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by Ivan Cenzi

Some trillions of years ago a sloppy dirty giant
flicked grease from his fingers. One of these gobs of grease
is our universe on its way to the floor. Splat!
William S. Burroughs, Ghost of Chance, 1991

Developed in the 70s by James Lovelock and deeply criticised as an alleged form of vitalism, the value of the Gaia Hypothesis mainly resides in the debate that it has generated, more than in its actual legitimacy. Nowadays the presence of lifeforms on other planets is not regarded by scholars as a remote eventuality, but as a statistically possible occurrence; this change of perspective is partially due to the spreading of the idea that life could be able to find a stable balance on its own accord.
The Gaia Hypothesis was based on a series of observations. The sun, for example, during the last three–four billion years has gotten warmer and warmer, but life has been able to survive. It might be possible, suggested Lovelock, that the living organisms other that simply adapt to this global overheating, actively fought against it by cooling down the whole planet. Life, in fact, which is based on carbon, has sucked in the carbon dioxide from the atmosphere, reducing the greenhouse effect and compensating in this way the effects of the rising temperature.
A faultless system that Lovelock named after the Greek divinity representing the Mother Earth, the origin of life and of all creatures. Its optimistic view and catchy name played a big role, consecrating its fame in popular culture.
But the buzzkill is always around the corner.
In 2010 the palaeontologist Peter Ward, from the University of Washington in Seattle, advanced a counter-hypothesis which, beginning from its name, clashed with the Gaian one: the Medea Hypothesis.
And, thinking about what Medea did to her progeny, you’ll soon understand why it’s definitely less pleasant to have her as a mother.
According to the Medea Hypothesis, life on this planet has suicidal tendencies. The living organisms – postulates Ward – on the long run will cause their own destruction, and humans will not be the actual core of the problem.
It happened in the past: the methane poisoning (3.5 billion years ago), the oxygen catastrophe (2.7 billion years ago), snowball earth (both 2.3 billion years ago and, again, 790-630 million years ago), and various mass extinctions, including the Great Dying.
In short, every time Life was about to die out once and for all – if we do not consider the meteorite that caused the extinction of the dinosaurs – the life itself was the true responsible, and with life we mean the anaerobic microorganisms.
These bacteria live in oxygen-poor zones of the oceans, but as an effect of the global warming, they will begin to proliferate and release sulfuric acid, a killer gas which can destroy all lifeforms. Sooner or later one of the recurrent “suicide attempts” of the biosphere will be successful and will put an end to the planet’s life, a weird chemical experiment which was doomed to fail from the very beginning – warns us Peter Ward. And in terms of biomass weight (the weight of all living creatures) the planet Earth has already started its downfall: from now on the presence of life will relentlessly decrease.
Unless we take action. That’s right, the Medea Hypothesis might seem hopelessly pessimistic, but its consequences are set in a distant future (the rendezvous with the global extinction is in 500 million years). Moreover, Ward points out that, being aware of the actual state of things, we can take all necessary countermeasures in order to keep the level of carbon dioxide stable: not too much and not too little.

Basically, Ward’s message is that we could turn Medea into Gaia if we really wanted to.