The GAIA Hypothesis, most simply expressed is that: "The Earth is Alive". The Gaia Hypothesis conjectures that our planet functions as a single organism that maintains conditions (not unlike homeostasis in humans) necessary for its survival. Formulated by James Lovelock in the mid-1960s and published in a book in 1979, this controversial idea has spawned several interesting ideas and many new areas of research. While this hypothesis is by no means substantiated, it provides much to ponder about the symbiosis of physical, chemical, geological, and biological processes on Earth. In short, it is a very pretty hypothesis.

One thing making the theory pretty is that it seemingly forces a conjunction to occur between what I will call the spiritual and the scientific belief systems. These belief systems have evolved for centuries in a sort of détente, with an unspoken agreement to be non-antagonist to each other (unless one went too far, like Galeleo). On the spiritual side is the concept of Mother Earth that we have all heard, simply because it has been very much a part of human culture (part of our brief existence as a species) in myriad forms. The concept was central to the religion of Native Americans and is prominent in Hinduism as the goddess Kali. It is perhaps the ancient Greeks who had the best metaphor. They named their Earth goddess Ge or Gaia. An embodiment of the notion of a Mothering Earth, the source of the living and non-living entities that make up the Earth. Both Kali and Gaia was gentle, feminine and nurturing, but also ruthlessly cruel to any who crossed her. Gaia was the Greek goddess who drew the living world forth from Chaos. The prefix "ge" in the words geology and geography is taken from the Greek root for Earth. I believe it is fair to say that the concept of Mother Earth has been omnipresent and ubiquitous in human history, and anything but "new age".

I'm sure that most of us can see how such a spiritually framed concept could be difficult pill for some scientists to swallow, creating controversy. Regardless, the hypothesis persists. My own viewpoint is that it is not unlike Einstein's search for a Universal Field Theory, a set of natural laws equally applicable to systems of any size, from sub-nuclear to cosmic. Let's look of some of the many facets involved in Gaia.

A primary tenet of GAIA is reciprocal interaction between everything on Earth and the Sun. The sun interacts with life (primarily through photosynthesis) and life interacts with rocks (primarily in soil making). The Earth's mantle transmits nutrients to the surface through volcanoes, particularly at spreading ridges, and reciprocally, the earth's crust feeds the mantle at subduction zones. The diving plates at subduction zones also make the andesite and granite associated with subduction.

Much of Earth is indeed governed and caused by life. Level bottom marine habitats with soft sediments deeper than wave base, have sediment entirely made by the biota. Wherever waves affect things (sandstones and the like) sedimentology plays a role, but not in any fine grained sediment -- these in rocks are fine limestones and shales. Thus the structure of most marine rocks is biologically determined. Terrestrial rocks (e.g., the badlands of South Dakota) are a series of soils formed on overbank deposits and so, being soils, most of the structure is biologically determined. Hence, most marine and terrestrial rocks derive their structure biologically. Also, life controls both the much high free oxygen and small free Carbon dioxide levels of our atmosphere. Our atmosphere composition is inextricably liked to the atmosphere, that life maintains. Plate tectonics is enabled because the plates cool and can subduct. Before life diminished the carbon dioxide, the planet was hot owing in part to a greenhouse effect, suppressing subduction (like the lifeless planet Venus is today). Hence, plate tectonics also is biologically caused, with profound importance to life. Degassing is most prominent at spreading ridges and this would supply much nutriment. Most mountain building is caused by plate tectonics, so, in effect, life caused plate tectonics.

In summary, the GAIA hypothesis says that the temperature, oxidation, state, acidity, and certain aspects of the rocks and waters are kept constant, and that this homeostasis is maintained by active feedback processes operated automatically and unconsciously by the biota.

Or, as Darwin put it:

"whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved."