This is my third post in my consideration of The Medea Hypothesis. I am trying to go through and summarize what Dr Peter Ward puts forward as the hypothesis and what proof he is basing it on.
My previous posts are here and here.
The Medea Hypothesis review is complete and the table of contents is here.
The basic premise of the Medea Hypothesis is that life is suicidal and will exterminate itself by resource overuse and that it produces far more, or induces far more, positive feedbacks than correcting negative feedbacks. The negative feedbacks, he feels, are absolutely necessary for the Gaia Hypothesis to work. The Medea Hypothesis is a reaction to the Gaia Hypothesis and proposed as an alternate.
Ward proposes that certain events in the evolution of life, in deep time, that support the Medea Hypothesis. I am going to run through them now. I will quote as much as possible and try to summarize otherwise. This is by and large encapsuled in Chapter 5 of his book.
I am going to make a comment. I cannot help it. Forgive me. I have been trying to save it for the end. However, I think in this chapter, Ward moves his goal posts. Before he talked about biomass being decreased over time and now he's stating, in Chapter Five, that biodiversity is actually the key: "Let us begin this chapter witha first proposal about what will be called Medean events - life-driven episodes that result in a drop in the diversity of abudandance of subsequent (later generation) life." (pgs 72-73)1. DNA Takeover: 4.0(?) - 3.7(?) Billion Years Ago.
"Unfortunately, unlike the later events, which are based on data from stratal and fossil evidence, this first Medean event is no more than an educated guess. Many of us believe it to be true, although since ther is currently no way to scientifically test this hypothesis, it must remain an educated guess, and no more.
"Over the past several years, biochemists conducting experiments to find possible alternatives to our familiar Earth life have attempted and in some cases have succeeded, in producing DNA with exotic "languages," obtained by changing the number of nucleaotides used to code for a specific amino acid. Thus it is possible - indeed, I believe likely - that early DNA life on Earth might have come in a vaierty of forms, perhaps all slightly different from our now familiar DNA. If so, it is probable separate kinds of DNA competed against each other. [...] [I]t is probable that there would have been intense competition betweene ach of the kinds of DNA, competition that would have been inherently Darwinian. The suppression of other kinds of life would have followed, and if so, this would have been a Medean Event, in fact, the first example of a Medean event: the takeover of a single kind of life. Elsewhere I have followed other evolutionary biologists in supposing that the highest diversity of life, the most basic kinds of life, not species was surely early in Earth's history. "
pgs 72 -73.
In essence, boiled down, that our variant of DNA life outcompeted the other versions of life, whatever they may have been or even if they did exist, makes it Medean. It reduced the potential of life in the future by being competitive such that it wiped out everything other than itself.2. The Methane Disaster, 3.7 million years ago
(ought to be 2.7 billion years)
"The methane atmosphere hypothesized to have been present on the early Earth may have been a byproduct of the first life, a waste product of its metabolism. Life was present as a series of oil-like slicks and stacked bacterial layers and sediments, called stromatolites. Although individually small in size, these microbes became globally abundant and in so doing began to change the planet. This is the conclusion of the eminent atmospheric scientist and astrobiologist James Kasting
of Penn State. His new work describes how the formation of methane-producing life on Earth nearly ended the saga of life on our planet in its earliest epochs by creating a cold buffer on the surface of the planet. The formation of the methane haze took an already cold world (the Sun was more than 30 percent less energetic) and added a layer of clouds for the first time that reflected heat back into space. But for the very high volcanic heat flow on our planet, this type of condition made the planet much worse for life's survival. [...] In any event, this by-product of cooling clouds is not the predicted course of events under the Gaia hypothesis. This is the first test that shows how earliest life nearly ended its own history through its formation."
pgs 74-75, Chapter Five: Medean Events in the History of Life.
The paper which Ward is basing his conclusion on this paper
. This is one that I will be commenting on later. I added the link to Dr Kastings' page.3. The Rise of Atmospheric Oxygen, 2.5 Billion Years Ago - Chemical Weapon of Mass Destruction.
This is simply the oft talked about Great Oxidation Event
. Life developed 'modern' photosynthesis. The oxygen poured out to wipe out or marginalize most the rest of life. Ward states:
"Oxygen caused a massive mass extinction on planet Earth: the biovolume of life on the planet plummeted. This is a Medean result. Only the children of the bugs that could tolerate oxygen - and the cyanobacteria that learned to make it, and the bugs that later learned to breath it - would thereafter enoy the sunlight."
Pg 754. The First Global Glaciation, 2.3 Billion Years Ago - Life Causes the First Snowball Earth
The idea is that life developed photosynthesis and it sequestered the carbon to such a degree that this 'broke' the early greenhouse that warmed the earth under the fainter sun: the sun let off a nontrivially lower amount of radiation. This is normal for a star's evolution. This caused the near world coating ice age that has been proposed as one of the Snowball Earth
events. The Snowball Earth event would have nearly wiped out life. Because it did and had the potential to do so, if it was caused by life, it was a Medean Event. Ward states that it was.5. The Canfield Oceans, 2 - 1 Billion Years Ago (?)
The so-called Canfield Oceans are particular state that the oceans have developed into a few times through Deep Time. The oceans become stratified: that is that they differentiate into different levels that do not mix. When this happens, the lower depths become hypoxic - low in oxygen - and can often even become anoxic: lacking oxygen almost altogether. When this happens, certain types of anaerobic bacteria settle in to grow. One of these types of bacteria produces a very nasty chemical, hydogen sulfide. Hydrogen sulfide is very, very toxic. It kills most other life. Ward maintains that this dominated and existed for nearly a billion years - and in several mass extinctions - is a Medean Effect.6. The Second Snowball Earth, 700 million Years Ago
Ward maintains that life, once again, caused the second snowball earth scenario 700 million years ago and that it was made worse by the increased continental area: this had the potential to wipe out life and was "caused" by life. Medean effect again.7. The Rise of Animals, Reduction of Life, 600 Million Years Ago
Ward maintains here that the rise of animals with their carnivorous and herbivorous ways reduced life by taking nutrients, carbon specifically, out of the nutrient cycle. Animals were so effective at this that they caused a drop in the atmospheric CO2 content and a massive reduction in global temperature.
The rise of animals that so spectacularly ocured during the 540-500 million year-old "Cambrian Explosion" is deemed one of the great evolutionary events ever to have affected the Earth. Clearly the number of species on the planet radically increased. But what of the biomass? Just the opposite seems to have occured. Concomitant with the rise of animals and higher plants, there is a drastic reduction in the number of stromalites and other evidence of layered bacterial slicks. The evolution of herbivores and carnivores among the emergent animals was a major reasons for this. The fecal pellets of the newly evolved zooplankton - little animals that feed on plankton and other microorganisms - stuck together and formed slime balls that readily sank down to the abyssal depths, removing organic carbon and nutrients from being recycled by way of photosynthesis. Thus, we can view the evolution of complex life on our planet as Medean since it led to a reduction in the total biomass.
This biomass reduction was probably caused not only by herbivorous success of the newly evolved animals. There may have been a significant drop in global temperature as well - in fact the largest single drop in planetary temperature in Earth history, if the modeled results are correct.
Note: this is based on Franck et al 2006 which is based on Franck et al 2002. There will be a critique of this later.8. The Phanerozoic Microbial Mass Extinctions, 365 - 95 Million Years Ago
[really ought to be described as the return of the Canfield Oceans by Ward
Ward lays the blame for the Devonian, Late Triassic, and Permian Extinctions - as well as several lesser mass extinctions at the door of Canfield Oceans. He feels that the hydogen sulfide by-product of microbial life is the primary kill mechanism for these extinctions. That is a Medean Effect.9. Rapid Global Temperature Changes Due to Colonization of Land by Plants, 400 - 250 Million Years Ago
Plants colonized the land and as they adapted to their new environment they started doing two things. The first was that they started sequestering more and more carbon, especially through the carboniferous period (which I spoke of here) and also because they promoted the weathering of rocks far faster and that in turn caused the carbon dioxide to be drawn down as well. This caused global cooling on a massive scale and that in turn caused glaciations. Life became harder, the environments for ocean life was reduced (because the continental shelves were exposed because of the glaciations) and the amount of carbon available for life became less. This would be Medean behavior.10. Devonian Eutrophication Events, 360 Million Years Ago
Eutrophication events are ones where algae or plankton bloom in response to greatly increased nutrients in the waters. When this happen, they boom so greatly that they actually deplete the nutrients. This causes a die off and the bodies of the plankton and whatnot fall to the ocean floors. This in turn causes the ocean bottoms to slowly be rendered anoxic. Slowly, but surely - at least theoretically - life would slowly turn the oceans anoxic up to a very high depth, even in the absence of high temperatures. Ward maintains that this happened on a massive, even global scale during the Devonian, possibly as a response to the greatly increased nutrients coming off the continents from relatively recently developed forests. Ward maintains this helped drive the Devonian Mass Extinctions, ff this were true, then this would be another example of a Medean Event.11. The KT Extinction, 65 Million Years Ago
By the end of the Cretaceous there were planet-spanning forests. One effect of the [Chicxulub Impact] was the ignition of continent spanning forest fires. This produced an enmorous amount of ash that filled up the atmosphere. This soot, a product of life, caused global cooling for some months after the impact, which seems to have played a significant role in the kill mechanism. Again, a Medean Effect.12. The Pleistocene Ice Ages
Ward blames them on the draw down of carbon dioxide from the atmosphere by life.13. Humanity.
Ward states we are the ultimate Medeans. He dedicates a whole chapter to us.
That wraps up the What Is Medean Life Part Three. Next up is biomass through time and the future of life. Sorry this is taking so long. Life is...busy. Commentary will followafter the next post.