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The Medea Hypothesis

The Medea Hypothesis, Is Life on Earth Ultimately Self-Destructive?, Peter Ward, 2009, Princeton University Press, Princeton New Jersey, ISBN-13: 978-0-691-13075-0

Peter Ward is professor of biology and Earth and space sciences at University of Washington, and an astrobiologist with NASA. He is a renowned paleontologist who appears regularly in Science documentaries on TV. In short he is a big gun.

In this book he looks at the flip side of the Gaia hypothesis. If Gaia was the Good Mother, Medea was very much the Bad Mother.

Gaia theory has a checkered history. When James Lovelock introduced the concept in 1979 it raised the hackles of establishment science. It has been reviled and refuted many times over to no avail; the refutations ended up being no such thing. Some parts of Gaia theory are now well established science; some are the subject of serious scientific work; and some are problematic.

Then there is the New Age pseudoscience and mythology. It would be irrelevant except for the human tendency to conflate very different things that go under the same name.

Ward identifies four major variants of the Gaia hypothesis, optimizing Gaia, Self-regulating Gaia, Coevolutionary Gaia, and Progressive Deterministic Gaia. He dismisses them as either being untestable, ergo unscientific, or else trivial. I disagree, but after all it is his book.

Ward's dragon of choice is Lenton's Evolving Gaia. Lenton's view is that life's ability to regulate the environment in life's favor evolves over time and becomes more effective. Over time life has become more resilent in responding to perturbations in the environment. The great advantage of this dragon is that it makes testable predictions or at least so Ward claims.

The Gaia hypothesis supposes that the living Earth is a good mother. Ward argues that the living Earth is, like Medea, a very bad mother. Ward advances the Medea hypothesis, to wit:

"Habitability of the Earth has been affected by the presence of life, but the overall effect of life has been and will be to reduce the longevity of the Earth as a habitable planet. "
As a thesis, this really doesn't work. To begin with, it is possible that if life had never developed Earth would not now be a habitable planet. Life stripped the greenhouse gasses from the atmosphere; without life Earth may have experienced a runaway greenhouse effect.

More importantly the future of Earth is simply not predictable. It is true that if humanity has no significant long term effect, and if we extrapolate the loss of atmospheric CO2 indefinitely, and if there are no other perturbations or evolutionary surprises, then it appears that the biosphere will collapse due to CO2 starvation some hundreds of millions of years from now. There are too many imponderables here to make any kind of reasonable prediction.

However it is fairly clear from the text that Ward is not arguing for his nominal thesis. Instead the thesis that he argues for is something like this:

Earth has an intrinsic set of well-behaved geophysical cycles that produce an environment that is favorable for life. Life's impact on these cycles is to introduce instabilities that occasionally become catastrophic.
To this end Ward lists a number of catastrophes and upheavals.

They include:

  • The Methane Disaster (3.7 Billion years BP). Methane producing life (stromatolites) cooled that planet with a methane haze that was balanced by volcanic heat. It is not clear to me why he calls this a Medean event.
  • The Oxygen Catastrophe (2.5 Billion years BP). According to recent work by Kirschvink the evolution of life that could live in the presence of oxygen occurred well after the oxygen rise.
  • Snowball Earth I (2.3 Billion years BP). Life stripped CO2 and Methane from the atmosphere which lead to runaway glaciation.
  • Canfield Oceans (2 to 1 Billion years BP). Canfield oceans are not a type of solitaire. Rather they are anoxic oceans with H2S poisoning due to carbon-sulfur bacteria that bloomed occasionally in post oxygen Earth. Besides H2S poisoning said bacteria also inhibited nitrogen compound formation.
  • Snowball Earth II (700 Million years BP). Eukaryote plant bloom stripped CO2 again. This one is credited with spurring the development of animal life.
  • Reduction in microbial life (600 Million BP). Animals were a one-two punch to microbial life. Animals ate microbial slicks. Animal fecal pellets fell to the ocean bottom and out of the effective biosphere.
  • Phanerozoic microbial extinctions (to present). Numerous global warming events leading to anoxic oceans and Canfield events at 490, 360, 251, 201, 190, and 100 million years BP.
This is an impressive and interesting list, but one has to ask:

What does it all mean for Medean and Gaian hypotheses? In my view, perhaps not much. Clearly life has a major impact on the global climate. From time to time there are major extinctions, often followed by major reorganizations of the biosphere phase changes, so to speak.

What it comes down to is that on the large scale, life does not act to preserve current conditions. Rather life's impact leads to bloom and bust cycles on geological time scales. To date, the evolutionary potential of life has had enough resilency to survive and prosper. Is this Medean? That is a matter of perspective; one can look at bloom/bust/phase change as Medean (which it certainly is for life forms undergoing the bust) or can one can take the view that that is how the system works.

And what of Gaia? There is some truth to the idea; in the short run ecologies tend to stabilize. To paraphrase the old saying, the history of life is one of long periods of mind numbing sameness interrupted from time to time by frightening disaster.

And what of the long term habitability of Earth? Phase changes happen. Sometimes they come out of the Earth in the form of massive vulcanism. Sometimes they come out of the sky in the form of killer asteroids. And sometimes they come out of East Africa in the form of bipedal hominids.

Either we and our descendents will be around for the long run or the intelligences that we create will be. We stumbled onto the keys of life and the ability to turn them in lock of being. In the long run the habitability of Earth will be shaped by what we do.

That is the long run. At present we are not capable of using our intelligence for the long term benefit of ourselves and the world we inhabit. In the short run we are making a mess of things and we and the biosphere will probably pay a high price.

The old order passeth. All that was no longer is, and never again shall be.

This page was last updated July 1, 2009.
Copyright © 2009 by Richard Harter

Richard Harter's World
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July 2009