Here's a partial list of civilization ending events:
- Nearby supernovae
- Gamma ray bursts (eg from a neutron star that happens to be pointing directly at us and is sufficiently close)
- Large icy or rocky bodies hitting the planet
- Coronal mass ejections
- In about 1.6 billion years the increasing Solar output will make Earth uninhabitable
- In about 4 billion years the dying Sun will expand and essentially swallow the Earth, which will be long dead anyway
And here's a list of terretstial civilization killers:
- Supervolcanoes
- Climate change
- Global war
- Disease
- Ice ages
There are also others that we don't know how disruptive they will be other than probably super disruptive like the magnetic poles flipping (yes, this has happened at least 30 times).
My point here is that living on Earth is living on borrowed time. To survive in the really long term, we are going to have do something pretty drastic. Whatever we do (eg interstellar travel, moving the EArth--yes, this is possible) will require such massive energy expenditure that IMHO the only path forward will be to build a Dyson Swarm.
I'm also not yet convinced we can think of the time scales required to avoid our own destruction but at least, for a brief period of time, we will have created an awful lot of shareholder value.
Over sufficiently long time periods, all of these turn from an "if" into a "when".
This may sound positively retro and cold-warish, but IMO we've had way too many close calls in the 80 years nuclear weapons existed, and the quality of governance worldwide only seems to decline.
Neither the United States nor the Soviet Union treated each other with the vitriol that Russia and the US do today. Do you believe Putin and Trump are half the gentlemen Kennedy and Khrushchev were? I seriously believe we are closer now to nuclear deployment than at any time after 1945. During the Cuban Missile Crisis, Khrushchev was dreadfully worried about nuclear war and wrote many cables to Kennedy sorrowfully bemoaning the thought. While today, Putin airs propaganda to an increasingly uneducated audience treating a theoretical first nuclear use as unremarkable, and his ministers seem more concerned with the idea of whether or not they can ever beat MAD.[1] Trump liked to brag about the size of his "button" to Kim Jong Un like it was a WWE script. There's little hope I have that the world will escape, even a limited tactical deployment in the coming two decades, playing fiery chicken with the future of humanity.
Nuclear war is not an extinction event, though. Most people would survive, and while they would face hardships, the "radioactive wasteland" thing is a fairly sloppy sci-fi trope.
That aside, if all nukes were launched, it's not about the directly irradiated areas. Imagine how much fallout will be launched into the upper atmosphere when 10,000+ nukes hit, with many in the multi-megaton range.
The sheer amount of material thrown into the air could virtually blot out the sun for potentially years. Given that a large portion will be radioactive, it could be raining death for years too.
Ehh the dust will fall out of the atmosphere within a few months. Large population centers will be craters proba ly. The 4 year nuclear winter will cause starvation and eating the "long pork" such that up to 90% of the population globally will die.
Nice. Could a baseball pitched at 90% the speed of light from [anywhere that could produce such a speed] make it to Earth and impact? What can cause chunks of matter to travel this fast?
Could one make it to Earth and impact? The universe is very large, so it's a possibility, but space is very big and very empty, so we'd have to get very very very very unlucky for that to happen. But supernova explosions, pulsars and neutron stars, gamma-Ray bursts, supermassive black holes, and (theoretical) dark matter annihilation could all do it.
I wonder how often that happens. What's the fastest interstellar object we've ever detected? 0.01% of the speed of light, more or less? That's a few orders of magnitude shy of relativistic speed.
What is valuable life? What a philosophical question on HN! I think many will say "sentience". Many religious will say "if my religious leader said they are God's children". What is your definition?
> To survive in the really long term, we are going to have do something pretty drastic. Whatever we do (eg interstellar travel, moving the EArth--yes, this is possible)...
I'll bite. :-) Could you elaborate on what it might look like to transport the earth? Where would we move it to? How would life survive in transit without the sun?
There are different froms of this and it depends on your goal.
For the 1-5 billion year range your issue is the Earth overheating because Solar output is increasing by about 10% per billion years. There are three basic ways of doing this:
1. Putting something between the EArth and the Sun to reduce the amount of radiation that hits the Earth. This is by far the easiest;
2. Move the Earth to an orbit further from the Sun; or
3. Removing mass from the Sun to extend its life or reduce its output. This is the hardest.
So how do you move the Earth to a different orbit? Well that's pretty easy actually. I mean "easy" in the sense that it requires no new hypsics, no negative energy or negative mass. It just ruses gravity.
The Earth interacts with any mass. A sufficiently sized mass will attract the Earth. So you just fly large bodies of mass past the Earth to slowly nudge it in the direction you want. The Earth is relatively heavy (~10^24kg) so the energy requiremetns are still immense but it can be done slowly (and probably should be).
One proposal I've seen involves putting asteroids into an orbit such that their gravity pulls the Earth outwards a tiny bit each time they pass. Over an extended period of time (millions of years?) we could move the Earth outwards from the sun before the sun expands and cooks it. Obviously the Earth would pull the asteroid inward as well so we would have to adjust the asteroid's orbit after each pass. One proposal I've seen would be use Venus to keep the asteroid in a stable orbit. Essentially each pass of the Earth would slow the asteroid down a little bit, but each pass by Venus would speed it back up again, essentially pulling the Earth away from the sun while pulling Venus closer to the sun. In theory we could set up a system like this and just let it do its thing over a very long time, the change would be imperceptible over a human lifetime.
Add "running out of CO2" and "the atmosphere thins too much" to the list. I don't know when those could happen, but they've been happening slowly for billions of years, and they will finish happening eventually, most likely well before the Sun's output gets too high.
Atmospheric loss is an interesting and not-entirely-understood subject [1].
But here's one aspect we do know that puts the scale in context. Any gas has a Boltzmann distribution of kinetic energies. You can calculate that a certain portion of that will have a kinetic energy high enough to escape gravity. This is called the Jeans escape energy [2].
For Earth this amounts to losing 60-100,000 tons of atmosphere every year, which is actually a complete non-issue.
I mention this because the idea of terraforming Mars is a popular sci-fi trope but really makes absolutely zero sense. Mars has lower gravity (and no magnetic field, although part this is fixable) so the atmospheric loss would be significantly higher if we wanted to produce 1 atmosphere of pressure at the surface.
So however we produced that atmosphere would have to be able to sustain a loss of 100,000+ tons of atmosphere every year as a rounding error. That's the scale of just one of the many problems in terraforming Mars. You also have to produce (or ship in) that atmosphere without boiling the planet. The scale combined with thermodynamics makes this a nontrivial problem.
And where is all this energy coming from? We return back to the Dyson Swarm.
Jeans escape is not the only way an atmosphere can be lost.
If a planet doesn't have a magnetic field, the solar wind can directly erode the atmosphere (ionizing molecules and carrying away the ions and electrons in the magnetic fields of the wind.)
I got a lot out of your comment, but I don't know that Mars and Earth are directly comparable.
- Earth has nearly 10x the surface area of Mars. This decreases the rate of escape.
- Mars has lower gravity meaning escape velocity is roughly 1/3 Earth's, or escape energy is 1/10. This increases the rate of escape.
- Mars has lower temperatures, which reduces what fraction of the atmosphere is at an escape velocity. This reduces the rate of escape. Though if we terraform it, maybe it warms up as well?
So Mars and Earth are not easily compared, and are likely off by an order of magnitude.
Still, it is worth thinking about what general scale we are talking about. Terraforming requires a civilization with access to resources many times our own.
This [1] may interest you. It estimated Mars's atmospheric loss at 0.1-0.5kg/s, which amounts to about 3-16k tons/year but that's also with Mars's current almost nonexistent atmosphere. Losses would be higher with a thicker stmosphere that would be ~1 atmosphere of pressure at ground level.
Mars currently has less than 1% of Earth's sea level atmospheric pressure.
Cusco is roughly 0.6atm of pressure.
So Cusco is a lot closer to use. Mars is essentially the Moon. Actually, it's worse than the Moon. Because all Mars's atmosphere dos is blow really annoying dust all over your equipment. Everything about Mars is the worst [1] eg specifically about the problems of landing on Mars:
> “It’s like this annoyingly middle value,” he said. “The atmosphere is thick enough to cause you all the problems you have on Earth, but too thin to really stop you like on Earth.”
Right, but the idea is that if you had an atmosphere with a higher partial percentage of O2 you could get by with far less inert gas filler, which makes terraforming a bit less daunting. You could imagine an atmosphere with 35% O2 at 0.3 atm being possibly habitable and requiring many trillion less tons of material added to Mars.
Cody's Lab has a few interestig videos about burning things in pure oxygen. For example https://www.youtube.com/watch?v=JlSeHSDc-Do So it's no so simple becuae you can't just ignore the 80% of nitrogen and use only the 20% of oxygen.
(IIR/UC the problem is that the nitrogen absorbs heat, so the pure 20% of oxygens burn things too easily.)
I'm not arguing that Mars atmosphere is close to Cusco. I'm responding to the parent comment implying that 1 atmosphere off pressure would be lost very quickly on Mars. Would this be the same for 0.6 or 0.5 atmospheres? If we could create such an atmosphere is a whole different discussion
I believe that the issue is the loss rate exceeds the creation rate, making a viable atmosphere a nonstarter - not that "an atmosphere suddenly appears and lasts 100,000 years"
The "plans" for Mars terraforming will probably include slamming comets into it (at low relative speeds), on the scale of 1000-10000 years. It's unlikely to involve slow-and-steady air production.
I looked into this a while ago, and a major problem with Mars terraforming is that if you add a bit of additional carbon dioxide (or water vapor), it'll mostly just get frozen and deposited onto the ice caps.
So you need to add something like nitrogen to "bulk up" the atmosphere to prevent it from freezing out. And there's just no nitrogen on Mars.
I disagree. When one is only concernde about the order of magnitude, it should be given as 1*10^2 mya or as 0.1 bya. What the OP said is analogous to saying that one's grandfather died at the age of 100, when in reality he only lived to be 66.
Not all of those explode eventually, rather it's a small amount. Only the most massive stars explode into a supernova. The majority of stars are smaller, and will have different lifetimes. For example, the sun, an unusually bright star (brighter than about 95% of stars) will eventually turn into a red giant, slough off material then collapse to a white dwarf. It's estimated that the majority of stars are brown dwarf (very small, some not too-too much larger than Jupiter), and less than 1% of stars are massive enough to go supernova. The problem is that only the big stars go super nova, and the big stars also have the short lifetimes because they're burning fuel so quickly.
White dwarfs can also explode, if they are in a binary system. It's a different kind of explosion (more akin to a thermonuclear bomb) but it also produces iron.
They did? I need only step into my back yard to see birds and lizards.
> remarkably common event
Probably not normally distributed but depends on the age of a given galaxy. But indeed, it does look like they are not super uncommon in our neighborhood.
The correct term is "non-avian dinosaur" for the ones that died en masse, but making that point in the first place is already pretty pedantic, doing it with snark is just being annoying for the sake of being annoying.
We're far off the topic of the thread which is iron-60 supernova paleoarchaeology but I can't help myself from pulling things even further off-course. Did you know there were flying dinosaurs in the medieval era that hunted humans from the skies?
- "'[Haast's] eagle had the possibility to hunt people,' Joanne says. 'It's hard to imagine a bird in that role but if it could successfully hunt a 250kg moa, then 80kg humans were possibly on the menu. There is oral tradition which suggests it was the case.'"
Oh they'll come back together, sooner or later, because of gravity. They'll form a gas cloud at first, which condenses into a new star and its planetary system.
We're all made from star dust, and will become star dust again.
They're actually much closer to equal, if you account for the duration of the supernova light curve.
It's a somewhat relevant difference. A supernova 4 light years away, with all the energy released instantaneously like a bomb, should ignite and vaporize everything on one-half of the planet. That's a wrong calculation. The peak rate— the peak luminosity of a type Ia supernova, for example (10^43 erg/s or 10^36 W—a famous standard candle) would be no more than 50 W/m^2, from the distance of Alpha Centauri. That's about a 5% addition to the solar irradiance, sustained over a few weeks—probably just a moderate change in weather patterns.
Right; I elided from one to the other to give a calculation of interest to the thread topic. (I had thought I had written it sufficiently clearly? What should I change?) The "sol" case is still at the hydrogen-bomb level—but not 9 orders of magnitude beyond it.
Because there's few reference points with which to interpret numbers on the scale of 10^12 Watts/meter^2, and it doesn't fundamentally change the XKCD outcome anyway (from the human perspective). I thought shifting it to nearby stars made it topical to this thread, where multiple comments are asking about the impact of galactic supernovae.
(That's the less important part of my comment, and I'm not sure why people latched onto it! The important part is that supernovae are >7 orders of magnitude slower than hydrogen bomb explosions).
Well for starters you did not say that supernovae are >7 orders of magnitude slower than hydrogen bomb explosions, and it sounds an awful lot like you misinterpreted the original statement as referring to a supernova 4 lightyears away, which would coincidentally lower the value by about 9 orders of magnitude.
No, the article says the only noticeable effect was a particularly bright star. The same amount of material received from the supernova is absorbed by earth each day. It was an ordinary Tuesday besides the lightshow.
An exceptionally large cosmic radiation source could cause mass extinctions—it's a postulated explanation for several of the geologic ones. That's not due to the radiation itself. The mass column of the atmosphere—equivalent of a 10-meter thick water layer—is plenty adequate radiation shielding. Rather it's secondary effects of the interaction of radiation with the high atmosphere, such as the destruction of ozone.
"As matter expands away from the blast site, it thins out, so by the time the ejecta from a nearby supernova reaches Earth, perhaps a few hundred metric tons might rain upon our planet over a length of time. That might sound like a lot, but about that same amount of meteoric material slams into our atmosphere every day. So supernovas aren’t appreciably adding to Earth’s weight, nor are they a big danger to us in this way."
Is there a way to filter out articles that are pay-walled? I know this is unrelated to the article but I’m curious as I’m tired of clicking on links and being unable to read them.
Expanding on the sibling's link you can prepend "archive.is/" to the url and it'll either have a snapshot already or you can click the link to create one. Typically a popular article that paywalls itself will have one of these links in the comments already as well.
I think it's one of the more annoying policies on the site (won't avoid paywalled posts but also hides that it expects everyone to do that workaround to participate anyways) but it's pretty easy to deal with once you know the above dance.
Scientists have found evidence of two separate supernova events in the last 7.5 million years that showered the Earth with radioactive debris like iron-60. These events were traced back to the Scorpius-Centaurus association of young, massive stars about 300-400 light-years away.
While the amount of supernova material that reaches Earth is tiny compared to the total ejecta, it indicates that our planet has been bombarded by radioactive ashes from exploding stars thousands of times over its history.
The most recent known nearby supernova event may have been visible in the sky to early human ancestors like Australopithecus afarensis, appearing as a bright star or "guest star" in the sky
While that's an interesting argument I don't this applies to the Fe-60 isotope. I don't think we know of an energy production process (fission or fusion) that would result in Fe-60 as a byproduct which would cater to the Silurian hypothesis.
Especially in the quantities and locations discovered. Hence I think their assumptions - of looking for natural places where the isotope is forged - in this case are valid.
A DT fusion reactor with iron in its structure would produce a small amount of Fe-60, by double neutron capture on Fe-58. The amount would be limited because the half life of Fe-59 is 44.5 days.
Because it seems pretty ridiculous on it's face. We might not have monuments of an ancient civilization, but we'd expect to see records of an equivalent anthropocene in the geologic record, similar to what we're making now, more or less. Increased bio-carbon deposits, increased sedimentation from agriculture, etc.
We might as well wonder why scientists didn't consider whether the deposits of iron 60 were put there by mischievous leprechauns.
'scientists' need not consider every crackpot theory because someone on the Internet thinks they should.
It's ridiculous because a past civilization wouldn't have spread iron-60 all over the planet the way a supernova would have.
But a fairly advanced civilization could have existed in a fairly local part of the planet that we don't much explore (think of the Sahara desert) and so haven't found the remains of, or it could be buried or under quite a bit of water (if it developed during a glacial period).
It’s not so ridiculous once you learn that most of the earths crust gets recycled within 500 million years, and more than half gets recycled within a mere 100 million years.
That’s why we don’t find fossils everywhere. And if humanity goes extinct today, it would be fairly tricky to find evidence of us in a billion years.
It’s of course a non falsifiable hypothesis, so there’s not much we can do. But plenty of people believe in another non falsifiable hypothesis——invisible man in the sky.
This isn't really accurate. There are some plates that are extremely geologically stable, location-wise. There are parts of the Canadian shield over 4 billion years old.
That is completely false. Most of Earth's continental crust is more than 2.5 billion years old, with the oldest parts being 4 billion years old. Only Earth's oceanic crust is young.
We do find fossils everywhere. Not all rock types are conducive to fossil formation, and many parts of Earth are less explored than others, but there exists no region on earth without a fossil record.
Evidence of humanity's existence would be clear in the fossil record for billions of years. Reinforced concrete, plastics, artificial ceramics, mined fertilizers, they would all be preserved over geologic timescales. On top of this, intelligence does not simply pop into existence - there would need to be many millions of years of fossil record showing the evolution of some intelligent lineage.
> On top of this, intelligence does not simply pop into existence - there would need to be many millions of years of fossil record showing the evolution of some intelligent lineage.
What is the evolutionary gradient leading to “intelligence?” Where is there evidence of .99, .98, .97.. of Human intelligence?
Could an intelligent life form not leave a fossil or any other record? Is a material culture always evident where human-level intelligence exists?
If this civilisation was advanced enough to forge fancy isotopes they were probably advanced enough for space travel. They would have visited the Moon and Mars but there's no evidence of that, which is especially suspicious on the Moon as it's geologically inactive.
It would be really weird if a Silurian civilization randomly pumped out a bunch of radioactive iron and didn't do anything else.
Any industrial civilization comparable to ours within the past few hundred million years would be very detectable today - reinforced concrete, plastics, ceramic shards, mined fertilizers, all would show up in the geologic record. Further one would expect fossil evidence of some lineage approaching intelligent levels over time. The only plausible place for a Silurian civilization to hide would be several billion years ago, so long ago that the crust they lived on has been subducted back into the mantle, taking the evidence for their existence along with it.
I agree with this comment fully but I just wanted add a little on the subduction.
It’s a lot quicker than people think.
The vast majority of rocks we can find that aren’t of extra terrestrial origin are only around 200 million years old.
>A few seams of very old rock have been discovered, such as the billions of years old Nuvvuagittuq greenstone belt in Hudson Bay, Canada, as well as similarly ancient outcrops in Australia, China, Greenland and South Africa. But even this very old rock has had a complex history. “Exposure to high temperatures during past collision can change the chemistry,” notes Boyet. “This disturbs the isotopic system we use for dating rock.”
Most continental crust is over 2.5 billion years old. Very old rocks aren't exposed at the surface very frequently, because they tend to get covered over in younger rock, but it's still there, and we can sample it with deep drilling.
Oceanic crust tends to be less than 200 million years old, though even then there are some much older examples.
> It would be really weird if a Silurian civilization randomly pumped out a bunch of radioactive iron and didn't do anything else.
We never know any data before interpreting it through theories. All observations are, as Popper put it, theory-laden, and hence fallible, as all our theories are.
Deutsch, David. The Beginning of Infinity
Probably the best evidence that Fe60 is not "Silurian" in origin is that it still arrives on Earth [0].
The Silurian Theory is sometimes an interesting way to explore ideas. I don't think that a large pre-human "civilization" need take the same form as what we think of as human civilization. Even some large human civilizations like that of the Indus River Valley or Harappan culture are less understood because they left less in the way of stuff analogous to current times: "In sharp contrast to this civilisation's contemporaries, Mesopotamia and ancient Egypt, no large monumental structures were built. There is no conclusive evidence of palaces or temples."
- Nearby supernovae
- Gamma ray bursts (eg from a neutron star that happens to be pointing directly at us and is sufficiently close)
- Large icy or rocky bodies hitting the planet
- Coronal mass ejections
- In about 1.6 billion years the increasing Solar output will make Earth uninhabitable
- In about 4 billion years the dying Sun will expand and essentially swallow the Earth, which will be long dead anyway
And here's a list of terretstial civilization killers:
- Supervolcanoes
- Climate change
- Global war
- Disease
- Ice ages
There are also others that we don't know how disruptive they will be other than probably super disruptive like the magnetic poles flipping (yes, this has happened at least 30 times).
My point here is that living on Earth is living on borrowed time. To survive in the really long term, we are going to have do something pretty drastic. Whatever we do (eg interstellar travel, moving the EArth--yes, this is possible) will require such massive energy expenditure that IMHO the only path forward will be to build a Dyson Swarm.
I'm also not yet convinced we can think of the time scales required to avoid our own destruction but at least, for a brief period of time, we will have created an awful lot of shareholder value. Over sufficiently long time periods, all of these turn from an "if" into a "when".