Arizona Scientist: We Could All Be Martians


As long as we’re still pondering human origins, we may as well entertain the idea that our ancestor microbes came from Mars.

And Jay Melosh, a planetary scientist from the University of Arizona in Tucson, is ready with a geologically plausible explanation.


“Biological exchange between the planets of our solar system seem not only possible, but inevitable,” because of meteorite exchanges between the planets, Melosh said. “Life could have originated on the planet Mars and then traveled to Earth.”

Jay Melosh. Credit: Maria Schuchardt, University of Arizona Lunar and Planetary Lab

Melosh is a long-time researcher who says he’s studied “geological violence in all its forms.” He helped forge the giant impact theory of the moon’s formation, and helped advance the theory that an impact led to the extinction of the dinosaurs 65 million years ago.

He points out that Martian meteorites have been routinely pummeling Earth for billions of years, which would have opened the door for past Mars microbes to hitch a ride. Less regularly, Earth has undergone impacts that sent terrestrial materials flying, and some of those could have carried microbes toward the Red Planet.

“The mechanism by which large impacts on Mars can launch boulder-sized surface rocks into space is now clear,” he said. He explained that a shock wave spreads away from an impact site faster than the speed of sound, interacting with the planetary surface in a way that allows material to be cast off – at relatively low pressure, but high speed.

“Lightly damaged material at very high speeds,” he said, “is the kind of environment where microorganisms can survive.”

Scientists have recent evidence of Earth microbes surviving a few years in space. When the Apollo 12 astronauts landed on the moon, they retrieved a camera from Surveyor 3, an unmanned lander that had touched down nearly three years prior. Earthly microbes – including those associated with the common cold — were still living inside the camera box.

“The records were good enough to show one of the technicians had a cold when he was working on it,” he said.

Scientists also have evidence that microbes can survive for thousands or even hundreds of thousands of years when frozen on Earth, but surviving that long in space would be an entirely different matter, with the bombardment of UV light and cosmic rays. Then again, the microbe Dienococcus radiodurans is known to survive in the cores of nuclear reactors.

Melosh acknowledges that scientists lack proof that such an exchange has actually occurred between Mars and Earth — but science is getting ever closer to being able to track it down. 

LEAD PHOTO CAPTION: Artist’s conception of an fragment as it blasts off from Mars. Boulder-sized planetary fragments could be a mechanism that carried life between Mars and Earth, UA planetary scientist Jay Melosh says. (Painting by Don Davis. Copyright SETI Institute, 1994)

Source: University of Arizona and an interview with Jay Melosh

60 Replies to “Arizona Scientist: We Could All Be Martians”

  1. RetardedFishFrog said, “We’ve only landed on two planets so far. ” Not to be picky, but we’ve landed on *three* so far: Mars, Luna, and Titan.

  2. “We came from Mars” simply puts off the question of how did life formed in the first place. Though it’s certainly possible, I think people find it more fun as a flight of fancy. Life could have started here as well as on mars – if it came from Mars to here and arose from a single bacteria, we wouldn’t be able to tell the difference!

    Let’s FIND LIFE OR EVIDENCE OF PAST LIFE ON MARS then compare the two before we start theorizing on all this.

  3. It will be much more likely that life is carried to other planets accidentally by space probes from Earth. It would be cool if HIRISE imaged the Viking lander sites and saw a big green patch around them.

  4. i think human can only theorize in accord with his assumption and result of research of founding. meanwhile we have to organize and know the theory will comply with rules of the creator. life could not have originated from any other planets. if it could be this way. why by now we can’t find any evidences of the existence of another life or human like-matter in the universe.

  5. taufan says “why…”

    We’ve only landed on two planets so far. There may be billions more in the galaxy. I’m willing to wait for a larger sampling before coming to any conclusions.

  6. Sounds like Dr. Melosh may have developed a taste for the spotlight. His work on the Moon creating impactor was great work that appears to be solid and has contributed to our understanding of Earth’s history. If he was a contributor to establishing the Cretaceous impact as the cause of dinosaur extinction, then, again, kudos to him. However, microbes from Mars/space is starting to sound like a cry for media attention. Sure, it is remotely possible. However, what is more likely, life came from a rock blasted off another planet that may have had habitable conditions, but maybe not; or that life developed on a planet that manifestly has and has had for a long time conditions that are just right for the formation and propagation of life? Mars may have had great conditions for life at one point. Mars may have developed life. As exciting as I would find that to be, we just don’t know yet. However, it is looking like Mars may not exactly be the Garden of Eden. Earth, on the other hand, is a paradise for everything from simple bacteria (not really so simple) on up to sometimes silly professors. Earth is such a garden spot that life exists in solid rock up to ten thousand feet below the surface.

    I will concede the remote possibility of life coming from Mars. I take the position that is a vanishingly small probability.

  7. Jay Melosh first proposed the “transpermia” mechanisam for exchange of microbes (or nanobes) between rocky planets in the early 1990s. See this copy of a 1994 article by Jay in the Planetary Report:

    That inspired me to write an article for in 1999:
    Your Ancestors May Be Martian
    (does the title look familiar?)

    and I have followed the research of Jay or co-workers since then. In 2001 I wrote:”The long term average transfer rate of 150kg of hospitable rocks per year, with 7% of resident microbes surviving (if any were present in the rocks at the time of launch), is equivalent to a series of space missions that return samples of about 10 kg of Martian rocks each year under protected conditions that are favourable to the survival of any life within the rocks…”

    My personal preference is for life to have originaterd (if it came from our solar system) on a young Venus, which was probably warmer and wetter than Earth or Mars billions of years ago and much more life-friendly than Venus today.

  8. I will agree with Marco a It is hard to believe that we evolved from the smallest of microbes. And then from Mars?? The idea thrills me, but look how adept Humans are to what we’ve got on Earth

  9. Perhaps there is limitless possible places of origin? We may imagine any possible place in solar system, or rather the universe. why Mars, not Venus, Io, Pluto or “Nemesis” or any interstellar Nebula?

  10. It’s more likely that life first evolved on Mars, or maybe even further from the Sun, simply, because that environment cooled sooner.

    Then the impact that created the Moon would have set back chances for life on Earth even more.

  11. For me, it stands to reason that life develops wherever it can, and hangs on for as long as it can, throughout the Universe.
    It seems quite tough and not all that difficult to get started.
    And I also subscribe to the notion that genetic material gets exchanged across space (Panspermia).

    I have no proof of any of this, but nobody else has proof of their notions, either. It’s fun and entertaining to speculate, though.

  12. Oh please, this is not exactly facts based, nor is it very scientific.

    The man looks like a lunatic, his hypotheses are wildly speculative to say the least.


    [life] “It seems quite tough and not all that difficult to get started.”

    Do you honestly think that you could bring a stone to life? Or from absolute nothingness create an entire Universe?

    ..I did, it wasn’t that hard really… I just clapped my hands together and boom, there you go son one Universe extending to infinity in all directions simple really…

    The Universe… not that impressive.. I’ve see it it’s boring. Life? Nothing special really…


  13. A few hundred years in the future, a historian talks to his students.

    You know, in the year 2009 people still believed that Earth was the only planet that had life. And even a few hundred years before that they even believed that the Sun rotated around Earth. We can conclude that those people back then were very arrogant to believe that they were in the center of the Universe but you have to understand that in those days they did not have the technology needed to detect life on distant planets. And even if they had the technology and go to such a planet, they would not have recognized even when it is staring them in their face.

    What they did wrong was assuming that Earth could come from only one place because of their religious believes that limited their thinking prevented them to see that that Universe was filled with life. Luckily some visionaries were not happy with this viewpoint and started to develop technologies that did detect life on distance planets. It took them another 100 years to have real contact with alien civilizations, hunted down, tortured and killed because finding life on other planets was a big thread to local religious powers.

    Luckily we do not live in those times, these were barbaric times.

  14. @tautan, ‘the creator’ lol – if you believe in one creator, why not two, it’s no less irrational. let’s not forget that we’re talking 2-4 billion years, so when your instinct is ‘it’s hard to believe,’ don’t forget that you haven’t evolved to contemplate such enormous time spans and so difficulty ‘believing’ is more of an artifact of your 72-year lifespan than the plausibility of the theory. you have evolved to contemplate 24 hour days, 365 day years, etc. etc. one of the reasons humans believe in a ‘creator’ is because it fits nicely into what we’ve evolved to contemplate.

  15. Sci-Fi Si, a Moon can also be a source of life, especially when it rotates a big planets that might not be able to support life.

    Even life on a gasious planets could evolve, but these are then floating lifeforms.

    I have no doubt at all that life evolves everywhere in the Universe, that is what life does, starting to replicate and grow.

    I do not believe that it will look like us, or has the same chemistry like us. If you look at how many different forms life has on this planet and they all have the same basic DNA structure.

    Oh yes, we also crashlanded on Jupiter, we landed multiple times on Venus and even an asteroid. We crashed on a comet, and probably on phobos too.

    At this time we just don’t have the necessary technology to detect life because we have no clue how alien life would look like. Right now we are searching for Human compatible life, the life depending on water and a certain level of atmosphere and temperature.

  16. However, what is more likely, life came from a rock blasted off another planet

    [life] hangs on for as long as it can, throughout the Universe.>

    Why is it that for some strange reason we will look to anywhere else in the Universe for the origins of life.

    Life was brought to Earth by an asteroid, or life was brought to Earth from Mars, or life was brought to Earth from a brick floating about somewhere in space.

    My grandmother would have called is ‘Looking a gift horse in the mouth’ The ONLY place we know of in the ENTIRE UNIVERSE that we know life to exist is here on Earth. But could life of originated here? Oh no.. It must have come from some crustation floating about somewhere else in the Universe but not here on Earth.

    Couldn’t it just be… and I’m going out on a limb here seeing that there’s ablosutely no evidence to contradict me, that life might just have begun…. on … Earth?

  17. The idea that life could be transferred between planets had been proposed in the past by some brilliant minds, and is plausible and deserves further study. Dr. Melosh has obviously contributed greatly to this “meteor-transfers-life”” theory. Another plausible theory was proposed by a Nobel-winning scientist over 100 years ago – Svante Arrhenius. His theory included electric field uplift of charged bacterial spores, and interstellar distribution by radiation pressure Without knowing about Arrhenius’ work, I stumbled into a very similar theory, that being uplift of charged bacterial spores by electric fields, and interstellar distribution by magnetospheric plasmoids. (see

    All these theories explain why life arose so soon after the Earth became even marginally able to sustain life. All deserve further study. All suggest the near certainty that Mars has life today, genetically related to life on Earth. It perplexes me that these theories would be mocked or ridiculed by anyone not holding a Nobel prize. The book “Imminent Discovery” captures our effort to look deeper into these questions.

  18. This is a delightful discussion. An interesting perspective that I considered, but didn’t include in the story, comes from Paul Davies. Some highlights:

    “Life as we know it appears to have had a single common ancestor, yet, could life on Earth have started many times? Might it exist on Earth today in extreme environments and remain undetected because our techniques are customized to the biochemistry of known life?”

    … July 2007 report by the National Research Council. That report looked at whether the search for life should include “weird life” – described by the Council as “life with an alternative biochemistry to that of life on Earth.”

    “If a biochemically weird microorganism should be discovered, its status as evidence for a second genesis, as opposed to a new branch on our own tree of life, will depend on how fundamentally it differs from known life,” wrote Davies in the Nov. 19, 2007, issue of Scientific American.

    The concept of a shadow biosphere, according to Davies, “is still just a theory. If someone discovers shadow life or weird life it will be the biggest sensation in biology since Darwin. We are simply saying, ‘Why not let’s take a look for it?’

    There’s a press release for more information here:

  19. Suppose that life is so abundant and can form so easily that even Novas and Supernovas can not erase it…….. And that the power from the explosions may send these living cells out as a dandelion flower that has seeded and the wind carries them to other places. Just seems to me that it shouldn’t be phenomenal occurrence but rather a fairly natural event.

  20. @Yael Dragwyla+Olaf
    For the record, I was counting planets we have landed on: Mars and the Venera missions to Venus. I don’t count ditching Magellan into Jupiter as landing on a planet.

    Life certainly could start on a moon such as Europa, Ganymede and perhaps Titan and Enceladus.

    My point in response to taufan is that we have only begun to start looking for life on other worlds. It’s much too early at this point to say that life on other worlds must not exist because we haven’t been able to find it yet.

  21. Sci-Fi Si – “Couldn’t it just be… and I’m going out on a limb here seeing that there’s ablosutely no evidence to contradict me, that life might just have begun…. on … Earth?”

    Yes it could be like that, so we need other tests to confirm that it could not have come from another source.

    But first we have to discover possible other sources and test those theories too.

  22. Good point Olaf! It is far more likely that Earth life started on Earth and not Mars. It is certainly just as likely to have “seeded” in space, “pollinated” the Earth, and evolved from there. Until we learn more of the evolution of life it’s only speculation where it all began. But it’s a lot of fun to speculate, don’t you think?

  23. I agree RetardedFishFrog, once we have found hundereds of Earths and find no evidence of life on it, then we could say that life as we know it is unlikely.

    But so far we have not the technology yet to find these Earths so wa cannot say that only on this Earth life exists.

  24. He’s still touting the myth that Apollo 12 brought back a microbe that had spent 2 years on the Moon inside Surveyor 3.

    They now think it was from contamination during the examination of the returned Surveyor parts on Earth.

    And now I know what Santa does in the off season!

  25. Oh wait – Melosh did dispute it.

    The article says otherwise though. Looks like some sloppy writing/editing there.

  26. I agree neoguru, I love speculating and dreaming that there is full of life out there.
    But if it is not, then it is not, I won’t lose my sleep over it, but it would be very cool.

    The fact that someone says that it should conform to a creator makes me nervouse on a science site. First of all with creator? The Flying Spaghetti monster? And secondly what if it does not fit, should we destroy all evidence that contradicts the so called creator?

  27. My knowledge is that there were indeed micorbes in the camera of the surveyor that was bought back by Apollo 12. that survived, but not reproduce during the time on the moon.

    But we will seen more evidence about this when they do more experiments with the new Moonlanding coming up.

  28. There is nothing in either science or religion that denies that there is life on other planets. Science is waiting for conclusive proof. The Bible, for example, is completely silent on the matter, as are the books of most major religions. Some, such as Scientology and the Mormons insist upon life existing elsewhere. Given the non-special status of Earth, the ubiquity of the same elements in the universe, and the shear size of the universe, it almost defies logic that there is no life elsewhere. We just haven’t found it yet. That said, I expect that it will arise more readily on planets/moons/bodies within certain zones or regions in space. It is also more likely to thrive on a garden spot type planet. Could there be or have been life on Mars? Sure. We haven’t ruled it out. Other than a few miniBigfoots and a few wooden planks, we have not found any proof yet. Earth is perfect for life. Why come up with some Rube Goldberg scheme to get life here in some pansgermia event rather than believe that life arose on a planet perfectly suited for life to arise on. Occam may have something to say about this whilst employing a razor.

  29. Perhaps Mars microbes came to Earth, which already had native life on it, and they duked it out Darwin-style.

    Venus could have joined the party too.

  30. Olaf, you are just remembering what everyone thought about that story since those microbes were found. Since then, it has been better determined that they came from some technician examining the Surveyor 3 parts.

    Unless you have some kind of first-hand evidence we don’t know about.

    Earth life may have been started and wiped out many times in the very early days of the Solar System, when our planet was being bombarded by huge space rocks. So the creatures we have descended from may not have been the first.

  31. This is a vast conspiracy to deflect from the coming great awakening of consciousness in the year 2012. NASA is behind this sinister plot. Do not believe their lies about perchlorate. We are not martians. We are unenlightened Earthlings.

  32. Life comes from everywhere. The seeds of life rain down on all planets and they all exchange material constantly over the eons. So when these materials are in the right place and time, the right type of planetoid all that, then life begins.
    Life blooms all around us in the universe, we can’t prove it yet but the time will come, its inevitable. Its silly to say its from one tiny world or another. Microbes probably routinely rides debris back and forth to and from every world imaginable, just cannot bloom into complex life unless its in the right conditions – aka Earth.

  33. re: Arik Rice’s point, I think it’s more likely all life on our earth came from a single cell event, since in all life forms studied 3 base pairs code for a unique amino acid, and it’s always the same one. DNA transcriptase from a human, an oak tree or a bacteria will read a given clip of DNA the same way. No need to suppose that martians would necessarily use the same nucleotides, or if they did that the code would translate to the same amino acids.
    If there were a second viable cell around at the time the first one came together, wouldn’t some animals or plants use one code and others use a different one? /

  34. Nice idea, sadly there is little if any evidence to support it. Have we found microbes or evidence for them on mars itself yet. Why does the existence of microbes on Earth mean they have to have come from another planet, a planet that has no evidence of microbial life.

    It’s a good idea for comic books but in reality it’s a little far fetched. On the other hand, if they do find microbes on Mars, what is the bet they came from Earth? The impact thing works both ways right ? You could have microbes coming from Earth and raining into Mars. This event is far more probable than the Mars seeding Earth event.

  35. If life once came from Mars then life should also try all the day long to spread itself from earth! From earth, across all the rest of the solar system. All the day!

    Mars should once have been a fertile place for genetic material, if the rare events of ejection with escape velocity might have transported “sources of infection” not only into interplanetary space, but also to a tiny spot named Earth, injecting Earth with fertile instead of futile rocky bio-carriers.

    Therefore, if the panspermia theory holds true, we should on the other hand also detect frutile material from earth in every corner of this solar system.

    “Our” microbes should also be “outdoors”, if the theory of life from Mars holds true!

  36. It is common knowledge that our geninome
    is not pure? By now we have established,
    that our genome is an mix, ergo this manipulation of the genome code must have been done by a superior induvidual, which we
    currently have no knowledge of! The question
    really is, WHO did had that knowledge to create a HUMAN? At least that is what we call our self? We are at this point, that we are comparing the “HUMAN” genome with that of
    other spiecy’s on this planet and early indications are that we are related with them
    on the genome level? So what does all this means? Well my thought’s are that it was not an accident nor an random act it is to complicated for either one! That leaves us
    with the possibility that we had visitors?
    There are faint records of that possibility, but
    even if, the immensity of manupilation of tempering with so many genome varriaties is
    mind blowing and the fact that it took some
    generations to develop which implicate that
    the visitors must had an long life and stayed
    a while? If we consider that a “HUMAN” is a
    “near” perfect chemical factory, ask any doctor
    how well this self sustainable factory of a human body is and so I still have a hard time
    in believing that it was an accident? Ergo this
    leaves the possibility of creation to a likeness
    of a being but where did they came from and
    why us? Darwin has stated the obvious because it is in the code of the genome, all
    live formes are coded to develope albeit each
    in its own way including “HUMANS”

  37. Yes it’s possible although there is no evidence for it, scientific or otherwise.

    But science isn’t about possibility.

    Imagination is about possibility; science is about what is.

    It’s also possible that Venus was a comet Phaeton that disturbed the orbits of the solar system and caused a catastrophic meteor shower, conflagration, and deluge but saying so causes fundamentalists to start drooling and frothing at the mouth.

  38. Genetic code is extremely complex and comprehensive and must have taken considerable time to evolve. It might have evolved prior to the origin of the solar system itself. As the solar system has been gifted with the wide range of elements in the periodic table other than Hydrogen and Helium in the core of our star, the basic signature of life may also have been similarly gifted to us.

    Biological exchange between not only planets but between various past and present star systems is very much probable.

    The extent of development of life probably depends upon the environment that the genetic code finds itself in. By this logic Earth is the most likely candidate in the solar system to have captured and propagated this code rather than receiving it through other planets in the solar system.

    However, this guess is on the basis of what we are seeing today. Perhaps the conditions might have been more conducive on Mars and even on Venus compared to Earth in the distant past. It is probable that life might have taken a root in these places and then found a better environment to thrive on Earth.

    It is less probable to imagine that life originated from scratch on Mars and then came to Earth.

    In the future when a catastrophe strikes planet Earth it is possible that a good chunk of bacterial life with the genetic code shall be ejected out into interplanetary or even interstellar space. The bigger the impact the more distance it will travel taking the genetic code to safety. For a small impact some of these chunks of rock will fall back to the Earth itself bringing back the seeds of life to flourish again after the bad times are over. When the impact is so big that the life cannot flourish again, the rocks would have momentum to leave the solar system and try to hunt another place to settle!

  39. Anne, here are the two paragraphs in question. The first one says scientists did find microbes in the lunar lander robot that had been on the Moon for over 2 years. The second one quotes Melosh saying otherwise it was someone examining the Surveyor 3 equipment after the Apollo 12 mission who accidentally put the bugs there.

    You tell me how I am to interepret this:

    Surveyor 3, an unmanned lander that had touched down nearly three years prior. Earthly microbes – including those associated with the common cold — were still living inside the camera box.

    “The records were good enough to show one of the technicians had a cold when he was working on it,” he [Melosh] said.

  40. Mars is the closest body with the most potential to have had life. It’s about the chances of material exchange based on what we know so far about our solar system. I don’t think anything has been ruled out. Comets and other bodies from the edges of the solar system are thought to be potential sources of biological building blocks.

  41. Bravehart – “It is common knowledge that our geninome
    is not pure? By now we have established,
    that our genome is an mix, ergo this manipulation of the genome code must have been done by a superior induvidual, which we
    currently have no knowledge of!”

    According to percisely who us this common knowledge?
    And How do you know that this common knowledge is actually true?

  42. “# LLDIAZ Says:
    February 23rd, 2009 at 9:15 am

    why is it always Mars?
    We couldn’t have come from somewhere else?
    Somewhere deeper in space..”

    I agree. Why not Martian microbes coming from Terrestrial or Venusian origins. Venus was warmer and likely had global oceans; add in a huge volcano from Aphrodite Terra and “ka-pow” life springs into existence on Venus…. not that I’m actually seriously suggesting this scenario.

    I suspect that Terrestrial life popped into existence right here on Terra Firma (Terra Aqua?) and has been multiplying and mutating away for æons.

  43. I’m still convinced that Zecharia Sitchin’s ideas are the closet to the truth. It just makes good sense. 🙂

  44. Huygens:

    evidence … surviving a few years in space … three years prior … still living

    All terms suggesting that the microbes had survived a few years in space and were still living when the camera was inspected. I’m sorry you’ve had so much trouble with those two paragraphs, and I hope this helps.

  45. I think the jest of what Jay Melosh is saying is that we could be from another planetary body, I think we all could say that is possible, but we need to research this more.

    I think the planetary society are testing this theory out in an upcoming launch to Phobos.

    As Alex was saying that this is not old news, sure that is correct and it just goes to show you that ALH84001 may indeed harbour fossilized proto-bacteria, all in all this is exciting stuff.

  46. So, life, water and everything else seems to have come from somewhere else.

    Why are these people refusing to accept the possibility that water, carbon and the other elements required for life existed on earth from its formation?

  47. I am convinced that Zecharia Sitchen is a well paid disinformation agent working for the House of Rothschild to deflect any investigation into the fiction that Moses led slaves out of Egypt and that the AskeNAZI brach of Judaism are not Semitic! Sitchen would want you to think that the reason for the looting of the Bagdad Museum was to cover up the Annunaki “creation”, but it seems more likely that there was much proof that the Old Testament was a mixing of Egyptian and Babylonian mythologies.

  48. By your command, BJ!

    Earth has so many fabulous and varied ecosystems, harbouring every kind of life. We still have NO idea how life began but have proven that in almost any environment, the basic building blocks of life assemble almost automatically. (nice to hear for people who like a little company in the cosmos!) So as long as that first spark was here, and lord (small L) knows, we gots lots of sparks, then for absolutely sure, our earth would have made the most out of that possibility and encouraged the flourishing and abundance we see today. No need for extraterrestrial help, No need for meteorites and seeding. Life is here. Life did not start as an intelligent alien, but fossil records show that it started very modestly. That would indicate it started here, as a very basic model. That’s why every bacteria is my buddy.

  49. Peter – a fossil record of very basic life forms is also consistent with life on Earth being the result of bacteria that have been delivered here through space, either by a meteor or some other method. And watching the basic building blocks (amino acids) assemble from the right ingredients (like Urey did 50 years ago) is light years away from having a reproducing life form self assemble. Science hasn’t even gotten close to figuring out how this could happen. So did it take millions of years, or billions of years, for life to form? If the answer is billions, then the fossil record shows there wasn’t time on Earth – so it happened someplace else. And can bacteria survive space? Not all – but it only takes one bacteria to start life on a planet. Scientists have got to have open minds when considering this question.

  50. The earlier Edicarian Biota may (repeat may) show that evolution started twice on the Earth. This biota pre-dated the Cambrian explosion, and has no direct lineage to life forms today.

    Or, Maybe Edicarian biology was the “original” life on Earth until it was displaced by Martian lifeforms creating the Cambrian Explosion 542 Mya.

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