2015 Feb 23 (birthday of grandPa Roy Christopher Lutes, 1895-1998, who very well understood)
No one may claim authority to define Gaia.
Having not seen a sufficient definition to cite, this is merely one's feeble/valiant effort.
Gaia is the name of the (primordial) Greek goddess of Mother earth.
Gaia was selected* by James Lovelock of the U.K. to name his theory of life on earth -
i.e. every atom is connected and influential in the whole.
Gaia is the realization that earth is a living being, relative to each and all of us, the consummate living being, our Mother, from which each of us derives, per universal, undisputed science.
Many of us grew up with a view of earth as an object. Gaia is for us the revelation of GOD. Many of us also grew up with the concept of nature. Gaia is more complete, a term referring to that which includes nature. Gaia is a superset of nature. It is the living homeostatic nexus of the celestial being, our common home in the exploding BANG.
The consequential religion for me is: we must first care for Gaia, then us the living, then me.
* Lovelock attributes Nobel Laureate neighbor William Golding for making the suggestion in 1967 to name his scientific theory of relation of all beings to the Mother planet; and to
"Lynn Margulis, who joined me in the development of Gaia in 1971. She put biological flesh on the bare bones of my physical chemistry. She has courageously supported Gaia in spite of hostility from parts of the United States"
"Gaia has been my inspiration since it first came into my mind in September 1965."
"Life does more than adapt to earth; it changes it, and evolution is a tight-coupled dance with life and the material environment as partners, and from the dance emerges the entity Gaia."
"Gaia is part of science and is therefore always provisional, but earth, which is its embodiment, is something real for us to respect and revere. ... Gaia is not an alternative to religion but a complement."
---- Homage to Gaia The Life of an Independent Scientist by James Lovelock, Oxford Press 2000
"A Christian who does not protect creation, who does not let it grow, is a Christian who does not care about the work of God, that work that was born from the love of God for us. And this is the first response to the first Creation: protect creation, make it grow."-- Pope Francis, Homily, Feb. 9, 2015
"We need to care for the earth so that it may continue, as God willed, to be a source of life for the entire human family." -- Pope Francis tweet on EarthDay April 22 2015