The breakup of Rodinia could have caused an increase in rainfall, because smaller continents with greater shoreline could be exposed to more rainfall. Rainfall, in turn, causes weathering of CO2 from land into the ocean, leading to decreased CO2 in the atmosphere. This could eventually result in ice forming at the poles, spreading slowly toward the equator. Ice reflects sunlight from the Earth's surface back into space, which would cool the Earth further, a phenomenon known as albedo. This positive feedback loop could result in complete or near-complete glaciation of the earth. Donnadieu et al. (2004) use climate models to test the hypothesis that the breakup of Rodinia could decrease the levels of atmospheric CO2 enough to initiate this process. They find that increased weathering resulting from changes in geography could have lowered Earth's average temperature by around 8 C, a level able to trigger a full glaciation.
In your comments, and for class on Thursday, think critically about this hypothesis. Do you think evidence is sufficient to support a Snowball Earth? What evidence is there against a Snowball Earth? What are your thoughts on using a modeling approach to study this problem? How would you study this problem? How do you think life could have survived during a Snowball Earth climate? How could the climate have escaped from a Snowball Earth glaciation? Most importantly, what questions do you have about the Snowball Earth hypothesis?
Citations:
Donnadieu, Yannick, Yves Godderis, Gilles Ramstein, Anne Nedelec, & Joseph Meert. 2004. A 'snowball Earth' climate triggered by continental break-up through changes in runoff. Nature 428: 303-306.
Hoffman, Paul F. & Daniel P. Schrag. 2000. Snowball Earth. Scientific American 282: 68-75.
I was wondering how much open or slushy water would have to be available for life to cling to existence on a snowball earth?
ReplyDeleteI was also wondering if there is very much evidence for life at the surface (i.e. not at the bottom of an iced over ocean near volcanoes) during all or any of the earth's snowball period and if so which period had the most surface life?
-Thanks
Jayda
Hi Jayda,
DeleteWe know from the similarity between microscopic algae found preserved in rocks at least a billion years old to extant (modern) forms of algae that there was continuity in life. However, this does not necessarily negate the idea of snowball earth. Microorganisms have been found in seafloor hotsprings (which would have continued during a snowball earth), extremely cold and dry climates such as Antarctica, and even in snow. However, keep in mind that this is an environment where there is very low carbon dioxide and the majority of carbon dioxide would be found in the ocean because it would be produced by volcanic activity. Since the algae and bacteria found in the seawater would need carbon to survive, chances are they would be more likely to be found in seawater. Furthermore, if there was sufficient carbon dioxide to survive on surface, chances of finding evidence of living lifeforms would be slim since carbonate rocks are formed by underwater volcanic activity, which records the proportion of 13C to 12C, indicating biological activity. Therefore, there would be no way, at least that I can think of, to determine biological activity at the surface.
Katie
Having little formal education in the various fields that Hoffman, Schrag and Danika are relying upon I find it difficult to imagine what force(s) would cause the break-up of Rodinia, and then the migration of the resultant pieces.
DeleteFurthermore, it is challenging to imagine Neoproterozoic life forms managing to survive repeated cataclysmic activities, such as adapting between extremes of cold and heat. Although, there are existing life forms near active volcanoes under the ocean, in hot springs, and on both poles. However, I have never heard of any research testing currently existing creatures ability to adapt over time to just one environmental change ie. temperature, much less other chemical events one would expect to find in water during cataclysmic activity.
What is less taxing to imagine, given my limited knowledge base, is accepting a geological finding as a tangible ground to forming a hypotheses. Hoffman and Schrag found caps, which are apparently found globally supporting their findings of global glaciation.
Perhaps a holistic view of these various hypotheses would find there's some truth in each of them.
I appreciate the use of modelling to check the feasibility of a theory, however, I disagree that computer modelling should be used as proof positive for a scientific claim. What is possible in modelling is not always probable in the real world.
ReplyDeleteThe most interesting question to me is how life would survive in this case. The possibility of life surrounding volcanic vents and in the deeper unfrozen trenches of the ocean is the obvious conclusion. More interesting was recent research I read (looking for citations) that indicated scientists had revived bacteria that had been frozen in ice for several million years, this opens the possiblity that not only would bacteria live near heat sources, but could also simply wait out the snowball earth affect while frozen in glaciers.
Edit: This is Connor Lemp, blogspot isn't playing nice with my google account, and refuses to change my name to anything except "Unknown".
DeleteAlso, Citations!
http://www.newscientist.com/article/dn12752-microbes-can-survive-deep-freeze-for-100000-years.html
Hi Connor,
DeleteThis is a good point. Computer modelling should never be used as proof positive for a scientific claim (in fact, no one test in itself should ever be used as "proof positive"). However, keep in mind computer modelling can certainly be useful in investigating the probability of certain scenarios.
I agree, it is amazing the harsh environments that life can inhabit. That sounds like a really cool article, and I think that is an excellent point. Thanks for posting the link to the article!
In fact, anytime someone finds a neat article related to the subject matter, please be sure to share it with the group!
This experiment did a good job of showing that a snowball Earth was possible under the conditions that were probably present at the time of the break up of Rodinia. The experiment was very specific in its required conditions. It showed that increased coastal area and run offs alone were not enough to bring CO2 levels low enough for a snowball earth. Weathering of basaltic provinces was also necessary, which only occurred when those areas shifted away from the dry sub-tropics.
ReplyDeleteAs mentioned in the results, this specificity makes it hard to apply these results to the other 2 or 3 snowball earths that are thought to have occurred.
Though, on the other hand, the specificity of the experiment shows the importance of taking into account many different variables working together in order to lower the temperatures enough.
This experiment seems to be the introduction to further research into the creation snowball earths, showing that they are possible, but not yet showing proof that it has happened.
You make an interesting point - the breakup of Rodinia happened only once, so how did we get three snowball earths?
DeleteHi. Metta RavenHeart here. The Snowball Earth hypothesis is intriguing but narrow in its scope. The assumption that the earth was covered by ice because of glacial evidence on all continents, many of which were in tropical regions, is a leap of logic. One supporting argument that the entire ocean was covered by ice and this explains the massive extinction, seems to be unsupportable. I too agree that modeling is a step forward in moving from theory to plausible answers, but it is not proof positive. The continuum of life is far too complex to be modeled. Perhaps the Snowball Earth Hypothesis is too static. Many more options could have been at work during this glaciation and warming, such as methane releases, etc. It will be fun to discuss
ReplyDeleteMetta, I agree that life and earth processes are complex and that models do not capture all the variability and possibilities. However, models do play an important role anyway, even if scientists know that models have limitations. Why do you think they may be useful despite their limitations?
DeleteJust a quick concern: I just saw in the syllabus that our blog posting is to be completed by 8pm. Can we as a class convince you to extend that a few hours. I do 12 hour days 5 days a week and dont get home or have any time to work until 7 or 8 pm.
ReplyDeleteI dont agree with most of the class postings. I think this is a great paper, well supported and not at all a leap of logic or narrow in its scope. I was a little unclear about a few items after reading the article, but then again I am not a climatologist or a geo-anything. Most of my questions and concerns were addressed in the follow up paper by Hoffman and Schrag. I'm a little confused why or how the idea of Earth being covered in ice/snow and therefore leading to mass extinction could be considered unsupportable? If there is proof/evidence that glaciers were once in all continents and at all latitudes in the same time period, wouldn't it follow logically that there would be mass extinction?
My first thought was are all the deposits the same age and if not then what is the variance in the age. So if i am wondering, then . . . . I would have to agree with Danika that the climate model simulation in the experiment did show the "possibility" of a Snowball Earth being plausible, however there still was no conclusive evidence and there are other variables that need to be taken in to account such as plate tectonics.
ReplyDeleteAs for could life survived i believe that Hoffman and Schrag are correct that elaborate mechanisms 'genetic alteration' in organisms would cause them to adapt - the will to survive.
Having little formal education in the various fields that Hoffman, Schrag and Danika are relying upon I find it difficult to imagine what force(s) would cause the break-up of Rodinia, and then the migration of the resultant pieces.
ReplyDeleteFurthermore, it is challenging to imagine Neoproterozoic life forms managing to survive repeated cataclysmic activities, such as adapting between extremes of cold and heat. Although, there are existing life forms near active volcanoes under the ocean, in hot springs, and on both poles. However, I have never heard of any research testing currently existing creatures ability to adapt over time to just one environmental change ie. temperature, much less other chemical events one would expect to find in water during cataclysmic activity.
What is less taxing to imagine, given my limited knowledge base, is accepting a geological finding as a tangible ground to forming a hypotheses. Hoffman and Schrag found caps, which are apparently found globally supporting their findings of global glaciation.
Perhaps a holistic view of these various hypotheses would find there's some truth in each of them.
Great article overall. I haven't read many model-based papers, especially about unfamiliar topics such as this, but I thought it was a great intro to the topic. I also thought it highlighted the utility of using complex models to parse underlying mechanisms of a process - what a powerful tool! As discussed, the techniques used may not shed light on other instances of snowball earth, but at least for the Sturtian event in question, it is clear that geography-induced weathering is a plausible explanation to drive such low CO2 as necessary to initiate this particular snowball.
ReplyDelete