2 GAIA referred to Erwin Schroă dingers conclusion that life has the ability to move upstream against the flow of time, apparently paradoxically and contrary to the second universal law In fact, what is operating is a tightly coupled system to favour survival; energy is taken in (e.g., oxygen from the atmosphere is breathed), converted (e.g., stored body fats and sugars are transformed), and then excreted (e.g., waste products such as carbon dioxide are released back into the atmosphere) If the entropy of excretion is larger than the entropy of the oxygen consumed, life continues, despite the second universal law The Superorganism Concept There is difficulty in envisaging an eruptive planet with a molten core and other complex inorganic processes as a living superorganism However, the inspiring ‘whole-planet’ image of Earth as seen from space and the contrast between the environment on Earth and the environments on the moon, Mars, Venus, and Mercury have focused research on considering how the significant planetary differences arose, and in particular on the question of how and why the atmospheres differ The atmospheres of the Moon, Mars, Venus, and Mercury are a good starting point for comparisons to Earth, because the atmospheres are the least complex and most accessible of the zones of all these planets; indeed, the atmospheric compositions on other planets were known before space exploration commenced (see Solar System: Mars; Moon; Mercury; Venus) The Earth has an atmosphere of N and O, with traces of carbon dioxide, methane, and nitrous oxide, not in equilibrium, whereas the atmospheres of Mars and Venus are dominated by carbon dioxide and are in equilibrium If the atmospheres of Mars and Venus were heated, there would be no reaction with the surface materials, whereas heating Earth’s atmosphere would produce reactions leading to a carbon dioxidedominated atmosphere Lovelock concluded that the improbable atmosphere of Earth ‘‘reveals the invisible hand of life’’ The atmosphere contains oxygen and methane, which should react to form water vapour and carbon dioxide: that this does not occur, and that constant atmospheric compositions of these gases are maintained, reveal, Lovelock believes, that there is regulation by life (see Atmosphere Evolution) Scientists as early as Eduard Suess and Vladimir Vernadsky accepted that there was continuous interaction between soils, rocks, oceans, lakes, rivers, the atmosphere, and life Much later, Stephen Jay Gould stated that ‘‘organisms are not billiard balls, struck in a deterministic fashion and rolling to optimal positions on life’s table’’ Living things influence their own destiny in an interesting and complex, but comprehensible, way Thus the sum total of the physical state of a planet, with life, is a combination of the inanimate processes and the effects of life itself JZ Young said that the entity that is maintained intact, and of which we all form part, is the whole of life on the planet This statement really provided the link between theory and consensus, on the one hand, and Gaia concept, on the other, expressing as it does the view that the entire spectrum of life on the planet has to be considered alongside the geological and inanimate physical processes, if we are to understand how the planet works This, of course, has led to the present preoccupation in educational circles with ‘Earth System Science’ (see Earth System Science) Gaia goes further than Earth System Science, which is purely a holistic educational approach, in requiring a global system that has the capacity to regulate the temperature and composition of Earth’s surface, hydrosphere, and atmosphere, keeping it comfortable for living organisms Criticism of the Gaia Concept Criticism of the Gaia concept, once advanced, was by no means slight, and the Gaia model was not taken seriously by scientists, at all, until the early 1970s Fred Doolittle came out with the belief that ‘‘molecular biology could never lead to altruism on a global scale’’ – altruism by living organisms being apparently inherent to the concept Richard Dawkins in 1982 supported him: ‘‘the selfish interests of living cells could not be expressed at the distance of the planet’’ It was also remarked that Gaia lacked a firm theoretical basis Heinrich D Holland considered that biota simply react to change in the state of Earth’s nearsurface environment and processes, geologically produced, and those that adapt better survive: the rest not Many scientists saw Gaia as a teleological concept, requiring foresight and planning by organisms, something that the model surely never represented However, a major step was taken at the Chapman conference of the American Geophysical Union in 1988, when numerous papers on Gaia were presented: the question of the scientific testability of the Gaia hypothesis was raised Holland’s statement was really an oversimplification, because the environmental constraints to which an organism adapts can in no way be entirely inorganic in origin – geological processes are a combination of the inorganic and the organic Lovelock stated this when he objected that ‘‘life cannot have adapted solely to an inert world determined by the dead hand of chemistry and physics’’ The two main objections to Gaia were, first, the teleological one