Gaian Bottleneck Astrobiology: The Case for Habitability

[jim mcnamara]

Astrobiology. 2016 Jan;16(1):7-22.
The Case for a Gaian Bottleneck: The Biology of Habitability.
Chopra A1, Lineweaver CH1.

Abstract
The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. Here, we present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.

The primary idea of the Gaia Hypothesis - Lynn Margulis - is controversial, so I expect this will be. But it may also be a way to answer to Fermi's question: 'Where are they?' - meaning why have we not detected intelligent life elsewhere in the galaxy.

 

[phinds]

Certainly an interesting way of looking at the issue. Kind of hard to test though, at this stage in our knowledge of other worlds. The mechanisms may or may not be as touchy as that quote implies.

 

[jim mcnamara]

Well, there was the Cryogenian era during the Neoproterozoic - snowball Earth along with a lot of subsequent mass extinctions. So, if for example, the Chixalub impact had been larger, then perhaps modern life might have been a reversion to 'refrigerator parasites' (to quote @Chronos term for single celled green things). https://www.physicsforums.com/threads/best-star-for-exoplanet.490503/#post-3720241

 

[Laroxe]

There seems to be a lot of assumptions in this, who says the universe isn't teaming with life? Why would this life need to control the surface environment? Indeed extinction may be the default, 99% of species that ever lived on Earth are extinct. However what is being increasingly discovered is that life can be extremely adaptable and can exist in some very hostile environments, the major lessons of extinction events on Earth is that once it is established it is extremely persistent. The questions about intelligent life are different, it seems based on the strange idea that life evolves towards a particular goal and that intelligence is in some way useful or valuable. The dinosaurs were around for a long time, far longer than it took for our intelligence to evolve, it was probably just a tragic accident. The problem with Gaia is it gives nature a personality with human motives and values, well in fact a very particular set of motives and values, its a fantasy. Then once you get around all the biology you've got the problems of motivation, who says they would want to meet us, and distance, maybe the speed of light really is the limit.

 

[rootone]

... maybe the speed of light really is the limit.

Special and general relativity have been tested by thousands of observations, and so far relativity is firmly standing.
Assuming that this obstacle is insurmountable, it is hard to imagine a motivation for any intelligent species to dispatch travellers knowing that they will never see the traveller again, and that the chances of the traveller arriving somewhere habitable within their lifetime are close to zero.

 

[Blank_Stare]

...and that the chances of the traveller arriving somewhere habitable within their lifetime are close to zero.

Let's assume that the technology were available - forget all the arguments that it can't work because this thing or that thing hasn't been invented. Let's just say that it's possible to send a ship to the stars.

Even if the chances of making it there in a single lifetime are zero, the concept of a "multi-generational farm ship" might still make the attempt appealing, under the right circumstances, and to the right group of individuals, or nations.

If, for the sake of argument, we imagine an Earth that has a run-away environment (not a stretch), and it becomes clear that our species will not be able to survive very much longer (also not a very big stretch) - the concept of saving our race, by sending them into space in a modern-day "Arc", knowing full well that they will never return to Earth (or if they do, will find it uninhabitable), and that only the offspring of several generations of ship's denizens will likely ever see a habital planet, if at all - I think we would choose the "Save the species" (not just humans, but as many lifeforms as we could figure out how to save), option. (I'm sure my English teacher is turning in her grave at that run-on...)

There is no argument that this would be a longshot. We spend so much time and energy arguing, and trying to exterminate one another, that we might never even get the ship built. For that matter, those who made it onto the ship might continue exterminating one another, and the mission could ultimately fail.

But I'd like to think we would at least try.

 

[Evo]

Too speculative, closed.