7.2: What is the Gaia hypothesis?
Description
This article is from the Scientific Skepticism FAQ, by Paul Johnson Paul@treetop.demon.co.uk with numerous contributions by others.
7.2: What is the Gaia hypothesis?
There are several versions. The following taxonomy was suggested by
James Kirchner in "Scientists on Gaia":
* Influential Gaia: the biota has a substantial influence over certain
aspects of the abiotic world
* Coevolutionary Gaia: the biota influences the abiotic environment, and
the latter influences the evolution of the biota by Darwinian processes.
* Homeostatic Gaia: the interplay between biota and environment is
characterized by stabilizing negative feedback loops.
* Teleological Gaia: the atmosphere is kept in homeostasis not just by
the biosphere, but in some sense "for" the biosphere.
* Optimizing Gaia: the biota manipulates its environment for the purpose
of creating biologically favorable conditions for itself.
I'd say no one disputes Influential Gaia, and no serious scientist
supports Optimizing Gaia (though some of Lovelock's earlier remarks
tend in that direction). Most of the scientific debate surrounds
Coevolutionary and Homeostatic Gaia. Some point to Le Chatelier's
principle (a system in equilibrium, when disturbed, reacts to as to
tend to restore the original equilibrium). However the ice ages
suggest that the Earth is not in long-term equilibrium.
References:
For a range of interesting perspectives on the Gaia hypothesis, see
the SF novel "Earth" by David Brin.
James Lovelock, "Ages of Gaia", W. W. Norton, 1988.
"Scientists on Gaia", ed. by Stephen Schneider and Penelope Boston,
MIT Press 1991.
The latter book is a collection of papers presented at an American
Geophysical Union Symposium in 1988. Most are technical, but the
introductory papers are eminently readable. The whole range of
scientific opinion is displayed, from Lovelock and Margulis to
critics such as James Kirchner.
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