and concrete, that will only last a few hundred or thousand years at the most. The sites of most cities would be overgrown and fairly hard to distinguish fairly quickly, although some in particularly dry environments would probably stay obvious for thousands of years. Ironically, probably some of the stuff from ancient civilisations (eg: the pyramids) would outlast a lot of modern stuff. Stone may be a poor building material in a lot of ways but it is just more stable than reinforced concrete.

Plenty of things would be fairly obvious if you looked close enough. Incongruous chemical signatures would be everywhere in the soil and to a lesser extent the air, and it would be pretty hard to explain the distribution of certain species without us as the vector (eg: the presence of rats and dogs or specific European species on remote Pacific islands)

There would be a few really obvious artefacts that were there to be found. In the US the monument Mount Rushmore is expected to last for many tens of thousands of years. It's in a fairly stable bit of geology and it's cut into granite, which is seriously hard. Should be there for any alien archaeologists even if we're long gone.

The longest lasting proof of our existence won't be on Earth though. The artefacts from the Apollo missions on the moon could well last for millions of years. Galvanic corrosion will eventually break down the technological components, but that could take a very, very long time. The moon isn't particularly geologically active, so the astronauts' footprints will stay exactly the same until something disturbs them, which might not be for many millions of years.

Moose
June 11th, 2013, 01:00 AM
History Channel had a TV show based on that: http://www.history.com/shows/life-after-people

Was pretty good. ;)

+1. I used to watch this show and it taught me a heap of interesting stuff. This show definitely comes close as to making assumptions of a post-humane world.

Copper Bezel
June 11th, 2013, 04:16 AM
Stone may be a poor building material in a lot of ways but it is just more stable than reinforced concrete.
The pyramids and other surviving megalithic constructions like that are also built with less of the dynamic tensions that decay could release. They're basically stacked on the ground. You couldn't well build a skyscraper out of stone, and a Great Pyramid made of reinforced concrete might outlast the original (although weathering would be a serious issue.) The fault tolerances when every square cm of ground is load-bearing seem rather higher. = )

llanitedave
June 11th, 2013, 04:21 AM
Depends how closely you looked. Most of what we build is steel and concrete, that will only last a few hundred or thousand years at the most. The sites of most cities would be overgrown and fairly hard to distinguish fairly quickly, although some in particularly dry environments would probably stay obvious for thousands of years. Ironically, probably some of the stuff from ancient civilisations (eg: the pyramids) would outlast a lot of modern stuff. Stone may be a poor building material in a lot of ways but it is just more stable than reinforced concrete.

Plenty of things would be fairly obvious if you looked close enough. Incongruous chemical signatures would be everywhere in the soil and to a lesser extent the air, and it would be pretty hard to explain the distribution of certain species without us as the vector (eg: the presence of rats and dogs or specific European species on remote Pacific islands)

There would be a few really obvious artefacts that were there to be found. In the US the monument Mount Rushmore is expected to last for many tens of thousands of years. It's in a fairly stable bit of geology and it's cut into granite, which is seriously hard. Should be there for any alien archaeologists even if we're long gone.

The longest lasting proof of our existence won't be on Earth though. The artefacts from the Apollo missions on the moon could well last for millions of years. Galvanic corrosion will eventually break down the technological components, but that could take a very, very long time. The moon isn't particularly geologically active, so the astronauts' footprints will stay exactly the same until something disturbs them, which might not be for many millions of years.

I agree with just about all of this. A thousand years is not very long in the overall scheme of things, biologically there'd be no perceptible evolution in the remaining species. As for the footprints on the Moon, they might not last all that long after all; there's a contant rain of micrometeoroids impacting the surface, and over the eons these should wear down and flatten out the astronaut's surface markings. The occasional larger impact will splatter glass over the top of them. Those same micrometeoroids will act like a super sand-blaster on the metal artifacts left behind, grinding them back into dust. That would almost certainly require millions of years, though.

deadflowr
June 11th, 2013, 04:35 AM
The moon isn't particularly geologically active, so the astronauts' footprints will stay exactly the same until something disturbs them, which might not be for many millions of years.

Or at least until Walmart opens up there.:)

philinux
June 11th, 2013, 12:55 PM
The film in question seems to have been panned by some critics. The audience seems split too. I'll wait till it arrives via my satellite dish or aerial.

http://www.rottentomatoes.com/m/after_earth/

On the question, the earth will return to being green and blue with fantastic views of the cosmos due to no artificial light.

Paqman
June 11th, 2013, 05:28 PM
The pyramids and other surviving megalithic constructions like that are also built with less of the dynamic tensions that decay could release. They're basically stacked on the ground. You couldn't well build a skyscraper out of stone, and a Great Pyramid made of reinforced concrete might outlast the original (although weathering would be a serious issue.) The fault tolerances when every square cm of ground is load-bearing seem rather higher. = )

Well the thing about stone is that you have to build with no tension at all. It's junk in tension, so you have to make sure it's subject to compressive forces only (which means minimising bending too).

A concrete pyramid wouldn't do as well as the real ones, concrete just insn't as stable chemically, and corrosion of the rebars would cause spalling. Not that you need rebars in a pyramid, you'd be better off using unreinforced concrete.

The Colosseum is made of concrete IIRC, so it can last a few centuries in reasonable shape.



As for the footprints on the Moon, they might not last all that long after all; there's a contant rain of micrometeoroids impacting the surface

Yeah, and the occasional big one. One near miss from a decent sized one could erase the footprints. Still an odd thought that something as normally transient as a footprint could be such an enduring artefact of our civilisation though.

I guess the gold record on the Voyager probes could last a long, long time though. Gold is super-stable, so that should last until it falls into a gravity well and gets swallowed. That could be a really long time.

TNFrank
June 11th, 2013, 07:44 PM
Nice question.

However, there are other schools of thought (In the Sci-Fi world) that a new or fresh start on a distant planet would only encourage the rapid development of civilization as well as exceeding our previous understanding of it.

J.

I don't know, have you watched "Firefly" lately? Plenty of em' live like they did in the 1850's, not all Hi-Tech like StarWars. Tech might be hard to come by on some of the outer planets, an ax and a gun might be your tools of choice in them parts, not a laptop and a phaser. ;)

llanitedave
June 11th, 2013, 09:19 PM
The chances of a distant planet being able to support human life without an already advanced technology are vanishingly small. Even if there's life already present, it would be life that evolved from scratch to be fine-tuned to that planet's conditions, and with enough degrees of freedom so that it's very likely quite different from our own biology in a chemical sense. It would have a different suite of proteins and amino acids, different sugars and fats, and quite possibly different nucleic acids (if indeed it even uses anything like DNA or RNA at all). It's not likely that we'd be able to eat it. It's also not likely that we'd be able to breathe the atmosphere. Even if there's oxygen, there might be a lot of other gases present that we don't handle well, but life on that planet does.

Similarly, alien invasion movies notwithstanding, life evolved on a different planet would probably have the same kind of issues with Earth.

PJs Ronin
June 12th, 2013, 03:41 AM
ruh roh... the roaches (http://news.discovery.com/tech/robotics/cyborg-cockroach-controlled-by-phone-130611.htm) are going cyborg.

Copper Bezel
June 12th, 2013, 03:42 AM
The chances of a distant planet being able to support human life without an already advanced technology are vanishingly small. Even if there's life already present, it would be life that evolved from scratch to be fine-tuned to that planet's conditions, and with enough degrees of freedom so that it's very likely quite different from our own biology in a chemical sense. It would have a different suite of proteins and amino acids, different sugars and fats, and quite possibly different nucleic acids (if indeed it even uses anything like DNA or RNA at all). It's not likely that we'd be able to eat it. It's also not likely that we'd be able to breathe the atmosphere. Even if there's oxygen, there might be a lot of other gases present that we don't handle well, but life on that planet does.
Firefly has an out due to a totally unexplained, rapid, and very effective terraforming technology (http://firefly.wikia.com/wiki/Terraforming) that's somehow easier than the next steps of building local infrastructure and cities. But yeah, that's not a thing that could happen in reality.

Paqman
June 12th, 2013, 03:21 PM
I suspect that in reality if humans ever do reach vaguely habitable worlds it'll be far easier and cheaper to solve the problem by manipulating our own biology to suit the new environment than any kind of mega-expensive planetwide geoengineering projects.

Better to modify ourselves to suit the new planet than try and modify and entire planet to suit us. At the very least some modifications for different gravity would seem the minimum, even if we were going to live in bubbles.

To my mind, if you're going to live in bubbles why bother doing it on a planet anyway? If we ever develop the technology to colonise the surface of an alien planet we would have developed the technology for permanent colonies in space long before. So why bother with the planets at all?

llanitedave
June 13th, 2013, 03:07 AM
You're singin' my song. I've been advocating for a long time that our future evolution and success lies among the water-rich asteroids and comets, not the surface of planets.

Asteroids and comets contain every element, and most compounds, essential to life. Those compounds they don't have can be synthesized easily. Their resources are accessible -- since they haven't undergone differentiation, their iron and precious metals will be mixed in with their carbon, hydrogen, and oxygen. In addition, much of this material will be reduced rather than oxidized, making processing easier. Very low gravity wells means that very little energy will be required to either arrive or depart -- goods manufactured there can be shipped elsewhere easily. (I didn't say shipment would be fast, only that it would be easy).

In order for all this to work, we'll need an economical and portable energy supply, almost certainly nuclear fusion. If we get that, our colonies/habitats will be self-sustaining, and we'll not only be able to exploit the asteroid belt, the Kuiper belt, and the Oort cloud, but we'll be able to easily slide out to the Oort clouds of nearby stars. Our descendants will not only be independent of Earth, they may forget they even originated there.

If we don't develop fusion successfully, we won't be going anywhere.

Paqman
June 14th, 2013, 09:59 PM
Exactly. For a space-faring civilisation, planets are the absolute worst places to visit. The gravity wells are just too big, making it obscenely expensive to go down or come up from them. Whatever it was down on the surface that you wanted would have to be something that couldn't be reached more cheaply and easily in space.

It's like they say, once you reach low Earth orbit you're half way to anywhere. So why would you put yourself right back at the bottom of that hole?

llanitedave
June 15th, 2013, 02:55 AM
Which is the real answer to Fermi's Paradox. The Alien's haven't visited us, because there's absolutely no advantage to them in doing so. It will be interesting to explore a few comets and see if they show any evidence of having been quarried.

Paqman
June 18th, 2013, 09:59 AM
Which is the real answer to Fermi's Paradox. The Alien's haven't visited us, because there's absolutely no advantage to them in doing so. It will be interesting to explore a few comets and see if they show any evidence of having been quarried.

Indeed, I'm also highly sceptical of the sci-fi vision of spacefaring civilisations flitting about between planets orbiting different suns. Since it seems like faster than light travel is in fact impossible and therefore long-distance interstellar travel is impractical I doubt we'll ever make physical contact with another species, especially when it's so much cheaper and easier to just send a beam of data.

Non-terrestrial habitats would have implications for SETI, but we mainly focus our gaze on stars not planets at present, and I think it's a reasonable assumption that most civilisations will still be clustered around stars (if only becuase that's where most of the interesting and useful stuff is in the universe). So we should pick up transmissions from ET if they were still reasonably close to the star we were listening to.

llanitedave
June 19th, 2013, 04:19 AM
I agree that civilizations would be concentrated near stars, even if they aren't planet-based. That's still where the resources are. It's likely to be a lot easier to find comet and asteroid-sized bodies orbiting a star than floating freely in space, even if there do happen to be trillions of "unaffiliated" small bodies.

Thing is, though, they'd be orbiting at a fairly large distance from that star, so you wouldn't have to dip too far into the gravity well. And since most stars are red and orange dwarfs, you can gain access to the great majority of the galaxy's resources without getting close to the radiation from the really energetic stars.