CYANOBACTERIA BLOOM: Thanks to algal blooms like this one, the Earth's atmosphere is 21 percent oxygen.
Image: Courtesy of J.L. Graham / USGS
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It's hard to keep oxygen molecules around, despite the fact that it's the third-most abundant element in the universe, forged in the superhot, superdense core of stars. That's because oxygen wants to react; it can form compounds with nearly every other element on the periodic table. So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff?
The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. In fact, all the plants on Earth incorporate symbiotic cyanobacteria (known as chloroplasts) to do their photosynthesis for them down to this day.
For some untold eons prior to the evolution of these cyanobacteria, during the Archean eon, more primitive microbes lived the real old-fashioned way: anaerobically. These ancient organisms—and their "extremophile" descendants today—thrived in the absence of oxygen, relying on sulfate for their energy needs.
But roughly 2.45 billion years ago, the isotopic ratio of sulfur transformed, indicating that for the first time oxygen was becoming a significant component of Earth's atmosphere, according to a 2000 paper in Science. At roughly the same time (and for eons thereafter), oxidized iron began to appear in ancient soils and bands of iron were deposited on the seafloor, a product of reactions with oxygen in the seawater.
"What it looks like is that oxygen was first produced somewhere around 2.7 billion to 2.8 billon years ago. It took up residence in atmosphere around 2.45 billion years ago," says geochemist Dick Holland, a visiting scholar at the University of Pennsylvania. "It looks as if there's a significant time interval between the appearance of oxygen-producing organisms and the actual oxygenation of the atmosphere."
So a date and a culprit can be fixed for what scientists refer to as the Great Oxidation Event, but mysteries remain. What occurred 2.45 billion years ago that enabled cyanobacteria to take over? What were oxygen levels at that time? Why did it take another one billion years—dubbed the "boring billion" by scientists—for oxygen levels to rise high enough to enable the evolution of animals?
Most important, how did the amount of atmospheric oxygen reach its present level? "It's not that easy why it should balance at 21 percent rather than 10 or 40 percent," notes geoscientist James Kasting of Pennsylvania State University. "We don't understand the modern oxygen control system that well."
Climate, volcanism, plate tectonics all played a key role in regulating the oxygen level during various time periods. Yet no one has come up with a rock-solid test to determine the precise oxygen content of the atmosphere at any given time from the geologic record. But one thing is clear—the origins of oxygen in Earth's atmosphere derive from one thing: life.
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22 Comments
Add CommentI can't believe there are no comments? Maybe people are shocked to think that evolution might just be happening for real!
Reply | Report Abuse | Link to thisI can't believe there are no comments? Maybe people are shocked to think that evolution might just be happening for real!
Reply | Report Abuse | Link to thisA possible reason for no comments is this article doesn't say anything new and while it poses several good questions, gives no inkling at all, nor resources, toward possible answers.
Reply | Report Abuse | Link to thisIt might have mentioned that the reason we could have evolved to be the oxygen breathing creatures that we are today is eukaryotes formed symbiotic relationships with oxygen metabolizing bacteria that eventually became mitochondria. This relationship might explain the ambivalent relationship we have with oxygen: we need it for energy but 'oxidative stress' is very destructive to all our systems.
This article might have mentioned Lynn Margulis' seminal work, "Early Life," or Christian de Duve's excellent and very readable book "Vital Dust," or the fine collection of papers by the original researchers, written for lay audiences, edited by William Schopf, "Life's Origin: The Beginnings of Biological Evolution"
BTW, the sub-heading of this article, "the details are lost in geologic time' is, let's say, equivocal.
Reply | Report Abuse | Link to thisThis article cites Harvard/UPenn geochemist H.D. Holland. His 1999 paper (3 pages) is available for free on the web (http://www.atmos.washington.edu/~davidc/ASTBIO502/Holland99.pdf) His 2009 longer paper published in ScienceDirect costs $31.
In big cities the oxygen content is as low as 15%, so it shows that human activity can actually alter this oxygen control system. Negatively . We, through combustion of fossilfuels and lack of plant in cities, consume oxygen and spew out CO2 (2 oxygen binded with one carbon ) in our industrial world. So not only do we increase CO2levels but we decrease O(xygen) levels. You cannot increase CO2 without decreasing oxygen levels. It goes hand in hand. When you create a new CO2 molecule you have waste 2 O(oxygen) molecules.
Reply | Report Abuse | Link to thisSo if evolution or God created a 21% oxygen control system on earth, we humans are now greater, in a destructive way, than the creator of life on earth.
Of course we can increase CO2 levels AND oxygen. The CO2 humans are contributing are from fossil fuels and are only now being re-introduced into the atmosphere. Let us not forget that every molecule of CO2 results in an O2 molecule via photosynthesis. Hence, the more CO2 introduced, the more O2 in the atmosphere. In the end the %O2 should increase by burning more coal and oil.
Reply | Report Abuse | Link to thisThe article is not entirely correct.
Reply | Report Abuse | Link to thisCyanobacteria may not be responsible for the oxygen in the atmosphere.
Cyanobacteria evolved about 3500 million years ago, they were the first phytoplankton and at that point in time there was virtually no oxygen in the atmosphere.
By 1500 million years ago, the oxygen level of the atmosphere increased to only < 1 %.
Indicating that Cyanobacteria DO NOT add much oxygen to the atmosphere.
Other phytoplankton like Green Algae evolved about 1500 million years ago and only then the oxygen level started to increase.
Diatom Algae contribute more oxygen than all other phytoplankton / algae.
Atmosphere was created on the second day and plants were created on the third. So, there is a bit of a problem with the explanation in this article. And yes, I know there will be some that say, "There is no God" however, we could also say, "The earth is flat" and, "The sun revolves around the earth" among other things that were proven to be untrue. There is more proof to the existence of God and the validity of the Bible than there is for this article.
Reply | Report Abuse | Link to thisRhodatbs.Please Try to make sense. The 6 day creation theory is foolish beyond belief. It is so stupid a child could not even accept it. Grow up
Reply | Report Abuse | Link to thisIt is more then 50 years ago, but then I learned at the university that Oxygen was produced by the very early
Reply | Report Abuse | Link to thisplant systems to defend their place in the earth where they grows. Whoever has a garden knows that some plants
do not like each other.Interesting comments !
Dr.Kamlander@aon.at
The oxygen we breathe was vilified by many pre-oxygen organisms, who strived to limit its manufacture.
Reply | Report Abuse | Link to thisFortunately for us, they failed in their attempt to limit the self-destructiveness of the anaerobic organisms producing today's wonderful abundance of oxygen.
Hooray for those who opposed those stupid anti-oxygen crusaders.
You are an idiot. Many God-Fearing people believe in Evolution. They simply hesitate to speak its name - one of the many names of Satan.
Reply | Report Abuse | Link to thisHail Satan!
Evolution proclaims its allegiance to you, as one tool which extinguishes God's ignorance. Hail! Hail Satan!
Evolution and particle physics threatens your dominion over our souls. So does Geology and Astronomy. smite the knowledge seekers, Oh God. Smite them, so we ignorance farmers can reap what we sow.
Oxygen - a Pollutant of Ages, smiter of subsequent Life.
Reply | Report Abuse | Link to thisI do wish that early microbes established their own EPA, in order to keep oxygen under control. That way, we'd all be cyanobacteria, Pure Forms, unsullied by Oxygen....
Prior life is what I meant, rather than subsequent - I'm drunk, what do you expect....
Reply | Report Abuse | Link to thisI have a question, if oxygen's origin in the atmosphere is through photosynthesis, which requiers water. Water consists out of one hydrogen atom and 2 oxygens, then is it possible to say that through vaporization of water by the son or by some other factor, oxygen reached the atmosphere before it reached the atmosphere by photosynthesis? I know that seperating oxygen from hydrogen takes emencely high tempertures, however i believe that in Earth's early stages tempertures were quite high...
Reply | Report Abuse | Link to thisAny response would be appreciated.
Water is not one part hydrogen and two parts oxygen, but the other way around.
Reply | Report Abuse | Link to thisH2O
2 parts hydrogen, 1 part oxygen.
Vaporization of water only breaks the ionic bonds of hydrogen.
I'm not sure if conditions of the early earth were hot enough to break the covalent bonds of hydrogen and oxygen. I seriously doubt it, though.
How could you argue, after reading this article, that people are afraid to comment "because evolution might just be happening for real?" If you knew the basics of atmospheric physics you would know that without ozone there can be no life because of the ultra violent rays from the sun. With that being said, ozone, nevertheless, is ONLY credited from life - algae, etc. So if you can not have life without ozone - or ozone without life, which came first in the evolutionary process?...Actually this is little more than scientific proof for special creation...
Reply | Report Abuse | Link to thisClimate change skeptics deny humans could possibly be so powerful as to have an impact on the climate, yet our oxygenated atmosphere is here totally due to blue-green algae. Does that mean bacteria are more powerful than humans, or that maybe skeptics need to rethink how much impact a creature can have on its environment?
Reply | Report Abuse | Link to thisI am somehow not convinced that biotic factors are solely responsible for creating 21% of atmosphere (around 40 million moles of oxygen). I am not sure what is the photosynthetic oxygen production rate per gram biomass of cyanobacteria but it seems unlikely that its the sole catalyst for oxygenesis.
Reply | Report Abuse | Link to thisThere may be additional issues here. Since cyanobacteria produced oxygen, it should have developed antioxidant machineries. By the time cyanobacteria flourished, some dependent heterotrophs must have evolved and they also would need antioxidants, as they are expected to thrive in close proximity to the autotrophs. There is a likelihood that aerobic respiration co-evolved with biotic oxygenesis. This would have further delayed the build up of oxygen in the atmosphere.
Basically, we need to know how much of cyanobacteria is required to produce this much of oxygen.
"Vaporization of water only breaks the ionic bonds of hydrogen"
Reply | Report Abuse | Link to thisthere are no ionic bonds in water.. heating breaks the physical bonds such as hydrogen bonds and van-der waals attractive forces.. if high enough, heat can cause breakage of covalent bonds (for e.g. in explosives). But water is too stable for that. In photosynthesis there is a photochemical lysis of water catalysed by chlorophylls.
I think it's important to observe the world with gawp mouthed humility. Overpopulation and Global Climate Change theories are practical and justified, but they are theories. Threaded through both are some moments of hubris. Objectively there are a couple of things that make me wonder, how long have we observed and recorded global temperatures and population counts reliably? Can we make statements about Nature that are romantic when really it is our butts that are headed to an extinction event? I mean, perhaps it is our Nature to be the nail in the coffin for our mammalian age--so to speak. And since God made the world and the world is round and cycles around the sun, couldn't we suppose God counts time in a much more godly way? Like on an omni-versal Timex? And when He hears us arguing about how many "days" it took to create this or that He can't help but chuckle like we're little children arguing over who has the bigger slice of pie?
Reply | Report Abuse | Link to thisWhat IS the temperature that water breaks down? Also, considering all the variables that could have been at work--could super cell electric storms have decomposed H20 as they cycled over the seas, using electrolysis? We have, as a species, evolved in a relative period of environmental calm but even so we can see that weather is a massive game changer. The Earth may have had all sorts of tools that our atmosphere owes itself to, cyanobacteria could have been some sort of compounding factor maybe?
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