Are we special? Rare Earth probably most elegantly expresses the view that intelligent life exists only on Earth, and not elsewhere in the Universe. For an opposite view, including the Quarantine Model, see: http://www.exopolitics.com ===== >>Take that, Copernicus: RARE EARTH: WHY COMPLEX LIFE IS UNCOMMON IN THE UNIVERSE. By Peter D. Ward and Donald Brownlee. Springer-Verlag; 362 pages; $27.50 and œ12.50 THANKS to the work of Copernicus, Galileo and others, the earth long ago lost its place at the centre of the universe. Instead, it is now known to be just one of several planets orbiting one of hundreds of millions of stars in one of billions of galaxies. On the cosmic scale, there is nothing special about our planet after all. Not so fast, say Peter Ward and Donald Brownlee, a geologist and an astronomer respectively at the University of Washington. Instead, they suggest that "the continued marginalisation of earth and its place in the universe should be reassessed." They offer a powerful argument that the earth is, in fact, extremely unusual. That in turn implies that complex extraterrestrial life forms may be far rarer than science fiction stories and many scientists would have us believe. This claim might seem at odds with recent discoveries which suggest (at least to those investigating such matters) that extraterrestrial life could be commonplace. On earth, "extremophile" bacteria have been discovered that are capable of thriving in extreme and inhospitable conditions such as inside scorching geothermal vents and even inside rocks where life was previously thought to be impossible. This is surely grounds for optimism that bacteria could also live happily in other unlikely places, such as on Mars or in the oceans of Jupiter's moon Europa. In addition, the discoveries since 1995 of dozens of planets orbiting nearby stars suggests that planets are abundant, so there should be loads of places for life to get started beyond the solar system. Mr Ward and Mr Brownlee argue, however, that while primitive microbial life may well exist throughout the universe, the more complex organisms that evolved on earth owe their existence to an unusual combination of factors. If so, the estimate of Carl Sagan, for example, of a million civilisations in this galaxy alone looks vastly overdone. It is fortuitous that the earth orbits a star that is not too close to the centre of the galaxy (where cataclysmic events and dangerous radiation would prove hostile to living beings), but not too near the edge either (where the heavy elements needed to form planets are less abundant). It is lucky also that the sun is a solitary, stable star and the earth has a stable orbit around it. Just as fortunate is Jupiter's helpful hoovering up of many (though not all) potentially lethal comets and asteroids, and the fact that Saturn is small enough not to have ended up in a gravitational tussle with Jupiter that might have caused the loss of the solar system's other planets. Earth's chemical composition is also just right to allow plate-tectonic activity, which is lacking on both Venus and Mars, and helps to maintain the climate so that it is suitable for the long-term presence of liquid water. But perhaps the most important and yet unlikely factor is the earth's unusually large moon, whose presence has played a crucial role in stabilising the planet's tilt and climate. It is now agreed that the moon formed when the earth was struck by a Mars-sized body early in its history a freak occurrence. This suggests that any earth-like planets around other stars are likely to lack such a moon, and thus may not have stable enough climates to allow the evolution of advanced lifeforms. In expounding this "rare earth" theory, the authors draw on research from a number of diverse fields of study. As a result, their book provides a handy primer in astrobiology the emerging field that exists at the intersection between astronomy, biology and the planetary sciences. Many of the ingredients in the theory are not new. It has been suggested before, for example, that complex life on earth would never have evolved had it not been for the moon, or plate tectonics. But by stringing so many separate improbabilities together and by presenting each one in such detail, Mr Ward and Mr Brownlee make an extremely plausible case. As a final flourish, they add that, given the presumed rarity of complex life, it behoves man to take better care of the abundance of other species with which he shares the planet. The authors claim that they are voicing in "Rare Earth" a view privately held by many scientists looking for extraterrestrial intelligence. The earth's rarity would certainly explain why, despite all their efforts, no evidence for advanced extraterrestrials has been found so far. This carefully reasoned book makes a strong case for undoing at least some of the work of Copernicus, by accepting that the earth is special after all. It also makes the cosmos seem an even more vast and lonely place. __________ Exopolitics - Alternative News for ecology, consciousness & Universe politics. 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