GAIA GAIA G J H McCall, Cirencester, Gloucester, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction The Gaia concept has evolved in the 30 years since it was first introduced by James Lovelock, an independent scientist and inventor It was initially a rather vague model relating to the climate and diversity of the planet Earth, though living organisms were critical to it The workings of the model were initially unspecified The concept, however, was one of a ‘superorganism’ operating to ‘regulate’ the planet, especially its surface temperature, yet lacking the ‘foresight’ possessed by intelligent animals Lovelock updated his work in 2000, publishing The Ages of Gaia The discussion here is based on this later book, and it is quite unavoidable to echo much of what Lovelock has said, because he is the only and definitive source Gaia in the Twenty-First Century Gaia is essentially about life, because life is seen to combine with inanimate processes on Earth, affecting and even regulating the physical state of the biosphere Lovelock found it surprisingly difficult to find a good definition of ‘life’ Of the definitions found in Webster – ‘‘the property of plants and animals (ending in death and distinguishing them from organic matter) which makes it possible for them to take in food, get energy from it, grow etc.’’ – and in Oxford – ‘‘the property which differentiates a living animal or plant or a living portion of organic tissue, from dead or non-living matter; the assemblage of the functional activities by which this property is manifested’’ – neither is satisfactory, and the second is tautological in the extreme To the first might be added, before ‘‘etc.’’, the words ‘‘and move, in the case of animals’’ Lovelock added to his definition of life that ‘‘living things use energy directly from the Sun and indirectly from food’’ (see Origin of Life) There is no difficulty in accepting that advanced living animal organisms, such as humans, are made up of intricate communities of connecting cells, and, as Lynn Margolis has shown, that cells are derived from micro-organisms that once lived free (see Precambrian: Prokaryote Fossils; Eukaryote Fossils) Larger entities, such as ecosystems, are also accepted, and space exploration has contributed to this understanding by allowing the entire planet Earth to be viewed from space The Gaia concept likewise involves envisaging the entire globe as an integrated system, with the atmosphere, the seas, the rivers, and the rocks interacting to modulate the planet’s physical state and thus the environment in which life can exist, with the presence of life contributing significantly to the interactions Gaia is thus not a synonym of ‘biosphere’ or ‘biota’: it is a much larger entity When the Gaia model was originally proposed in the 1970s, it was considered that the atmosphere, oceans, climate, and crust of Earth were regulated to maintain a comfortable state for life to exist, by and for the biota Temperature, oxidation state, acidity, and certain aspects of the rocks and waters were kept, at any time, constant, maintained in homeostasis, by the organisms at Earth’s surface This concept is now seen to have been incorrect, because both life, which is continually evolving, and the geological environment are in a state of constant change, and the conditions needed to maintain life change very rapidly, with the changing needs of the biota, so homeostasis cannot be maintained for more than very brief periods in Earth history The Earth is thus seen as being like a helicopter, which is, unlike a fixed-wing plane, never in stable flight The changing and evolving needs of the biota require that the brief periods of homeostasis are quickly overtaken by new requirements The concept now is of a superorganism in which the active feedback processes operate automatically, so that solar energy maintains comfortable conditions for life Molecular Biology: The Laws of the Universe Lovelock regarded the emergence of the science of molecular biology – embodied in the informationprocessing chemicals that underpin the genetic basis of most life on Earth – as having taken life science out of a routine classificatory and descriptive pursuit into a new and exciting study of how all the components in life are related Equally important are physiology, the study of organisms seen holistically, and thermodynamics, a branch of physics dealing with time and energy, connecting living processes with universal laws Two fundamental universal laws of physics are that (1) energy is conserved, however much it is dispersed, and (2) energy is always abating Hot objects cool, but cool objects not heat up spontaneously; water flows downhill, but not uphill Once used, energy cannot be recovered Natural processes always move towards an increase in disorder, which is measured by entropy; entropy expresses the tendency to burn out Looking at the relationship between life and entropy, Lovelock