Friday, December 04, 2009

What is the Medea Hypothesis: Review Part Five

A Small Introduction

This is my latest post on the Medea Hypothesis as proposed by Dr Peter Ward of the University of Washington. The hypothesis is a counter to the more mainstream, if misused, Gaia Hypothesis. The Gaia Hypothesis states that the world is a self-regulating system with compensatory feedback systems to prevent or at least dampen, runaway effects. The primary instrument of the system in the Gaia Hypothesis is life and its interactions with the environment. The Medea Hypothesis is a rejection of that idea and in its place proposes that life does not, in fact, dampen the effects of runaway processes, but rather amplifies them. The short and perhaps overly dramatic version is that life is suicidal.

I have posted summarizing the Medea Hypothesis in several previous posts. You can find them here (introduction/competing theories of life), here (summary of what Medean Life), here (Paleo Medean Events) and here (biodiversity through time). The complete Medea Hypothesis Review Table of Contents is here.

The main theme of this post is a summary of biomass through time and that the Medea Hypothesis predicts that over time, biomass will fall from past peaks due to the interactions and evolution of life. This is based on Chapter 7 Biomass Through Time as a Test and takes a small amount from Chapter 8 Predicted Future Trends of Biomass in the book of the same title. Again, I am going to minimize the commentary until after. This is where it is actually hardest to do so since Ward relies very, very heavily on computational models. Now that I have had a lot more sleep since we all got sick and the holiday, plus some commentary from Carlos (thank you!), I have developed some pretty strong opinions on the subject. I will attempt to avoid interjecting them and save them for the criticism post…which is coming quite soon.

If the post seems a bit different than the others, it is in part due to the fact that it took a while to pull together everything so that I could write it. I took notes, rather than reading directly from the book, and had more time to ponder the narrative. That may be good or bad.

The Tolkienesque Decline of Biomass Through Deep Time

The Medea Hypothesis conjectures that life works in contrary to its own interests. In this case, biomass, it actually works over time to reduce biomass through its interactions with other life and the environment. Ward predicts that biomass was actually more in the past – two potential times, the Devonian, just after the evolution of forests and the the Cambrian, just after the evolution of animals – and has been in decline ever since. Ward does note that it is very difficult to measure biomass through deep time though. He suggests that there are proxies that work to be able to model life’s biomass.

Biomass is limited by several things, but there are three that Ward specifically identifies and elaborates on. The first is energy. If there is not sufficient energy coming into the system where life resides, there is a very little life possible. The second limiting factor is the amount of nutrients available. The difference between a bare rock environment and the soil of any temperature climate are excellent extremes: one is highly nutrient rich and supports a cast of living characters that is quite extensive and the other is very, shall we say, barren, in comparison. The final example item that Ward narrows in on that limits biomass is temperature. The Arctic has a far more limited biomass than does the tropics. Ward cites temperature as the reason.

Energy has increased over time as far as the sun’s input into the world which would argue that there is an increased biomass as related to the solar input. However, early life was not photosynthetic. A lot of it consumed the primordial chemicals that were left over from the world’s formation. This is supposedly an easier to consume form of energy than photosynthesis. Early life ran through and consumed all this easily available nutrients and caused a crash. Theoretically. A lot of this is based on modern conjecture and the modeling work of S Franck et al. To be discussed below. This caused a biomass crash until photosynthetic based energy systems take over. Because there was a crash, a life induced biomass reduction, this counts as a Medean Effect.

Nutrients tie into this. Life Ward claims that carbon dioxide is actually the most important nutrient and the one that is the biggest clue to biomass over time is actually carbon dioxide. He makes the argument that the higher carbon dioxide levels in the past were indicators of a high biomass. The reason that he argues this is that there was far more carbon dioxide – his key nutrient – therefore there was far more potential for life to exist. During the Pharenozoic, the CO2 levels have dropped significantly. This means that the potential for life – according to Ward – has dropped. The cause, Ward states is because life is slowly sequestering the carbon: carbon cycle is broken from his point of view (strongly implied). Ultimately, this will be what dooms life according to Ward: the CO2 will run out because life will have sequestered it all.

Temperature is the final of the three limiting factors that Ward discusses in some detail. This is the one that he talks about the most. He states that 70 C is the upper limit for life to exist and be productive on a large scale. 0 C is equally bad. The ideal from his point of view for biological productivity is between 20 C and 70 C. The Pharenozoic has had a temperature band of 15 C +/- 10 C on average. Trace evidence, especially isotope ratios and the types of minerals in the sediments are the evidence for the temperatures in the Pharenozoic.

According to Ward, the traditional view of the temperature evolution of the world went something like this. Around 3.8 billion years ago, the world cooled to around 80 C. It then cooled to approximately 40 C around 3 billion years ago. Sometime around 2 billion years ago it cooled to about 20 C: near the Pharenozoic temperature band. After that, never rose above 30 C.

He counters that new research using ‘pristine cherts’ – that not altered by subsequent geological events – indicate that the temperature changes were rather different than what the ‘traditional’ view is. The time steps with temperatures he cites are 70 C at three billion years, 60 C at 2 billion years, and 40 C at 1 billion years.

Ward then relies on Franck et al 2006/2002/2000 papers to back his claims on biomass. The microbial ecology that existed prior to the evolution of complex life is in the models as sustaining biomass at a higher rate than the subsequent ecologies. It was some form of steady state or near to it in their models. Their ideal temperature for productivity is 40 C. The actual peak of biomass according to the Franck et al model was just after the evolution of complex life.

[figure to be added on Sat]

Based on figure 7.3 from the paper, (see above, tomorrow morning), Ward argues that biodiviserity and biomass are divorced from one another. He goes on to use the Franck paper to to argue that life made jumps in biomass with each breakthrough in exploiting a new energy resource and that afterward a slow decline would take place until the next energy source was ‘found’ and exploited. He implies that there are no more energy sources to exploit for another breakthrough.

Part of his argument is wrapped up in the idea that at the time of the Edicarian/Vendian fauna there was a fundamentally different form of ecology present. The world was covered in bacterial mats. This is demonstrated through the Ediacarian fossils themselves. They were lain down in sandstone and that makes it terribly hard, if not impossible so says Ward, to preserve soft tissue like those fossils have. He uses a class of his to demonstrate how they were created. If there was a bacterial mat under the dead organism and then another ground on top when it silted over quickly, then you would be able to get the fossils as seen. Otherwise, they will decay and not produce fossils. Because bacteria were so common, and able to form the mats, the biomass was higher then. This is the proof that biomass was higher then.

Conclusion (for this post):

Ward then states that the biomass peak, in his opinion, was between the evolution of forests until the Eocene. This is a bit confusing because of what he argued just prior. Ward argues that life caused the temperature drop and that this is due to its Medean nature: by absorbing CO2 as it does, causing a breaking of the global greenhouse, life is dooming itself.

Post Epilogue:

That tackles the Ward’s arguments about biomass through time. He goes on to the next chapter describing what the future of biomass is. This is bound up in Franck et al’s model again. I think I will tackle that as a separate post. I have most of the notes already, but it needs a few more bits to make me even close to happy with it.

1 comment:

Anonymous said...

Of course, one could interpret the graphs of biomass and biodiversity representing the opposite trend; that as autotrophs become more and more efficient at fixing carbon dioxide into sugar from the atmosphere, more life was able to exist simply because more nutrients and energy were cycling around in the biosphere. An interesting idea related to this speculation is to see if there is any correlation between the rise of the C4 and CAM plants and the apparent Cenozoic spike in biodiversity (while the two may not be directly linked, it seems that one might have an effect on the other).

And as has been stated before in this review of the Medea hypothesis, grass and possibly other C4 plants were present before the PETM and Cenozoic drying, they just weren't that common for some reason. Once the world shifted to one that favored them over their kin, they ended up spreading out and dominating the global florasphere. This could be due to lower C02, or at the same time it could be that they were adapted to dryer climates, or in an inverse of Ward's hypothesis the fact that they could fix more C02 per unit of time than other plants may have given them more available sugar and energy. Its kind of funny though how groups that seemed to be going through an evolutionary radiation during the Late Cretaceous (mammals, squamates, neornithe birds, angiosperms) ended up becoming the dominant group of multicellular land organisms in the Cenozoic, while those that didn't (i.e. non-neornithe dinosaurs, pterosaurs, etc.) died out. Of course there are exceptions to this trend, like the mosasaurs who were going through a third radiation right up to the K-T, yet died out.

I'm also starting to doubt how much basis, if any, Ward's theory on why the archosaurs won out in the Triassic has. While a global dip in oxygen would make sure the P-T casulaties were notably lopsided towards synapsids, "amphibians", and pareiasaurs (add in the fact that we have no idea how diverse diapsids were in the Permian, most except Claudiosaurus known from scrappy remains), if Ward's theory of continual low oxygen during the whole of the Triassic is correct, then we'd expect the remaining synapsids to either shrink down into the mammal niche much earlier, or else get out-competed by the archosaurs. But this isn't the case, as large synapsids redeveloped from small (or relatively small) Permian survivors early in the Triassic, and indeed there were still some big synapsids romping around at the same time as the first dinosaurs (Placerias, Exaeretodon).
Add in the fact that the Triassic had some pretty big bugs, while not as ridiculously large as their Carboniferous kin, included such monsters as Nanotitan; a bug with a foot-long wingspan. One would not think that such a big bug could exist in Ward's hypothesized oxygen-poor atmosphere.