The Cosmic Gaia Hypothesis and the Copernican Principle

As a geological fellow traveller, I have always been interested, I would say extremely fascinated, by the seemingly symbiotic interactions between earth systems and biological systems.

David Grinspoon writes a truly thought provoking article for Nautilus on this topic, which is adapted from a just published book of his. In this article Grinspoon outlines what we might refer to as “the cosmic Gaia hypothesis” of which the Gaia hypothesis that we know is a special application to the Earth.

I myself do not regard the Earth as literally alive, I should stress at the outset but do hold to the Gaia hypothesis.

Should the cosmic Gaia hypothesis be a defensible thesis then we would have, it seems to me, another application of an even more general principle, namely the Copernican Principle. The cosmic Gaia hypothesis might also have implications for the Anthropic Principle, and It might tell us something about the Anthropocene arguably the current geological era.

Let us examine some key premises underlying the Grinspoon cosmic Gaia hypothesis. Grinspoon writes of what he calls the traditional Darwinian view where, “Earth was essentially a stage with a series of changing backdrops to which life had to adjust.” This is akin to Newton’s view of an absolute space and time that serves as the stage upon which matter and the forces of motion strut their stuff.

But the Gaia hypothesis, like General Relativity, eclipses this view for life itself influences the Earth much as matter and energy influence the geometry of spacetime.

The Gaia approach, prompted by the space-age comparison of Earth with its apparently lifeless neighbors, has led to a deepening realization of how thoroughly altered our planet is by its inhabitants. When we compare the life story of Earth to that of its siblings, we see that very early on in its development, as soon as the sterilizing impact rain subsided so that life could get a toehold, Earth started down a different path. Ever since that juncture, life and Earth have been co-evolving in a continuing dance.

As a geological fellow traveller who grew up in Western Australia the most familiar example of this was once close to home, namely the oxygenation of the atmosphere

The Gaia approach, prompted by the space-age comparison of Earth with its apparently lifeless neighbors, has led to a deepening realization of how thoroughly altered our planet is by its inhabitants. When we compare the life story of Earth to that of its siblings, we see that very early on in its development, as soon as the sterilizing impact rain subsided so that life could get a toehold, Earth started down a different path. Ever since that juncture, life and Earth have been co-evolving in a continuing dance.

The most far reaching application of the Gaia hypothesis, by no means a sure bet as Grinspoon states, is to plate tectonics

By controlling the chemical state of the atmosphere, life has also altered the rocks it comes into contact with, and so oxygenated the crust and mantle of Earth. This changes the material properties of the rocks, how they bend and break, squish, fold, and melt under various forces and conditions. All the clay minerals produced by Earth’s biosphere soften Earth’s crust—the crust of a lifeless planet is harder—helping to lubricate the plate tectonic engine. The wetness of Earth seems to explain why plate tectonics has persisted on Earth and not on its dry twin, Venus. One of the more extreme claims of the Gaia camp, at present neither proven nor refuted, is that the influence of life over the eons has helped Earth hold on to her life‐giving water, while Venus and Mars, lifeless through most of their existence, lost theirs. If so, then life may indeed be responsible for Earth’s plate tectonics.

Life does not exist on a habitable background stage, but itself is responsible for creating the conditions of its own habitability. What makes Grinspoon’s account of the Gaia hypothesis a general principle is that life exists on a planet at a planetary scale, not in isolated pockets, and influences the macro processes of its home planet in ways that fosters that planets habitability. A planet is either “dead” or it is “alive,” there is no half way house. If life is to be found in the universe it will be found on planets teeming with life, and in which life exists as a planetary scale force.

Gaian thinking has crept into our ideas about evolution and the habitability of exoplanets, revising notions of the “habitable zone.” We’re realizing that it is not enough to determine basic physical properties of a planet, its size and distance from a star, in order to determine its habitability. Life itself, once it gets started, can make or keep a planet habitable.

So,

I believe that only a planet that is “alive” in the geological sense is likely to be “alive” in the biological sense. Without plate tectonics, without deep, robust global biogeochemical cycles which life could feed off and, eventually, entrain itself within, life may never have been able to establish itself as a permanent feature of Mars, as it did on Earth

Grinspoon cites a colleague to great effect here,

As my colleague Colin Goldblatt, a sharp young climate modeler from the University of Victoria, once said, “The defining characteristic of Earth is planetary scale life. Earth teaches us that habitability and inhabitance are inseparable.”

There is a whiff of the Copernican Principle at play here. The Earth is not “special” with almost unique characteristics that makes it habitable, rather life, once it gains a foothold, structures the habitability of a planet and so life takes on a planetary scale. This is a general principle of biological or ecological systems.

It seems to me that this notion of self creating habitability weakens the Anthropic Principle as the Anthropic Principle very much proceeds upon the basis of the traditional Earth, or nature itself, as background view of habitability.

Of course, geological processes have not been so friendly to life. The Permian mass extinction, the most far reaching culling of life on Earth, occurred due to large scale volcanism, which some attribute to the rupturing of a “hot spot” through the continental crust (in today’s Siberia). Life itself, as demonstrated through the paradigm example of oxygenation, can be responsible for its own extinction as it alters Earth processes.

Which, of course, brings us to the Anthropocene. The example of oxygenation suggests to us that life’s transformation of planetary scale systems can be lethal. Humans, as demonstrated by the crisis of biodiversity, are responsible for a major assault on the habitability of the Earth, an essential feature of the Anthropocene, suggesting to us that intelligence might be an evolutionary dead end.

Surely it would be irony should a species evolve intelligence enough to come to know of Gaia, come to know that it is killing Gaia, yet do little or nothing to arrest the atrocity as atrocity it is.