“Great Oxidation Event” –A New Discovery of Evolutionary Singularity that Transformed the Planet

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For most terrestrial life on Earth, oxygen is necessary for survival. But the planet's atmosphere did not always contain this life-sustaining substance, and one of science's greatest mysteries is how and when oxygenic photosynthesis—the process responsible for producing oxygen on Earth through the splitting of water molecules—first began. Now, a team led by geobiologists at the California Institute of Technology (Caltech) has found evidence of a precursor photosystem involving manganese that predates cyanobacteria, the first group of organisms to release oxygen into the environment via photosynthesis.


"Oxygen is the backdrop on which this story is playing out on, but really, this is a tale of the evolution of this very intense metabolism that happened once—an evolutionary singularity that transformed the planet," says Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor of the study. "We've provided insight into how the evolution of one of these remarkable molecular machines led up to the oxidation of our planet's atmosphere, and now we're going to follow up on all angles of our findings."

"Water-oxidizing or water-splitting photosynthesis was invented by cyanobacteria approximately 2.4 billion years ago and then borrowed by other groups of organisms thereafter," explains Fischer. "Algae borrowed this photosynthetic system from cyanobacteria, and plants are just a group of algae that took photosynthesis on land, so we think with this finding we're looking at the inception of the molecular machinery that would give rise to oxygen."

The findings, outlined in the June 24 early edition of the Proceedings of the National Academy of Sciences (PNAS), strongly support the idea that manganese oxidation—which, despite the name, is a chemical reaction that does not have to involve oxygen—provided an evolutionary stepping-stone for the development of water-oxidizing photosynthesis in cyanobacteria.

Written By: The Daily Galaxy
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  1. Manganese is soluble in seawater. Indeed, if there are no strong oxidants around to accept electrons from the manganese, it will remain aqueous, Fischer explains, but the second it is oxidized, or loses electrons, manganese precipitates, forming a solid that can become concentrated within seafloor sediments.

    The seafloor geochemistry has opened up much new evidence.

    In addition to the manganese deposits, there are huge iron ore deposits from the gradual removal of dissolved iron from prehistoric seas, as reducing elements and molecules, persistently stripped oxygen from the atmosphere and seawater : – before oxygen-photosynthesis finally caused an extinction of anaerobic organisms which were unable to adapt to oxygen respiration in exposed habitats.

    Evidence for a Persistently Iron-rich Ocean Changes Views on Earth’s Early Historyhttp://newsroom.ucr.edu/2709 – Discovery challenges previous models for the environment in which early life evolved

    RIVERSIDE, Calif. – Over the last half a billion years, the ocean has mostly been full of oxygen and teeming with animal life. But earlier, before animals had evolved, oxygen was harder to come by. Now a new study led by researchers at the University of California, Riverside reveals that the ancient deep ocean was not only devoid of oxygen but also rich in iron, a key biological nutrient, for nearly a billion years longer than previously thought —right through a key evolutionary interval that culminated in the first rise of animals.

    “The implications of our work are far reaching,” said Timothy Lyons, a professor of biogeochemistry and the principal investigator of the study. “We will need to rethink, in a fundamental way, all of our models for how life-essential nutrients were distributed in the ocean through time and space.”

    Study results appear in the Sept. 8 issue of Nature.

    Previous ocean chemistry models

    Most scientists agree that the early Earth, before 2.4 billion years ago, contained only trace quantities of oxygen and that the oceans were dominantly full of dissolved iron. But there is far less agreement among scientists about the chemical composition of the ocean during the middle chapters of Earth’s history in the wake of atmospheric oxygenation—about 2.4 to 0.5 billion years ago—when the diversity of organisms that we know today, including the animals, first got their footing.

    Classic models for this time window maintain that the ocean, all depths, became rich in oxygen in parallel with its first accumulation in the atmosphere. This increase in oxygen in seawater has been linked to the disappearance of iron ore deposits known as ‘banded iron formations,’ the source of almost all of the iron used to make steel today. Oxygen, the argument goes, would have ‘rusted’ the oceans, stripping them of dissolved iron.

    More than a decade ago, however, another idea gained traction: hydrogen sulfide. Produced by bacteria in the absence of oxygen, hydrogen sulfide, it was argued, might instead have scrubbed the iron out of the ocean during Earth’s middle history, dealing the fatal blow to the iron deposits. In an ocean full of hydrogen sulfide, diverse life-sustaining elements, including iron, can be stripped from the seawater, potentially causing a biotic crisis.

    Fresh perspective

    “The problem all along was a general lack of physical evidence in the oceans for the amounts of oxygen, iron, and sulfide in the Earth’s middle history, particularly in a critical billion-year window between roughly 1.8 and 0.8 billion years ago,” said Noah Planavsky, a doctoral student in UC Riverside’s Department of Earth Sciences and the lead author of the new study. “Some earlier work supported a return to an iron-rich ocean 0.8 billion years ago. Rather than a return, however, we predicted that iron may have dominated the deep ocean continuously right up to the oxygenation and concomitant rise of animals a mere half-billion years ago.”

    Planavsky and his colleagues at UCR and in Canada, Australia, and China sought to remedy the data deficiency. New rock samples they collected from across the globe suggest a previously unknown continuity in ocean chemistry over much of its history. These data, the first of their kind, point towards continuous oxygen-poor, iron-rich conditions for 90 percent of Earth’s history, with oxygen and hydrogen sulfide, when present, limited mostly to the surface layers and along the margins of the oceans, respectively.

    The task now is to reconsider whether the purported shortages of nutrients attributed to widespread hydrogen sulfide were indeed real and a throttle on early evolution. “Our new knowledge that the deep ocean was anoxic and iron-rich does not mean life had it easy, though,” Lyons says. “Enough sulfide could have persisted around the edges of the ocean to severely limit other key nutrients. We are still testing this hypothesis.”

    Ironing out the details

    The researchers’ results also indicate that neither oxygen nor hydrogen sulfide turned off iron deposition around 1.8 billion years ago, when the last major iron ores were seen. They suggest instead that hydrothermal systems on the seafloor are the most important factor controlling the distribution of iron ore.

    “These hydrothermal systems are high-temperature vents on the seafloor tied to magmatic activity, and they can pump huge amounts of iron into the ocean,” Planavsky explained. “Previous researchers have suggested that there was a decrease in the amount of iron from hydrothermal systems around 1.8 billion years ago. Our results support this idea with compelling physical evidence, while showing that iron could persist in the ocean at levels below those necessary to form ore deposits.”

    “The next step is to better merge this refined chemical perspective with traditional and emerging views of evolving life, recognizing that life and the environment co-evolve in an intimate dance of cause-and-effect relationships,” Lyons added.

    This is suggesting stratification of early oceans with varying chemistries at different levels.

  2. In discussions of early Earth, it is important to consider it in the context of interaction with the rest of the Solar-System along the time-line of events.

    This link has various instructive diagrams to illustrate points. I think it covers modern scientific thinking of a very extensive topic quite concisely.

    http://astroclock2010.wordpress.com/cosmic-timeline-17/

    The currently accepted method by which the planets formed is known as accretion, in which the planets began as dust grains in orbit around the central protostar.

    The inner Solar System was too warm for water and methane to condense, so the planetesimals, as the forming planets are called, could only form from compounds with high melting points, such as metals like iron, nickel, and aluminium and rocky silicates. These rocky bodies would become the terrestrial planets, Mercury, Venus, Earth, and Mars. These compounds are quite rare in the universe, so the terrestrial planets could not grow very large. These forming planets grew to about 0.05 Earth masses and ceased accumulating matter about 100,000 years after the formation of the Sun. It was the period involving subsequent collisions and mergers between these planet-sized bodies that allowed these terrestrial planets to grow to their present sizes. When the terrestrial planets were forming, they remained immersed in a disk of gas and dust.

    At the end of the planetary formation epoch the inner Solar System was populated by 50–100 Moon- to Mars-sized planetary objects.

    Further growth was possible only because these bodies collided and merged in a period which took less than 100 million years. These objects would have gravitationally interacted with one another, tugging at each other’s orbits until they collided, growing larger until the four terrestrial planets we know today took shape. One such giant collision is believed to have formed the Moon, while another removed the outer envelope of the young Mercury.

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    The gas giant planets, Jupiter, Saturn, Uranus, and Neptune formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where the material is cool enough for volatile icy compounds to remain solid.

    The ices that formed the Jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the Jovian planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements. Planetesimals beyond the frost line accumulated up to four Earth masses within about 3 million years. Today, the four gas giants comprise just under 99% of all the mass orbiting the Sun.

    Theorists believe it is no accident that Jupiter lies just beyond the frost line. Because the frost line accumulated large amounts of water via evaporation from infalling icy material, it created a region of lower pressure that increased the speed of orbiting dust particles and halted their motion toward the Sun.

    In effect, the frost line acted as a barrier that caused material to accumulate rapidly at this distance from the Sun. This excess material coalesced into a body of about 10 Earth masses, which then began to grow rapidly by swallowing hydrogen from the surrounding disc, reaching 150 Earth masses in only another 1000 years and finally topping out at 318 Earth masses.

    Saturn may owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume.

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    Asteroid belt
    The outer edge of the terrestrial region is called the asteroid belt. The asteroid belt initially contained more than enough matter to form 2–3 Earth-like planets, and, indeed, a large number of planetesimals formed there. As with the terrestrials, planetesimals in this region later coalesced and formed 20–30 Moon- to Mars-sized planetary embryos, however, the proximity of Jupiter meant that after this planet formed, 3 million years after the Sun, the region’s history changed dramatically.

    Orbital resonances
    An orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, and these gravitational influences of both Jupiter and Saturn are particularly strong in the asteroid belt. These gravitational interactions with more the more massive forming planetary material scattered many planetesimals into those resonances. Jupiter’s gravity increased the velocity of objects within these resonances, causing them to shatter upon collision with other bodies, breaking up into smaller objects rather than combining to make larger objects.

    As Jupiter migrated inward, following its formation, resonances would have swept across the asteroid belt. The effects of the giant planets left the asteroid belt with a total mass equivalent to less than 1% that of the Earth, composed mainly of small planetesimals.

    A second period that brought the asteroid belt down close to its present mass is believed to have followed when Jupiter and Saturn entered a temporary 2:1 orbital resonance. The inner Solar System’s period of giant impacts probably played a role in the Earth acquiring its current water content from the early asteroid belt. Water is too volatile to have been present at Earth’s formation and must have been subsequently delivered from outer, colder parts of the Solar System. The water was probably delivered by small planetesimals thrown out of the asteroid belt by Jupiter.

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    Planetary movements of the outer planets
    According to a theory called the nebular hypothesis, the outer two planets are in the “wrong place”. The ice giants Uranus and Neptune exist in a region where there was hardly any material of the solar nebula from which they could form and their longer orbital times also suggests that their formation in this part of the solar system where we see them now does not make sense. An explanation could be that the two ice giants formed in orbits near Jupiter and Saturn, where more material was available, but then moved outward to their current positions over hundreds of millions of years.

    After the formation of the Solar System, the orbits of all the giant planets continued to change slowly, influenced by their interaction with large number of remaining planetesimals. After 500–600 million years (about 4 billion years ago) Jupiter and Saturn fell into a 2:1 resonance; Saturn orbited the Sun once for every two Jupiter orbits. This resonance created a gravitational push against the outer planets, causing Neptune to surge past Uranus and plough into the ancient Kuiper belt.

    The planets scattered the majority of the small icy bodies inwards, while themselves moving outwards. These planetesimals then scattered off the next planet they encountered in a similar manner, moving the planets’ orbits outwards while they moved inwards. This process continued until the planetesimals interacted with Jupiter, whose immense gravity sent them into highly elliptical orbits or even ejected them outright from the Solar System. This caused Jupiter to move slightly inward. Those objects scattered by Jupiter into highly elliptical orbits formed the Oort cloud; those objects scattered to a lesser degree by the changing orbit of Neptune formed the current Kuiper belt and scattered disc.

    Models of this indicate that part of this inward deflection was the Late heavy bombardment of Earth and the inner Solar-system.

    This explains the Kuiper belt’s and scattered disc’s present low mass. Some of the scattered objects, including Pluto, became gravitationally tied to Neptune’s orbit, forcing them into mean-motion resonances. Eventually, friction within the planetesimal disc made the orbits of Uranus and Neptune circular again.

    The precise origins of the Kuiper belt and its complex structure are still unclear, and astronomers are awaiting the completion of several wide-field survey telescopes such as Pan-STARRS and the future LSST, which should reveal many currently unknown KBOs. These surveys will provide data that will help determine answers to these questions.

    The Kuiper belt is believed to consist of planetesimals; fragments from the original protoplanetary disc around the Sun that failed to fully coalesce into planets and instead formed into smaller bodies, the largest less than 3,000 km (1,864 mi) in diameter.

    Stable orbits of the inner planets
    In contrast to the outer planets, the inner planets are not believed to have migrated significantly over the age of the Solar System, because their orbits have remained stable following the period of giant impacts.

    It is important to bear in mind that after its initial cataclysmic formation, the Earth throughout its evolution, has been acquiring many tonnes material from space, while losing some light elements from its upper atmosphere, – as it is still doing today.

    In its early history it suffered bombardments and collisions, in the process of its formation as a rocky planet, and then later bombardments of material from the outer Solar-System, – as the gas giants rearranged themselves, (around 4 billion years ago) due to gravity, impact drag, orbital resonances, and conservation of angular momentum.

    • In reply to #2 by Alan4discussion:
      (Whoops – this is meant to be on the Evolution thread…)

      “It is dishonest or ignorant to… imply that the models… can be dismissed on spurious grounds and pseudo-problems. I had noted that in the similar doubt-mongering about the bombardment of rocky bodies with water-ice and organic molecules from the outer Solar-System, where the superficial reading of words like ‘speculative’ and ‘controversial’ – (applied to specific models), is misrepresented as applying to the topic generally – in support of the process of incredulity.”

      The undeniable controversy about models is within NASA itself, with clearly opposing views, as already unambiguously quoted here as anyone can see if they bother to read it. The new accusation is that I used this to cast doubt on the whole LHB concept, “in support of of the process of incredulity.” But that is not so: your favourite WIkipedia makes this explicit. Here is yet another authoritative source:

      “So, did the Solar System go through what is known as the Late Heavy Bombardment (LHB)? Exciting new research, using data from the Lunar Reconnaissance Orbiter Camera (LROC) may cast some doubt on the popular LHB theory. It’s actually quite a heated debate, one that has polarized the science community for quite some time. In one camp are those that believe the Solar System experienced a cataclysm of large impacts about 3.8 billion years ago. In the other camp are those that think such impacts were spread more evenly over the time of the early Solar System from approximately 4.3 to 3.8 billion years ago.” http://www.astrobio.net/pressrelease/4435/new-research-casts-doubt-on-late-heavy-bombardment (based on Spudis, Wilhelms, and Robinson, 2011).

      Well, my source there is pretty authoritative, but I see you have tucked a source of your own elsewhere to bolster your claim:

      “Rather than have the scientific information buried in cascades of superficial incredulous verbosity, I have put it here [link] on this science thread.”

      Being scrupulous, I followed the link, and read cascades of peripheral stuff (almost 100 lines of it) with one short sentence about the LHB. As with my source, I took the liberty of examining yours to see the ultimate authority on which you base your abusive accusation of dishonesty and ignorance. Bear with me, because this is the best laugh I’ve had in some time. The text you quote at such inordinate length is from a blog entry based on a “project that took place in 18 primary and junior schools across the Borough of Basingstoke and Deane in the year 2000.” For any non-Brit reading this, those are schools for 4-11 year-olds.

      But that’s not the punchline. The sentence about the LHB isn’t in the source at all. No hint. You just inserted it in a source purporting to prove it. I can’t really put this any better than Monty Python:

      “I took the liberty of examining that parrot when I got it home, and I discovered the only reason that it had been sitting on its perch in the first place was that it had been NAILED there.”

      (BTW Still waiting for those credentials.)

    • In reply to #2 by Alan4discussion:

      In discussions of early Earth, it is important to consider it in the context of interaction with the rest of the Solar-System along the time-line of events.

      It is important to bear in mind that after its initial cataclysmic formation, the Earth throughout its evolution, has been acquiring many tonnes material from space, while losing some light elements from its upper atmosphere, – as it is still doing today.

      In terms of the oceans and atmosphere, material from the outer solar-System, has been involved in the chemical composition of Earth from early in its history.

      http://lunarscience.nasa.gov/articles/the-solar-systems-big-bang/

      What’s more, according to a leading theory now being explored in detail, that early era was capped by a truly cataclysmic event. About 3.9 billion years ago, the movement of the most massive planets dramatically rearranged the outer solar system. The shifting planets freed rocky and icy bodies from the solar system’s edge, commencing a bombardment of the entire retinue of planets.

      @2 – In its early history it suffered bombardments and collisions, in the process of its formation as a rocky planet, and then later bombardments of material from the outer Solar-System, – as the gas giants rearranged themselves, (around 4 billion years ago) due to gravity, impact drag, orbital resonances, and conservation of angular momentum.

      The later bombardments are described in the above NASA link.

  3. Moderators’ message

    In the interests of not having the same argument on two different threads, we have removed a comment by Logicophilosophicus that was also posted on the Evolution thread and has been responded to there.

    We know it can be difficult when similar issues crop up on more than one thread, but our Terms of Use prohibit posting the same comment on multiple threads.

    The mods

  4. In reply to the Moderator, post 4. How disappointing that you should have chosen to remove a post by logicophilosophicus. I, for one, enjoy reading articulate posts and I think you should reinstate this post for it’s articulate merits and as an example to others of the literary standard we might all aspire to on a website that describes itself as a ‘showcase’. Also, you might note for future reference, as I have done, that logicophilosophicus does not capitalise the username. Remember the example of history…one does not burn books!

  5. In reply to #6 by aroundtown:

    I wonder, purely a personal introspection, as to how the proposed hypothesis forwarded could affect the hypothesis for our moons creation.

    The Giant impact hypothesis of Earth-Moon formation pre-dates these late impact events and the anoxic evolution of Earth’s seas, by many millions of years.

    I wonder if remnants might remain on the moon that would further corroborate this proposition?

    Many impact craters on the Moon and other bodies, are dated to around 3.9 billion years ago when the outer giant planets were re-arranging the Solar System.

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