James Lovelock's "Gaia theory" showed that the Earth, its rocks, oceans and atmosphere and all living things are part of one great organism, evolving together over the vast span of geological time. He elaborates here the basis of a new and unified view of the Earth and life sciences, discussing recent scientific developments: the greenhouse effect, acid rain, the depletion of the ozone layer and the effects of ultraviolet radiation, the emission of CFCs and nuclear power. Using the imaginary planet Daisyworld as a model, he demonstrates the geophysical interaction of atmosphere, oceans, climate and the Earth's crust, regulated comfortably for life by living organisms using the energy of the sun. The Gaia theory is seen to force a planetary perspective and concentrates on the health of the planet, rather than individual species of organisms. This hypothesis raises philosophical and religious questions which Lovelock tackles in a chapter on "God and Gaia". James Lovelock has also written "Gaia: A New Look at Life on Earth" and "The Greening of Mars".