The Medea Hypothesis
Is Life on Earth Ultimately Self-Destructive?
Peter Ward, 2009, Princeton University Press
I'm conflicted about this. Ward's claim is that life contributes to positive feedback cycles that push the Earth away from equilibrium, to the detriment of life. My guess is that he is assuming linearity, and that maximization of biomass (or bioactivity, not the same thing) is the optimum goal.
Certainly life can exponentially amplify small variations, but all amplifiers saturate, nonlinearities dominate, and the amplification factor drops to 1.0. Algae in a pond; it grows until it encounters nutrient limits, and the dying algae may make the pond unlivable for algae and many other organisms. For a while; perhaps until another organism thrives in the "dead" pond, changing the conditions back to those that foster algae. Cycles and oscillations are part of life.
Quantity of biomass? There may be some minimum level of biomass below which no life cannot propagate. Above that hypothetical level, organisms adapted to those conditions are unadapted to more abundant times; humans of this current geological era could not survive in most prior eras, even if those had more biomass.
- p68 Ward describes the 360 Mya Devonian mass extinction as due to ocean eutrophication and global anoxia, possibly involving massive releases of hydrogen sulfide (H₂S).
- p76 (Don) Canfield ocean, anoxia, H₂S from sulfur bacteria kills nitrogen-fixing bacteria and limits total life.
- p80 - a graph of continental area vs time; almost none in the Archaean 3 GYa, 30% now, 50% 1.6 Gy later. Presumably after that, plate tectonics slows or stops and the continents erode away while the temperature climbs. The graph shows us at an average surface temperature of 15C, with temperatures exceeding 40C 0.5 GYa and 1.0 GY later.
Ward warns us that we will probably turn into global consumers with two cars in every garage, and CO₂ exceeding 1000 ppm. Similar extrapolations in 1900 would have us knee-deep in urban horseshit. The automobile was the first "environmental solution" attractive to consumers - there will be more, designed for convenience, with emissions-reduction an unimportant side effect.
Ward ends on a positive note - human geoengineering, or migration.
Now that humans are here, we may render the world uninhabitable for humans, but we lack the power to sterilize the Earth. And if we did, we would also have the power (used differently) to preserve the world (or some of the life now on it) well beyond its natural span. Let's hope we wise up.
My brainfart: in the very long term, the Sun will expand and overheat, and bake the Earth if it orbits at 1 AU. However, we direct all of the asteroid belt (in small chunks) into the Moon, the angular momentum of the belt can be transferred to the Earth-Moon system, increasing the radius of the orbit around the Sun. We might also do this with close flybys from objects dropped from the Oort cloud, each transferring angular momentum before plunging into the Sun. This will involve great precision and great patience, but the raw material (mass and angular momentum) is out there.