Evidence for nuclear explosions on Mars [pdf]
hou.usra.edu
hou.usra.edu
EVIDENCE FOR A LARGE, NATURAL, PALEO-NUCLEAR REACTOR ON MARS. J. E. Brandenburg
http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1097.pdf
However, over time he has been getting deeper and deeper into pseudoscience. It was covered in Pharyngula a while back:
http://scienceblogs.com/pharyngula/2014/11/22/the-two-faces-...
I can't stand this secular inquisition bullshit of cherry picking any sign of possible 'out there'-ness and using it to completely trash peoples' entire bodies of thought and work. It's anti-scientific. Please point out a problem with Brandenburg's actual published work, or go away. Even if he does hold non-traditional or strange religious beliefs, it's not relevant. Roman Catholicism is no more rational than Eastern mystic cults, so do we throw out all scientific papers by Roman Catholics?
I'm not much of a fan of PZ Myers either. I read him a bit back during the mid-2000s 'intelligent design' creationist PR offensive, but stopped reading him as he got more and more shrill and irritating. IMHO Myers is as much a shrill fundamentalist as the religious bozos he constantly wars with.
One interesting thing Brandenburg did say was that when he came to believe himself that Mars had been nuked, possibly in act of "biosphere genocide," the realization that this might have actually happened plunged him into a bit of a metaphysical crisis. He immediately thought of the Fermi Paradox, and that maybe the reason we're not hearing/seeing anything is because there are big nasty genocidal intelligences out there that 'cull' anything interesting from the universe. He said he actually got very depressed, and got deeper into religious/mystical stuff as part of this.
That doesn't sound crazy to me, just human. Around here we've seen some IMHO irrational fears of super-human dangerous AIs circulating recently, and it seems to have led to a similar amount of metaphysical anxiety among some very brilliant and notable people in the CS field.
I'm very skeptical of Brandenburg's thesis here, but I have to admit that the evidence he puts forward is very interesting. It either points to what he says -- some kind of incredibly ancient use of a nuclear device -- or an as yet undiscovered natural phenomenon that can yield a similar signature.
One possibility (other than 'reaper' aliens) I can think of would be a natural nuclear reactor that actually went fully supercritical and detonated. Another would be a hypervelocity object, possibly traveling at some significant fraction of the speed of light, that impacted Mars and went thermonuclear in the atmosphere on kinetic energy alone. Maybe an asteroid or comet that got flung by a high-gravity body (black hole? neutron star?) or supernova debris could do that?
> That doesn't sound crazy to me, just human."
I linked to a reasonable article by him to establish that he wasn't just a nut, but we'll have to agree to disagree on his metaphysical crisis, because the speculation that anomalous levels of radiation in parts of Mars is due to "big nasty genocidal intelligences," that sounds Dianetics-level bonkers to me.
I think he's drawn attention to some very interesting data, but that's where I get off the bus.
Update: I actually watched the video he did with Supreme Master TV, give it a look and judge it for yourself: http://youtu.be/NBuN3uHnjYY
Like so much else, "it depends". If you're sure that's the explanation and no other makes sense, you're bonkers... our knowledge isn't strong enough to make that claim exclusively.
However, as answers to the Fermi Paradox go, "Something out there stomps flat anything that looks like a developing civilization", as unpleasant as it may be to contemplate, is definitely in the running. Along with a difficult-to-bound number of other candidate answers, but it's not a crazy one based on the meager evidence we've collected to date on the topic.
* That life in our galaxy is unique to our planet given our now solid knowledge that similar planet systems and planets of the correct size in habitable zones are beyond abundant
* That intelligent life, given the above, is also not unique to our planet
* That some intelligent life is not millions of years more advanced
* That there is nothing capable or motivated to wipe out entire planets for reasons to us which seem irrational and murderous
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Lots of folks get confused between the increasing rationality of assuming life exists somewhere besides Earth and conspiracy nuts who think every unusual weather phenomenon and experimental aircraft is an alien.
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The disconnect and irrationality comes from attributing non-Human sentience to unexplained phenomena.
If your foot hurts, it's pretty easy to go on WebMD and convince yourself that you have bone cancer. It's not irrational because it's impossible, but because your overactive imagination has chosen the most interesting solution over the most reasonable one.
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Likewise your mind shouldn't be closed to the idea of something we observe in the next century being definitely attributable to extraterrestrial intelligence; but it will take some extraordinary exclusion of natural happenings to make it conclusive.
The latter belief is supported by a lot of evidence: the molecular machinery of our kind of life is pretty common, and the chemistry that drives it appears to be robust and nothing special.
To get a sense of how special the kind of intelligence that builds spaceships is, however, consider that every complex feature of organisms, from insect societies to wings to eyes, has evolved many, many times, all independently of one another.
Intelligence of the kind that builds spaceships, on the other hand, has evolved exactly once in the history of our planet, and appears to have been the result of a runaway mate competition and mate selection process in our social primate ancestors. There was certainly no material advantage to having a brain big enough and well enough designed to build spaceships when you were busy scrabbling for food (a feat that a huge range of unintelligent organisms, including unintelligent social organisms, manage reasonably well.)
So it is quite plausible that there is life all over the place in the universe, and intelligence almost nowhere. Just because we can see the advantages of intelligence doesn't mean there is a clear evolutionary path toward it, and the history of life on Earth suggests in fact that the path to the kind of intelligence that builds spaceships is extremely narrow and twisty.
Life as such might be common as mold in cosmos but utterly unable to move from star to star or even broadly choose it's "destiny".
- And simplest hypothesis is that if these Martians existed, they wiped themselves out, as it human beings seem on the way to doing. What are the odds?
While an appealing argument, it is in actuality sophomoric, not the sophisticated argument it fancies itself. Independent probabilities stack exponentially; as we look out into our universe, chances for life only expand somewhere between n^2 and n^3 as we look farther out (it's not pure n^3, our universe has vast empty spaces). We don't know what is really required for life. It could be little more than "a space to grow and some sunlight", but then, we kinda know there's a bit more to it than that from our own Moon. It could also be a surprisingly large stack of requirements (see any ol' Rare Earth argument, as all I'm referring to is the possibility that it could be a large stack), in which case the mere presence of bajillions and bajillions of planets are irrelevant in the face of what could be 1:2^bajillions odds.
We do not know. "But there's so many planets out there!" is just your human mind being blown by large numbers, not a scientific argument. We can not establish that the odds against life may well be even larger numbers. And we can establish through arguments such as the Great Filter [1] that if life is in fact abundant and easy, there's still something very wrong with our understanding of the universe. If it's so easy to be alive and intelligent, we really, really ought to see a different universe. "There's so many planets, how can life be rare?", as emotionally appealing as it may be, hasn't got a very good answer for that. It isn't the last word on the topic as you are presenting it.
It was not about ruling anything out, or a statement that any particular position was irrational.
As you can see in my other posts, in general I'm mostly arguing against certainty of any of the options. I've got my personal guesses, which I am not ashamed about, we are all entitled to our guesses, but intellectually honest people must put error bars on them that fill pretty much the whole probability range. But, by the same token, we can't eliminate very many of them either.
If one believes the radiation anomalies are from nuclear explosions, it seems at least remotely plausible that they came from off-planet (because who would do that to their own?). At that pointpoint it's not entirely lunacy to consider the existence of genocidal aliens.
None of that means that any of those are true, but each seems to be an explanation that might occur to any normal person who accepts the preceding points. The idea of genocidal aliens has been part of our cultural zeitgeist for some time -- isn't that the premise of Mass Effect?
Occam's Razor dictates that the simplest answer is probably correct. What's simpler:
A) This is the result of a naturally occurring process that has happened on our own planet.
B) Aliens
The more recent paper seems like a rehashed subplot from Heinlein's "Rocket Ship Galileo"
From chapter 11:
Morrie grasped his arm, to steady himself apparently, but quite as much for the comfort of solid human companionship. "You know what I think, Ross," he began, as he stared out at the endless miles of craters. "I think I know how it got that way. Those aren't volcanic craters, that's certain—and it wasn't done by meteors. They did it themselves!"
"Huh? Who?"
"The moon people. They did it. They wrecked themselves. They ruined themselves. They had one atomic war too many."
"Huh? What the-" Ross stared, then looked back at the surface as if to read the grim mystery there. Art stopped taking pictures.
"How about it, Doc?"
Cargraves wrinkled his brow. "Could be," he admitted. "None of the other theories for natural causes hold water for one reason or another. It would account for the relatively smooth parts we call ‘seas.' They really were seas; that's why they weren't hit very hard."
"And that's why they aren't seas any more," Morrie went on. "They blew their atmosphere off and the seas boiled away at Tycho. That's where they set off the biggest ammunition dump on the planet. It cracked the whole planet. I'll bet somebody worked out a counter-weapon that worked too well. It set off every atom bomb on the moon all at once and it ruined them! I'm sure of it."
I'm not arguing against Occam's Razor. I actually think, given those broad questions, that we haven't even begun to scratch the surface of the simplest explanation(A).
Once one begins hypothesizing "things that can do anything in ways we don't understand for reasons we don't understand but occasionally do some things we do understand but again for no clear or unambiguous reason" then one's ability to use Occam's razor is gone.
Maybe a spaceship go marooned on Mars and exploded in the process of trying to fix it's warp drive. What are the odds? Clearly we don't know what the odds for any of this.
A simpler hypothesis is a supposed Martian civilization wiped out itself. No necessarily true or supported by much evidence but it seems at least sort-of testable since it doesn't assume variables beyond our conception of what's possible. Human civilization has been poised on the brink of large-scale nuclear in the not-too-distant past so intelligence creating world-destroying-nukes hardly seems like that big a stretch.
We don't know of a way to travel between them _quickly enough to be practical for humans_. That's not a problem for machines. They can be patient and take thousands of years.
Well, as far as we know, 100% of all species who can do it, will do it.
Maybe that's why the entire galactic community didn't want to believe in the existence of Reapers - "Genocidal aliens cleaning up the entire galaxy? Now this is just bonkers!".
He could've consulted with another subject matter expert, but instead he decided to act as though the very notion of an ancient civilization on Mars getting nuked to extinction is prima facie absurd, and then ended his article with the kind of things you'd expect to hear from a Fox News anchor.
And I say this as someone that thinks the chances of any advanced civilization having been on Mars at any point in the past, let alone getting nuked to death, is ... rather unlikely.
PZ Myers is probably right, but in this case, it's only accidentally.
"This article was written in early 2005, and submitted then to Science. Perhaps predictably enough, it was rejected."
Reminder: http://scienceblogs.com/principles/2012/01/30/the-arxiv-is-n...
The link you provided is interesting speculation, perhaps an amusing philosophical exercise, but if you think it's science, then we aren't talking the same language.
That's not some irrelevant religious belief. That's a chunk of unscientific nonsense at the very core of his claims. Pointing out that it is in fact nonsense is not somehow "cherry picking."
Zoom in all the way, scroll up and to the right as far as possible, then scroll down just a tiny bit and look at the rock. That rock has a face on it? Definitely a WTF from me.
I am so tired of seeing visual evidence dismissed by people who refuse to even consider it if it's not endorsed by some large "respectable" institution. You mean to say this rock is just a naturally occuring anomaly? Really?
Upon further investigations they found large numbers of them throughout northern Africa, they described all kinds of megalithic structures: dolmens, menhirs, cairns, cup stones, and sacrificial altars.
Speculation was that this was a previously undiscovered Neolithic civilization, in describing the Senams, Cowper wrote "there had been originally no less than eighteen or twenty megalithic trilithons, in a line, each with its massive altar placed before it." Amazingly each altar had an obvious drain trench where blood from the sacrifices flowed. Cowper even speculated at one point that the builders of these cyclopean structures were involved in the raising of Stonehenge.
They were all well-respected, H.S. Cowper had done some early significant work identifying and describing megalithic structures in the UK, so obviously he knew what he was talking about.
A book with the findings was published to great anticipation. Unfortunately as the book was going to press, an article was written by J. L. Myers, Arthur Evans, and W. Gowland who actually knew what those structures were.
They were Roman-era oil presses.
For a brief period of time, Cowper denied this was possible pointing to Berbers that referred to the structures as idols, but for anyone who knew anything about Roman oil presses, these were fairly commonplace.
That's the long way of saying that the human mind has a tendency to find patterns and to try to explain those patterns based on their expectations.
But sometimes a cyclopean altar is just an oil press.
http://en.wikipedia.org/wiki/Pareidolia
Yes, that rock is almost certainly just a naturally occurring anomaly. People are built to find faces, even in things that aren't actually faces.
We've known for a long time that we are hardwired to recognize faces in sets of items that are definitely not faces, so why is it so hard to believe that you're falling prey to the same thing?
- Install Gimp
- Download the original Nasa image linked here: http://mars.jpl.nasa.gov/msl-raw-images/msss/00184/mcam/0184...
- Open the picture with Gimp. Crop out the face. Under the image tab, choose scale image. Scale the image to 300 percent of original size. There is an interpolation option when scaling the image. You have to choose Sinc Lancoz 3 because that is the interpolation option that will preserve the data in the jpeg pixels. If you choose cubic or linear it will be lost.
- Under the colors tab, open curves. NASA obscured this image by destroying it's dynamic content, so you will need to expand what is there by pulling the line to perfectly match the top and bottom of the image data. This will render the jpeg blocks and show you the image data they contain.
- Under the filters tab, mouse over enhance and choose the last option "Unsharp mask". Apply unsharp mask twice with the default settings. The picture will become clear enough to show.
Also, suppose he did come back with a rawer image that still showed the features. Is that going to convince you to say "oh wow maybe it was carved, it couldn't have naturally occurred!"? (http://lesswrong.com/lw/wj/is_that_your_true_rejection/)
For anyone not versed in this stuff, JPEG works by breaking the image up into 8x8 squares (possibly 16x16, or 8x16, or 16x8, but 8x8 is standard). For each square, the encoder then transforms the pixel data into the frequency domain using the discrete cosine transform. The frequency data is then what is ultimately losslessly compressed and encoded in the actual JPEG data.
Now, here's a zoomed-in screenshot of the rock in question, taken from the original JPEG with no alterations whatsoever:
http://mikeash.com/tmp/screenshot_F574A0FB-5919-4E2C-AEA3-C3...
The 8x8 grid stands out like a sore thumb at this zoom level. You can clearly see that the vertical separation of the "teeth" are just macroblock boundaries. There is clearly an actual horizontal dark streak in there, but the division of the areas above and below into separate vertical "teeth" is, to me, blindingly obviously a JPEG encoding artifact and nothing more.
Would I be convinced if the raw images showed these features as well? Probably not. But that doesn't invalidate my point. If somebody showed a picture of Bigfoot, and I noticed that their supposed Bigfoot is wearing a digital watch, it would be perfectly reasonable to point that out. Explaining away the watch would not silence my doubts, but it's still a completely reasonable thing to point out when someone shows a picture of Bigfoot and he's wearing a digital watch.
Do I know how to obtain a raw image? Nope. I wish I did. I briefly searched around for one, but with no success. My point is simply that JPEG images cannot be relied upon for fine detail, and if one is going to make claims about Mars rovers finding alien statues, the evidence needs to be clearly not due to JPEG artifacts, preferably by finding the original, uncompressed data. Scientists don't use JPEG-compressed photos for analysis, and this is why. The fact that a raw image is difficult to obtain is unfortunate, but completely not my fault, and doesn't alter the facts that 1) you really need a raw image to say anything about this photo and 2) the "teeth" in this photo are really, really, really clearly JPEG macroblocks.
If you really want to go deep into this, try some of the other cameras around that time, maybe you'll see it from a different perspective.
1: http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=184&camera=MA...
2: http://mars.jpl.nasa.gov/msl-raw-images/msss/00184/mcam/0184...
We know that humans and many other animals recognize faces in a heavily biased way. It's the evolutionary reason why some butterflies and fish have eye markings. Their potential predators tend to see faces and may be intimidated by the implied size of the creature with those eyes or mistake the direction that the prey is headed.
Just from our own subjective experiences, we all see faces where we shouldn't: In clouds, in rock formations, in foliage, and even in burnt grilled cheese sandwiches:
http://www.nbcnews.com/id/6511148/ns/us_news-weird_news/t/vi...
As human beings who want to do Science, we have to recognize the limitations and biases of our own hardware or we're doomed to fail at evaluating reality.
http://en.wikipedia.org/wiki/Cydonia_(region_of_Mars)#.22Fac...
Of course it is. That's by far the most likely conclusion.
Consider: Curiosity alone sends back between ten and 100 images every day that each contain thousands of objects (mostly rocks). So let's say there are 10,000 objects a day that people can look at (many more if you consider the tiny size of the "face" in this compressed image.)
I can't find any actual data on apophenia and pareidolia (finding patterns and faces in randomness, respectively) but given what we know about it the incidence is unlikely to be less than 0.1%, which means we'd expect to see ten objects per day in Curiosity images that look something like a face or other recognizable object, so if a fraction of one percent of those instances are fairly realistic we would expect to see something "very face like" a few times a year.
Those numbers are a bit hand-wavy, but they aren't out by orders of magnitude, and from them we can conclude that it would be pretty surprising if we didn't see something pretty facelike now and then in Curiosity imaging. If we didn't, it would be a major surprise. That we do... well, it's what we expect, so we dismiss it as evidence that what we see is of artificial origin. To do anything else would be to ignore what we know about human perception.
That image looks like a rock and zooming in makes it look like a distorted rock. Coloring and manipulating the image is in my opinion getting farther from convincing there's something uncanny about that rock.
I saw a really good one the other day when I was looking unfocused at the floor and caught two patches of ground with either eye that resolved themselves really nicely into a stereoscopic image of a cartoon dog.
In hypothesizing possible causes, I wonder about the relative size of the ejecta of a type 2 super nova. Given that the Uranium, on the planet originated in such events at some point, and the 4.7 billion year half life, one could imagine perhaps a modestly dense fragment cloud of U235 which was traveling at relativistic velocity away from a Type II supernova, and it collides with the atmosphere of a planet in a far away star system. If the pieces were small enough they might simply heat up and impact the ground, however if they were massive enough, the shockwave of hitting the atmosphere might be sufficent to compress them into a supercritical mass. At which point the meteor would undergo rapid, and energetic, disassembly.
Or did I miss something? :)
So imagine you've got a bunch of sub critical chunks all in a line, they hit an atmosphere which gets them to pile up like a line of tailgating cars on the freeway. The numbers should be quite computable to figure out a bounds box on the possible yield.
[1] http://en.wikipedia.org/wiki/Thin_Man_%28nuclear_bomb%29
http://journalofcosmology.com/JOC24/Brandenburg.pdf
Pages 20 to 46 are about the "faces on Mars."
The "happy" one is interestingly not mentioned:
Still I fully understand that he got really worried, previously actively analyzing the effects of the nuclear tests on Earth and seeing the same stuff on Mars.
In fact, we all should be more worried than we are about the really not improbable destruction on Earth.
However, Brandenburg doesn't do himself any favours by saying things like "The Natural Nuclear Reactor Hypothesis had the merit that it provided a known source for a large nuclear explosion."
Natural reactors, so far as we know, have to be slow-neutron moderated, and slow-neutron reactors are not sources of nuclear explosions. Even fast reactors--which if not actually impossible are certainly much rarer in nature than slow neutron reactors--aren't sources of nuclear explosions unless things go wrong in ways that no one has yet been able to imagine. I won't say it's impossible, but it is wildly, wildly improbable.
Granted the distribution of radioactive elements on the Martian surface is anomalous (which I'm only aware of through this article, so I'm going to take with a grain of salt) the hypothesis that leaps to mind is a natural slow-neutron reactor that was close to a perfectly ordinary large meteor strike.
We know that Mars was wet in the past (a requirement for natural reactors) and we know that the early solar system was richer in fissile isotopes, and we know that there was at least one natural reactor two billion years ago on Earth, and we know that meteoric impacts were common in the early solar system and that Mars got hit hard and often enough for us to be able to identify a whole class of meteorites that come from Mars.
So a natural reactor that got hit by a large impact doesn't require anything wildly improbable, and is likely testable via detailed analysis of any impact structures and glass droplets from around the areas with high concentrations of uranium and thorium.
> Maybe an asteroid or comet that got flung by a high-gravity body (black hole? neutron star?) or supernova debris could do that?
I don't think a black hole can fling any particle with speed orders of magnitude higher than the initial speed of either the black hole or the particle.
Reminds me a lot of Roko's Basilisk (http://rationalwiki.org/wiki/Roko%27s_basilisk) and the breakdowns that ensued amongst the LessWrong community.
Correct me if I'm wrong, but I always thought it was because Mars' core cooled, which caused its magnetic field to go away, resulting in all its water floating off into space. No water = sterile planet. You could shoot every nuclear weapon in the world at the Earth and life would still easily carry on (maybe not multicellular, but life nonetheless), but take all the water away...
The author then argues that the evidence seems to fit an atmospheric explosion better, for example an asteroid that exploded in mid-air like in Tunguska. Or that the radioactive stuff just got there in this pattern through geological activities and other processes.
Did I miss the part where he talks about nuclear weapons or sterilization?
Yes, it's in a different link where he 'furthers' his work.
(courtesy of the Supreme Master Ching Hai International Association cult)
The world could fire off every one of its functioning nukes simultaneously, and it would not come even remotely close to ending multicellular life. Most of the planet would not even notice the event; it could destroy, including the damage from fallout, an area smaller than the United States. Humans of course would likely become an endangered species were the blasts spread out targeting population centers.
Bayes' rule tells us the plausibility [$] of a proposition after taking into account some evidence should be the prior plausibility times the probability of the evidence occurring if the proposition is true divided by the probability of the evidence regardless of whether or not the evidence is true, so vastly improbable occurrences that would be way more probable if the proposition was true count as very good evidence, but lots of things can shift our degree of belief a tiny little bit.
However, you are correct that the prior has such a minuscule prior plausibility that it'd take astonishing evidence that couldn't be explained otherwise to raise the posterior plausibility up to "worth taking very seriously" level.
Beyond that, there is the practical consideration that we impose a threshold on our beliefs for purely pragmatic reasons. Below some plausibility it just isn't worth our time to even consider the issue. So in that sense, you are Bayesianing with the best of them.
[$] I am a heterodox subjective Bayesian, in that I maintain a strict separation between "plausibility" and "probability". Plausibilities are degrees of belief by a knowing subject in a proposition, and as such are inherently subjective. Probabilities are measures of the likelihood of events, and by far the most common measure is the frequency. I take orthodox Bayesiansism to be in error by identifying plausibilities with probabilities, which is what creates the great subjective/objective quango. Bayes' rule on my view is Pl(H|E) = Pl(H)*Pr(E|H)/Pr(E) where Pr = probability and Pl = plausibility.
We are the aliens!
explosion
[0] http://www.wolframalpha.com/input/?i=mass+of+the+asteroid+be...
Whether we have the data to parse out something to this level of detail on Mars when we're still arguing about what killed the dinosaurs on this planet I'm substantially more "meh" about. But it is not, intrinsically, impossible or stupid.
The same goes for the alien hypothesis... but even taking the possibility seriously, I'd submit that A: we don't have enough evidence to eliminate the possibility that Mars could have once had an intelligent civilization but B: even moreso, let me underline that, even moreso, we have no evidence to suggest that it ever did. Such speculations would be pure science fiction right now. Right now we still know very little, full stop.
And I'd observe that the stories about these civilizations, viewed through modern technological eyes have some really weird aspects to them, such as, why would a civilization with technology capable of destroying planets (and, in this case, really, really destroying them, Death Star-style, not merely sterilizing the planet which is literally ten+ orders of magnitude easier [1]) only settle on Earth after the disaster? We're not planning on waiting for Earth to go bad before heading to Mars... we're pretty much only blocked on the requisite tech and on cosmological scales the instant we have it we'll be there. There's little reason to believe that a technological civilization of that scale would actually be destroyed even by its home planet going up in smoke. I'd submit the most likely hypothesis is that they were indeed written by humans thousands of years ago, who ultimately had no idea what technology was going to look like. (Heck, even we futurists are still only grasping at smoke in terms of what we'll have 50-100 years from today, to say nothing of trying to guess thousands of years ago....)
Why have they not bothered to come get us yet? We have our own nukes. They waited a little too long, or so it would seem.
Now, if they wiped out Mars with a designer black hole, or something of that nature, I'd say that we're still not too big for our britches for them to come do the same... but if they're just lobbing atom bombs, then they're overdue.
It's almost certainly some sort of natural, random event. If not another Oklo, then something not so different from it.
Oh, any alien genocider that may or may not exist would still be thoroughly unimpressed by our ability to fight back. Anything that could cross the stars in any period of time since civilization started need simply ram Earth to wipe humanity out as we know it. Call it a 10000 kilogram craft travelling at one-thousandth the speed of light from Alpha Centauri, setting sail 4000 years ago or so; if that simply rammed Earth it would be ~150,000 Hiroshima bombs [1]. That's pretty conservative for a genocider's capabilities, really, too. Obviously they're not right here, so anything that can travel here in time to get us is also a weapon that can wipe us out.
(This is to say nothing of the extreme opposite end of the scale and what a mature nanotechnology ought to be able to, even without Drexlerian extremes. I sometimes ponder "Our entire civilization was uploaded in its sleep ~3000BC and the real Solar System has long since been converted to computronium, and the simulated universe is lifeless to keep the processing simple." Pick your date of upload to suit your taste.)
To be clear, while I remain open-minded my current "top-probability" pick for resolution to the Fermi Paradox is "life is far more rare than science currently guesses". But it's still fun to discuss the alternatives and it's not like I could put that even remotely near 100%... it's just my best guess in a field where we have virtually no data, and YMWV.
[1]: https://www.google.com/search?q=10000kg++*+%2830000km%2Fs%29... - 63TJ is the Hiroshima explosion size.
It would be far more likely that they would be at least as sophisticated as humans, with emotional and strategic reasons, complex governments that change every now and then etc. By now they would probably be entirely different people from back then, just as our ethics evolve and and human empires rise and fall over a few centuries.
I don't think it's a very likely theory, but I don't see a general problem with it.
[This is all based off the nonsense Planet X theories that were going around. There was a good serialized YA novel that mined the ideas for plot, along with other Ancient Aliens nonsense, to quite good effect)
P.S. Not that I support the OP's line either.
http://www.ncbi.nlm.nih.gov/pubmed/20463738
> Among a wide range of biological models involving the independent ancestry of major taxonomic groups, the model selection tests are found to overwhelmingly support UCA irrespective of the presence of horizontal gene transfer and symbiotic fusion events. These results provide powerful statistical evidence corroborating the monophyly of all known life.