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Earth Science

Lack of Molybdenum May Have Delayed Life on Earth 89

Posted by samzenpus
from the we-would-have-started-sooner-but dept.
esocid writes "Scientists from around the world have reconstructed changes in Earth's ancient ocean chemistry during a broad sweep of geological time, from about 2.5 to 0.5 billion years ago. They have discovered that a deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth for nearly 2 billion years. Bacteria cannot fix nitrogen efficiently when they are deprived of molybdenum. And if bacteria can't fix nitrogen fast enough, then eukaryotes — a kind of organism that includes plants, pachyderms and people — are in trouble because eukaryotes cannot fix nitrogen themselves at all. Ariel Anbar, a co-author of the research of Arizona State University, stated that "eukaryotes depend on bacteria having an easy enough time fixing nitrogen that there's enough to go around. So if bacteria were struggling to get enough molybdenum, there probably wouldn't have been enough fixed nitrogen for eukaryotes to flourish.""
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Lack of Molybdenum May Have Delayed Life on Earth

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  • by pintpusher (854001) on Wednesday March 26, 2008 @08:29PM (#22876364) Journal
    This casts an interesting light on the idea of terraforming. There's often been the idea that we could just introduce plants into a CO2 rich environment and in pretty short order we'd have a breathable atmosphere. Apparently that may not be the case. Without an oxygen rich environment to free the molybdenum, there's no significant nitrogen fixation and thus those plants are going to be hurting pretty quickly.

    Also, this makes me wonder what those eukaryotes were doing for the first 2 billion years. Were they undergoing all sorts of genetic mutations that primed them for takeover once the situation changed? IOW, I wonder what would have happened if this little molybdenum problem had resolved earlier. Would the eukaryotes continued to flounder (pun!) because of a lack of genetic diversity? Or would they have just as rapidly developed putting the current day well into the cockroaches-rule-the-earth epoch?
    • by tgd (2822)
      For what its worth, I don't think there's often that idea among plant biologists.

      • I'm sure you're right. I'm speaking more about my more-or-less common man image of terraforming... at some point natural processes take over and the whole "just works". But the need for free molybdenum to support nitrogen fixing sort of throws a monkey-wrench in that idea.
        • by tgd (2822) on Wednesday March 26, 2008 @09:02PM (#22876638)
          Well, I'm no biologist but right off the cuff I think there are some problems with this "theory"... it makes an assumption that in an environment without fixed nitrogen that complex life would not have evolved to either not need it or to do it itself. It also assumes that the availability of molybdenum is required to fix nitrogen.

          The fact that eukareotes did not evolve it doesn't mean they couldn't have -- it just means that their environment they evolved in didn't need that ability, likely because prokaryotes evolved it already. (Or they didn't actually originally need it -- which may make more sense because if one assumes that that evolution was necessary for eukaryotes, and they evolved from prokaryotes, then how did they *lose* that ability?)

          Again, not a biologist but the critical reader in me gets a "I have a hammer, so everything is a nail" vibe from this theory.
          • Well, I'm no biologist but right off the cuff I think there are some problems with this "theory"... it makes an assumption that in an environment without fixed nitrogen that complex life would not have evolved to either not need it or to do it itself. It also assumes that the availability of molybdenum is required to fix nitrogen.

            I'm no biologist either... all the more reason for us to get really nasty and get a right proper flamefest going!! ;-P

            So, there are certain rules to the chemistry that underly biology and (really really speculating here... in fact this whole thing is just speculation on my part, sort of a beer-guzzling approach to science discussion) maybe it's possible that one really *does* need molybdenum to fix nitrogen with any efficiency. That gives evolving life two choices (it seems I'm repeating you here)--

            1. stru

          • by dokebi (624663) on Wednesday March 26, 2008 @09:47PM (#22877020)
            Nitrogen is part of both DNA and amino acids. Therefore all life as we know it requires it. We can speculate about other types of lifeforms that doesn't use DNA, but as far as we know the, nitrogenases are the only enzymes that takes nitrogen gas to a usable form (ammonia).

            It is important to realize that life on earth didn't all come to existence at once. Animals cannot breath CO2 not because it can't evolve for it but because our metabolism depends on oxygen. Without plants fixing CO2 and putting out O2, *for millions of years*, animals couldn't exist. Plants couldn't evolve to fix nitrogen in the similar way. Read up on the nitrogen cycle.

            BTW, IMAB (I am a biologist).
            • by debatem1 (1087307)

              BTW, IMAB (I am a biologist).

              IANAEM (I Am Not An English Major), but wouldn't that be "IAAB"?
            • Re: (Score:3, Interesting)

              by icebike (68054)
              > Read up on the nitrogen cycle.

              I did. and molybdenum was not mentioned anywhere.
              • Re: (Score:3, Informative)

                by thepotoo (829391)
                Sigh. [google.com] How hard did you look, exactly?

                (Mo is used as a cofactor, meaning that it can be used over and over again without being depleted. You just need a single atom of Mo per enzyme.)

              • TTW: (Try the Wikipedia) http://en.wikipedia.org/wiki/Nitrogen_fixation [wikipedia.org]
                • by icebike (68054)
                  But the only reference to Molybdenum in that wiki article was
                  to a artificial process discovered in 2003, NOT to natural fixation.
                  • But thats exactly what the original was about: Molybdenum plays a significant role in the nitrogen cycle. The artifical compound for nitrogen fixation shows that it is possible to use Mo for that. And since the ligand in the compound by Cummins et al. bounds with N-atoms to the Mo, it would be easy for "mother nature" to use proteins for that.
            • by LWATCDR (28044)
              Oh come on there is no proof that nitrogen is needed complex life. Just because every known life form on earth needs doesn't mean that it is required.
              BTW yes I am just kidding.
              Thanks for your post. I loved science but never really got into biology. Probably because the required biology classes in high school and college where mainly what I called "gross plumbing" classes.
              I did like Chemistry so I have to admit that I get a chuckle out of it when people make a statment like. "Maybe life could just use someth
    • by AJWM (19027)
      Also, this makes me wonder what those eukaryotes were doing for the first 2 billion years.

      Mostly "not existing". Eukaryotes didn't appear until around 1.5 to 2 billion years ago -- about 2 billion years after prokaryotes arose.
      • From TFA:

        Knoll was perplexed by the fact that eukaryotes didn't dominate the world until around 0.7 billion years ago, even though they seemed to have evolved before 2.7 billion years ago.
        in other words, they appear to have been just lying around for 2 billion years.
    • Without an oxygen rich environment to free the molybdenum, there's no significant nitrogen fixation and thus those plants are going to be hurting pretty quickly.

      There is significant nitrogen fixation from lightning, currently thought to be over 5% of the natural total. This is well known, and I'm sure the authors of the paper are aware of it. The article states that a low level of nitrogen fixation favors prokaryotes, but it's unclear if this is just generally true in a low nitrogen environment, or if only nitrogen fixing bacteria are thought to have thrived when the level of molybdenum was low.

      • This is interesting and thanks for it!

        But what is the advantage to learning how to fix nitrogen if there is already sufficient amounts around? Clearly, the amount that is fix(ated?) by lightning (and other non-biological processes??) is not sufficient to to support the kinds of nitrogen level needed for serious eukaryotic developement. At least that's how I read it... reiterating that I'm not a biologist, just curious.

        And it's not clear to me at all that only nitrogen fixing bacteria thrived when the molybd
        • by thepotoo (829391) <thepotoospam AT yahoo DOT com> on Thursday March 27, 2008 @08:29AM (#22880344)

          But what is the advantage to learning how to fix nitrogen if there is already sufficient amounts around?

          It's all about evolution. Sure, you* have enough NH3 to survive, even to grow, but there's millions of tons of N2 gas in the atmosphere, and if you could somehow use that as a fuel source, you'd be set for life.

          So then, along comes a random mutation in an enzyme that pulls converts nitrites to nitrates (I'm making this up - but it was probably some enzyme to do with N). Rather than killing you, it allows you to pull N2 out of the air and turn it into ammonia, allowing you to reproduce more quickly. Now another mutation comes along, and it allows you to use Mo to push forward the reaction (mind you it worked before you had Mo: reactions can generally go forward without their cofactors, just more slowly.)

          With this cofactor, you're able to reproduce much more quickly than your neighbors which don't have the mutation, and you become the bacteria we know today.

          *you here refers to a now-extinct progenitor of nitrogen fixing bacteria. Individuals reproduce, populations evolve.

          So maybe it was mostly nitrogen fixers around, but they weren't doing very well because of a lack of molybdenum?

          Like I said, cofactors generally speed up a process. They are not generally required for the reaction to happen, they just speed it up (by several orders of magnitude) when they are present.

      • Lightning in a reducing atmosphere (like Titan's) would produce ammonia. Lightning in our atmosphere produces nitrogen oxides, which combines with water to produce nitric acid. So the fixing follows a very different path.
    • by HonkyLips (654494)

      Also, this makes me wonder what those eukaryotes were doing for the first 2 billion years.

      If you really want an idea, try reading "Oxygen" by Nick Lane, basically it's a popular science book which looks at recent research into the evolution of the Earth. It's very interesting and overturns a few established ideas, such as the "mass extinction" of anaerobic microbes as oxygen entered the atmosphere. I got it as a bonus when I bought his other book "power, sex, suicide" which looks at mitochondria and cellular evolutiuon too, and actually found it more interesting.

  • 42 (Score:5, Funny)

    by RuBLed (995686) on Wednesday March 26, 2008 @08:31PM (#22876382)
    Its the ultimate answer to life and everything.

    According to wikipedia.

    Molybdenum is the 42nd-most-abundant element in the universe


    Coincidence? I think not!
    • Re:42 (Score:5, Funny)

      by Torodung (31985) on Wednesday March 26, 2008 @08:43PM (#22876482) Journal

      Its the ultimate answer to life and everything.

      According to wikipedia.

              Molybdenum is the 42nd-most-abundant element in the universe
      And it can hardly be coincidence that you fail to mention its atomic number is also 42!

      ZOMG! Is it April Fools' yet?

      --
      Toro
      • Re:42 (Score:4, Informative)

        by Silicon Jedi (878120) on Wednesday March 26, 2008 @08:46PM (#22876498)
        Holy crap! There are 42 protons in its nucleus!
        • Re: (Score:2, Informative)

          by rangek (16645)

          Holy crap! There are 42 protons in its nucleus!

          You dope. That is what the atomic number means.

        • by Thornburg (264444)
          Eegads. Who modded this "informative". It is a JOKE. The ENTIRE section of this thread relating to the number 42 is a joke. Please mod parent "funny" and mod the "that's what the atomic number means" post "didn't get the joke".
      • That's pretty much what makes it 42nd most abundant...
      • by AJWM (19027)
        And it can hardly be coincidence that you fail to mention its atomic number is also 42!

        Not only that, but when you multiply six by nine (in base ten), you get 54 -- which is the average number of neutrons in a molybdenum nucleus. (Is there anyone here that does not know that 6x9=42 in base 13?)

        Hmm...
  • by Anonymous Coward
    The universe used to be full of life, it's really quite a common occurrence, but for some reason the Earth, and other distant planets on the edges of galaxies, were mined for molybdenum, causing us to be the last lifeforms ever produced by a fertile cosmos. This teeming universe of life is long gone, for various reasons, but because these were chosen backwaters for exploitation, these final planets of life are completely unable to communicate or realize that reality. The distance is simply too great to span
    • by CRCulver (715279)
      Larry Niven's World of Ptaavs, now one of his most forgotten novels but important as his first Known Space book, had the Earth being a "food planet" of galactic empire several billion years ago. Humanity ended up evolving out of the ooze that was being grown for food.
      • by great om (18682)
        how does that explain the Pak?
        • Re: (Score:1, Informative)

          by Anonymous Coward
          Presumably Niven didn't anticipate the Pak when writing World of Ptaavs. But there's not really any need to retcon. Characters in World of Ptaavs assumed that humanity evolved from Slaver food species on Earth. They were just slightly wrong. Food species on Earth did become highly evolved, but never became intelligent. The Pak evolved from the same sort of food species growing on a distant planet. A Pak colony was sent to Earth and somehow became lost, and then Homo sapiens evolved from the remnant
        • by AJWM (19027)
          It doesn't. Grandparent misspoke, he should have said that all(?) Earth life except primates evolved from Thrint foodyeast. Primates evolved from the survivors of a failed Pak colonization attempt.

          Of course it's entirely possible that Pak evolved from foodyeast too, in which case the GP is correct.
        • by Evil Pete (73279)

          Ahhh. World of Ptavvs. Earth was a food world of the Slavers [wikipedia.org]. Creatures which could telepathically dominate any species. The Tnuctip [wikipedia.org], clever little buggers, fomented a revolution with the Bandersnatchi (who were immune to the Slavers telepathy, by design) against the Slavers. Who promptly, with great spite, wiped out all life in the galaxy. The Bandersnatchi on Earth presumably died out. Leaving the algae to evolve.

          Protectors don't even come into it. Though Slavers are mentioned in Protector, Roy Truesdal

      • by sssssss27 (1117705) on Wednesday March 26, 2008 @09:30PM (#22876854)
        That reminds me of a quote from Chuck Palahniuk:

        "Centuries ago, sailors on long voyages used to leave a pair of pigs on every deserted island. Or they'd leave a pair of goats. Either way, on any future visit, the island would be a source of meat. These islands, they were pristine. These were home to breeds of birds with no natural predators. Breeds of birds that lived nowhere else on earth. The plants there, without enemies they evolved without thorns or poisons. Without predators and enemies, these islands, they were paradise. The sailors, the next time they visited these islands, the only things still there would be herds of goats or pigs. .... Does this remind you of anything? Maybe the ol' Adam and Eve story? .... You ever wonder when God's coming back with a lot of barbecue sauce?"
        • by maxume (22995)
          He likes Lea & Perrins.
        • by Torodung (31985)

          Does this remind you of anything? Maybe the ol' Adam and Eve story? .... You ever wonder when God's coming back with a lot of barbecue sauce?"

          Do you wonder what the Lake of Fire is? Did you know that the original title of the Bible is "Preparing Humans?" Can you picture the classical image of "Satan" dressed up like Col. Sanders?

          I mean, did you ever wonder why it seems so easy to go to hell? To prepare us to accept our fate. It's all there to condition us to behave like Douglas Adams' Arcturan Megacow!

          Thanks for the hilarious post.

          --
          Toro

          • by Forbman (794277)
            No, no, no... "To Serve Man". That's the title...

            One of my favorite Twilight Zone episodes.
  • to build Crow T. Robot.
  • by frovingslosh (582462) on Wednesday March 26, 2008 @09:02PM (#22876646)
    Bacteria cannot fix nitrogen efficiently when they are deprived of molybdenum So when God created the earth, all of his nitrogen was broken?
    • Bacteria cannot fix nitrogen efficiently when they are deprived of molybdenum So when God created the earth, all of his nitrogen was broken?
      If "broken" means N2 and "fixed" means amines [wikipedia.org], then God must have had a nitrogen fixation [wikipedia.org].
      • I have lost faith in /. Have we fallen so far that we have stopped modding up jokes which require a degree to understand, i thought that was one of the founding principles of this site.
    • by pangu (322010)

      So when God created the earth, all of his nitrogen was broken?
      --
      Damn you Bill Gates!(TM)
      Bill Gates is not God.
  • by TrebleJunkie (208060) <ezahurakNO@SPAMatlanticbb.net> on Wednesday March 26, 2008 @10:11PM (#22877202) Homepage Journal
    Damn near killed 'um!!

    *ducks*
  • Imagine a world without zinc, er, molybdenum!

              Brett
  • I find the assumption that the only way of fixing nitrogen requires molybdenum rather implausible. Chances are that molybdenum got used for that purpose once it became available, and before that, nitrogen fixation was either not needed (because there was enough ammonia and/or nitrous oxide around), or there were other pathways.
    • by ceoyoyo (59147)
      The article says "fix molybdenum efficiently."

      Just like life as we know it doesn't technically need oxygen, but oxygen dependent metabolism is SO much more efficient that when it comes along it not only blows everything else away but also opens up a lot of new possibilities for life.
  • Given that we're exploring alternative histories here, wouldn't it be more accurate to say that if molybdenum had been more abundant, animal life might have evolved sooner? The normal state is after all what we're looking at.

    This discovery could be useful for accelerating the terraforming of planets, eventually.
  • Excuse my sheer ignorance of the subject, but may I ask what humans, plants and pachyderms have in common to lump us into the same group that other creatures aren't lumped in to?

    Is there any reason we're being lumped along with things like elephants and trees or was that list just a very small sample of the creatures included such that the term covers pretty much all living creatures? Presumably creatures like primates are also in this group?
    • Re: (Score:2, Informative)

      by Blastercorps (762119)
      Compared to prokaryotes [wikipedia.org] (simple life, bacteria), all eukaryote life [wikipedia.org] (advanced life like plants pachyderms and people) are essentially cousins. This is a split that happened at the dawn of life on earth. This article theorizes that the split would have happened earlier if not for a lack of molybdenum and the resultant lack of usable nitrogen.
  • by uberhobo_one (1034544) on Thursday March 27, 2008 @09:55AM (#22881170)
    It's so sad when bad things happen to good ideas. The fact that there may have been dearth of molybdenum in the early oceans isn't a crippling blow to the development of eukaryotes.

    Nitrogenase, the enzyme that performs nitrogen fixation today, commonly uses, but doesn't require, molybdenum for its function. There are forms of the enzyme that use vanadium or iron as a cofactor to the ubiquitous iron-sulfur cluster that actually performs the chemistry.

    I don't know if this event happened before or after the iron catastrophe, but the fact that the enzyme uses iron anyway makes me believe that there must have been enough iron around the oceans back then. Methinks the author's running off the old idea that the nitrogen reduction occurs on the molybdenum atom instead of one of the iron atoms in the iron-sulfur cluster.
  • I just knew there had to be an underlying scientific reason.
  • I work in a metallurgical research lab. We have lots of Molybdenum - but things seem pretty lifeless around here!

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