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Space Science

Comets Probably Seeded Earth's Nitrogen Atmosphere 110

Posted by samzenpus
from the in-the-beginning dept.
KentuckyFC writes "One of the biggest puzzles of astrobiology is the origin of the Earth's oceans and atmosphere. One favored theory is that our water is the leftovers from a bombardment of comets early in Earth's history. But the ratio of hydrogen and deuterium in the oceans doesn't match the ratio in the four comets measured so far (Halley's, Hyakutake, Hale-Bopp and C/2002 T7 LINEAR). Now a new analysis of the ratio of nitrogen-14 and 15 isotopes in these comets and on Earth places new limits on how much of our environment could have come from comets. On the one hand, the astronomers who did the work say that no more than a few percent of Earth's water could have come from comets. But on the other, they say that the ratio of nitrogen isotopes in these comets almost exactly matches the ratio in Earth's atmosphere. That suggests that while Earth's oceans must have come from somewhere else, Earth's early atmosphere was probably seeded by comets."
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Comets Probably Seeded Earth's Nitrogen Atmosphere

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  • by eldavojohn (898314) * <eldavojohn.gmail@com> on Thursday July 02, 2009 @12:00AM (#28553773) Journal
    Recently I submitted a story [slashdot.org] that's probably not going to be published that claims:

    Space.com brings word of a team using new evidence is suggesting that the mysterious 1908 event in Tunguska was a comet [space.com] despite a team two years ago arguing it was an asteroid [slashdot.org]. The comet theory does explain the odd phenomenon of the night skies being lit up for several nights following the event all across Europe--about 3,000 miles away. Researchers believe this points to a comet because when the space shuttles launched today pass through the atmosphere they cause or improve the formation of noctilucent clouds [wikipedia.org]. These clouds are so high up (55 miles) they are only made of ice particles and they are only visible at night which gives researchers reason to draw the conclusion that the 300 metric tons of water vapor that the shuttle pumps into the Earth's thermosphere must likely indicate that the thing that hit was loaded with water or ice. This would make it a comet and not an asteroid. This--of course--raises new upper-atmosphere physics problems for the Tunguska event but explains the strange phenomenon over the skies of the world following it. You may remember analysis of Lake Cheko last year [slashdot.org] in an effort to better understand what happened.

    Well, if every comet that hit earth dropped off a little bit of water--even in the form of noctilucent clouds ... it'd take a while but is it really so far fetch to think that ultimately all our water and atmosphere are extra-terrestrial? Probably unlikely but over a long enough time, who knows?

    • by khayman80 (824400) on Thursday July 02, 2009 @01:04AM (#28554029) Homepage Journal

      ... it'd take a while but is it really so far fetched to think that ultimately all our water and atmosphere are extra-terrestrial?

      The point is that the isotope abundances of the oceans don't match the only four comets that have been observed precisely enough. H20 and HDO are easily distinguished from each other, and deuterium (the "D" in HDO) is quite stable so the isotope abundances shouldn't have changed. We've only measured 4 comets, though, so perhaps other comets more closely resemble our oceans.

      Coincidentally, I attended Dr. Goldblatt's fascinating talk at the Fall 2008 AGU conference where he showed that the faint young sun paradox [dumbscientist.com] could be mitigated by a higher nitrogen pressure in the primordial atmosphere. Someone in the crowd (a Slashdot user, perhaps?) answered my question about experimental constraints on this pressure by saying that current research involving "raindrops" might produce a constraint soon.

      This paper seems like it should be relevant, but I've yet to see a direct connection. If anything, the disparities in the isotope abundances between 15N/14N and D/H seem to imply their origins are (at best) only loosely connected. But unfortunately the guy who shouted "raindrops" didn't have a microphone and he was across a crowded lecture hall, so I don't have the foggiest idea what he meant. Maybe "raindrops" was a brief reference to the "enstatite chondrites" on page 7 of this new paper (the context seems similar, at least). However, Javoy's paper was published in 1986 and my mysterious benefactor definitely said the research was currently underway. Plus, the topic at the time was the total pressure of nitrogen, not the isotope abundance...

      Anyone who knows about this subject, please enlighten me!

    • Well, if every comet that hit earth dropped off a little bit of water--even in the form of noctilucent clouds ... it'd take a while but is it really so far fetch to think that ultimately all our water and atmosphere are extra-terrestrial? Probably unlikely but over a long enough time, who knows?

      I think that the point of the summary is that if the water were primarily from comets then we'd expect the water on earth to have a similar ratio of deuterium to hydrogen to that found in comets. Since it doesn't, either most comets out there have a very different composition from the ones we've observed, or the earth's water must have a different source. Of course the water is extraterrestrial in origin (like everything else), but it looks as if we didn't get it from comets.

    • by Phoghat (1288088)
      This is why it's a Theory
    • IANAAP/AB:

      IT seems pretty clear the water we have today didn't come from the type of comets we see NOW. However, I don't see how it says anything about what sources of water ice were like shortly before or after the sun spooled up it's furnace, and gradually blew the remnant dust to the edge of the solar system. Why couldn't the proto-Earth cloud have captured large volumes of water ice before the Sun fired up?

      As for the Nitrogen. That the isotope ratios in the comets and on the Earth agree, means to

  • by rattaroaz (1491445) on Thursday July 02, 2009 @12:16AM (#28553843)
    Nitrogen came from comets, and methane came from Uranus.
  • ... how could anyone reasonably think that comets brought it all?

    • Re: (Score:3, Funny)

      by socsoc (1116769)
      Duh, it reproduced once it arrived on Earh.
    • Re: (Score:3, Interesting)

      I was under the impression that the Earth's water precipitated out of the original accretion disc as the early earth cooled. That is, everything accreted, and then as the molten rock and surrounding gases cooled to form a sold surface, the water that became the Earth's oceans and such also cooled and condensed, and basically rained down on the planet over time.

      Has there been some reason to doubt this? i.e. evidence that refutes this hypothesis?

      • Re: (Score:3, Interesting)

        by Nutria (679911)

        It's easy (unless you're a fundie) to understand where the heavier elements and such come from, since they melt at high temperatures.

        But water and the "stuff" that are gases at STP are volatile. So... what kept them "near" the earth while it was very hot (way past the boiling point of waster) and small and accreting? There wasn't enough of a magnetosphere to protect any atmosphere.

        Could it be that H2O, N2 and O2 were created from the decomposition of very hot rocks?

        • by RockDoctor (15477)

          Could it be that H2O, N2 and O2 were created from the decomposition of very hot rocks?

          By the time that you've got your rocks molten, their water, CO2 and ammonia (nitrogen in it's most-likely protoplanetary form) would have pretty-much fucked right off. At the time that the Moon was formed (giant impact hypothesis, still the best one running), much of the depth of the mantle was temporarily ejected into low proto-Earth orbit, and at sufficient temperatures that significant amounts of such volatile ions as s

    • by Kupfernigk (1190345) on Thursday July 02, 2009 @03:29AM (#28554793)
      The answer to your question is, because the way the planets arose is slowly getting elucidated and it is a lot more complicated than anybody used to think. One very important concept is the "snow line" - the distance from the Sun at which ice can form. A build up of icy objects around the snow line followed by gravitational disturbances could result in the transport of large amounts of ice in both directions - inwards and outwards. Then the gravity well of accumulating planetary masses does the rest.

      This is a rapidly evolving field and I don't pretend to have more than a very casual reader's knowledge - but think of it like this. The Earth is, in cosmic terms, a small planet. Its water layer is a minute fraction of its mass. In terms of the solar system as a whole, the percentage of the available water on Earth is extremely small.

  • by comet63 (1256400) on Thursday July 02, 2009 @12:19AM (#28553863)
    The article notes that the ratio of the nitrogen isotopes matches what is in the earths atmosphere. It seems to me, that just makes it possible that the comets are a significant source of the nitrogen on Earth. It is also possible that the nitrogen in the comets and in the atmosphere came from a common source.
    • Agreed, Correlation does not equal causation.
      • This is a comparison, not a correlation.

        • by Sobrique (543255)
          Comparison isn't causation either....
          • by Sockatume (732728)

            Nobody's saying it is, the article is putting an upper bound on the amount of water and nitrogen that could come from cometary ices. They comment that this leaves the door open for a substantial amount of nitrogen from comets, but only a miniscule amount of water.

    • Re: (Score:3, Interesting)

      What comet63 said. Large primoridal clouds of hydrogen are easy to understand, and oxygen is enough lighter than carbon that it could occur early on in stellar formation, I'd think (IANAAP, IMBFOS). So I can imagine large clouds of the two gases igniting in the early part of our planetary history, with enough being captured by our own gravity well to compress and become water. The rest, as they say, is geography. Add lots of the slightly less reactive nitrogen and you'd get something approaching the mixt

  • In addition to creating an atmosphere on earth, comets may also have seeded life [bbc.co.uk].
  • Comets Probably Seeded Earth's Nitrogen Atmosphere

    So we've been breathing space spooge all along?

    Well THAT explains a lot...

  • No, no (Score:2, Funny)

    by djconrad (1413667)
    Everyone knows nitrogen is here because of the Holy Sauce dripped from His Noodly Appendage.
  • Obvious? (Score:1, Informative)

    by muphin (842524)
    Although comets may have initiated seeding of life and the foundry of everything from water to minerals .. there has been proof that water is abundant in space and maybe have just been absorbed into the atmosphere on earth and generated that way, over time rain would have brought the water molecules to the surface.
    http://www.space.com/scienceastronomy/astronomy/milkyway_water_010412.html [space.com]
  • Hydrogen probably came from:
    • solar wind, and
    • primordial disc hydrogen.

    My guess is that earth started out as a (not -so-giant?) gas giant and bled of most of it's original hydrogen. If that's even vaguely true, then there's little likelihood that the isotope mix would be anywhere near what's in comets.

    I'm guessing that the deuterium mix is much higher than in comets (because deuterium, being heavier than hydrogen, is less likely to bleed off).

    • Are you an astronomer? I ask only because you're modded +4 Interesting. But, in your comment you say: "My guess is..." and then "I'm guessing that..." What makes you think that your two guesses are in any way valid? Maybe this (my) comment is directed more at the mods than you because if you were not modded up so much I'd gloss over your comment.

      • by TheTurtlesMoves (1442727) on Thursday July 02, 2009 @02:27AM (#28554461)
        By your reasoning only economist should comment on topics of economy, climatologists on topics of global warming, etc...

        This is /. you are allowed to speculate and the reader shouldn't be such an idiot to assume every post is by an expert or a lawyer (IANAL crap).

        Even more important experts can and should be questioned. People outside the field can give suggestions and should criticize experts if they cannot justify their point of view. The only times we get a group of people that think they cannot be questioned by outsiders... they are usually wrong.

        And what are your credentials? Modding expert? Modding consultant?

        By the way I am an astronomer by training... Grandparent has a good point.
        • He does? I've never heard a theory that the rocky planets started out as gas giants.
          • Well you have now and at least one astronomer thinks he has a point.
          • No --He even said no-so giant. A lot of the original hydrogen now locked up as water could have been hydrogen from the proto planetary disk. It did not need to be water in the first place. After all most of the sun is just H2. As I said, he/she had a point. Not that all of it is correct as we understand.
            • Liar. What he wrote was a (not -so-giant?) gas giant . The bit in brackets is optional, but with it makes absolutely no fucking sense at all - a not-giant giant?
        • by db32 (862117)

          The only times we get a group of people that think they cannot be questioned by outsiders... they are usually wrong.

          What does government have to do with this discussion?

  • just about anything in the universe, and specifically various aspects of this planet, is becoming more like numerology than anything else. Case in point:

    But on the other, they say that the ratio of nitrogen isotopes in these comets almost exactly matches the ratio in Earth's atmosphere. That suggests that while Earth's oceans must have come from somewhere else, Earth's early atmosphere was probably seeded by comet.

    Any pattern they find seems to make scientists believe something is true, no matter how improbable. Scientists are only seeing what they want to see in this data. Despite this method of guessing based on simply "interesting patterns" and hoping they are right, these very same people consider taking on faith what the Holy Bible says about the origins of the

    • by alexhard (778254) <alexhard@@@gmail...com> on Thursday July 02, 2009 @01:51AM (#28554273) Homepage

      >method of guessing based on simply "interesting patterns"

      That would be the SCIENTIFIC method (or at least the first part of it), the source of all scientific advancement since whenever.

    • Re: (Score:3, Informative)

      by ceoyoyo (59147)

      Carefully note the words "probably" and "suggests."

      In other words, nobody has claimed anything is "true." They noted an interesting pattern and thought about what it could mean. Now they'll try to devise experiments to test that hypothesis.

      Contrast this with theological reasoning: "the bible says so, therefore it is true. End of discussion."

      • by glitch23 (557124)

        Contrast this with theological reasoning: "the bible says so, therefore it is true. End of discussion."

        Scientists are free to prove the Bible right/wrong. The problem is they do not. Why do they not even try? Are they afraid that they will prove it right?

        • Re: (Score:3, Insightful)

          by ceoyoyo (59147)

          How do you prove a story wrong? Particularly a vague, self contradictory story? Many of the things we know about the world appear to contradict what's in the bible. Bible advocates either twist bible stories so the apparent contradiction goes away, or they simply ignore the science.

          I notice you didn't even try to reply to the content of my post, but rather cooked up some extremely questionable claim that you stated as fact, instead. Typical.

  • by icebike (68054) on Thursday July 02, 2009 @01:03AM (#28554025)

    The theory of comets as a source of water was also published in 1990, by Louis A. Frank.

    Not exactly your average crack-pot scientists, Frank was the designer of something like 13 payloads on various launch vehicles in the 80s and 90s.

    Frank posits that that small comets still hit the moon and earth almost daily, delivering water virtually every day. These small comets are more like fluffy snowballs, and are small enough not to have much if any radar signature, but their effects upon impact with the atmosphere are visible from above.

    http://en.wikipedia.org/wiki/The_Big_Splash_(book) [wikipedia.org]

    Excerpt from The Big Splash
    by Louis A. Frank with Patrick Huyghe
    Published by Birch Lane Press, 1990.
    ISBN 1-55972-033-6

    http://smallcomets.physics.uiowa.edu/blackspot.html [uiowa.edu]

  • Ramen! (Score:2, Funny)

    by bazorg (911295)
    I can easily picture the Flying Spaghetti Monster lobbing comets around ...
  • what happened to the dept tag?
  • I find these stories kind of unfulfilling. No matter how far we get back in nature's cause and effect, I'm still left thinking 'what came before that'. When scientists finally discover the root of all creation, I'll still be thinking the same thing.
  • to believe in some of these theories....

    • by radtea (464814) on Thursday July 02, 2009 @09:20AM (#28556671)

      Faith in what? Have you read the paper behind this idea? It's full of assumptions and caveats that are explicitly laid out by the authors, pointing out that one can follow a particular thread of plausible but unproven argument, and suggesting ways of empirically testing it.

      Ideas are tested by experiment and systematic, often quantitative, observation. That is the core of science.

      Ideas are believed without question. That is the core of faith.

      See the difference?

  • they say that the ratio of nitrogen isotopes in these comets almost exactly matches the ratio in Earth's atmosphere. That suggests that while Earth's oceans must have come from somewhere else, Earth's early atmosphere was probably seeded by comets.

    Or the nitrogen in the comets and the nitrogen in the Earth's atmosphere had a common origin which seems much more likely, the story title notwithstanding.

  • This is only a puzzle if you come from a particular worldview.

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