- Hardcover: 338 pages
- Publisher: Copernicus; 2000 edition (January 14, 2000)
- Language: English
- ISBN-10: 0387987010
- ISBN-13: 978-0387987019
- Product Dimensions: 9.6 x 6.4 x 1.3 inches
- Shipping Weight: 1.6 pounds
- Average Customer Review: 180 customer reviews
- Amazon Best Sellers Rank: #553,286 in Books (See Top 100 in Books)
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Rare Earth: Why Complex Life is Uncommon in the Universe 2000th Edition
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"Do you feel lucky? Well do ya?" asked Dirty Harry. Paleontologist Peter Ward and astronomer Donald Brownlee think all of us should feel lucky. Their rare Earth hypothesis predicts that while simple, microbial life will be very widespread in the universe, complex animal or plant life will be extremely rare. Ward and Brownlee admit that "It is very difficult to do statistics with an N of 1. But in our defense, we have staked out a position rarely articulated but increasingly accepted by many astrobiologists."
Their new science
is the field of biology ratcheted up to encompass not just life on Earth but also life beyond Earth. It forces us to reconsider the life of our planet as but a single example of how life might work, rather than as the only example.
The revolution in astrobiology during the 1990s was twofold. First, scientists grew to appreciate how incredibly robust microbial life can be, found in the superheated water of deep-sea vents, pools of acid, or even within the crust of the Earth itself. The chance of finding such simple life on other bodies in our solar system has never seemed more realistic. But second, scientists have begun to appreciate how many unusual factors have cooperated to make Earth a congenial home for animal life: Jupiter's stable orbit, the presence of the Moon, plate tectonics, just the right amount of water, the right position in the right sort of galaxy. Ward and Brownlee make a convincing if depressing case for their hypothesis, undermining the principle of mediocrity (or, "Earth isn't all that special") that has ruled astronomy since Copernicus. --Mary Ellen Curtin
From Library Journal
Renowned paleontologist Ward (Univ. of Washington), who has authored numerous books and articles, and Brownlee, a noted astronomer who has also researched extraterrestrial materials, combine their interests, research, and collaborative thoughts to present a startling new hypothesis: bacterial life forms may be in many galaxies, but complex life forms, like those that have evolved on Earth, are rare in the universe. Ward and Brownlee attribute Earth's evolutionary achievements to the following critical factors: our optimal distance from the sun, the positive effects of the moon's gravity on our climate, plate tectonics and continental drift, the right types of metals and elements, ample liquid water, maintainance of the correct amount of internal heat to keep surface temperatures within a habitable range, and a gaseous planet the size of Jupiter to shield Earth from catastrophic meteoric bombardment. Arguing that complex life is a rare event in the universe, this compelling book magnifies the significanceAand tragedyAof species extinction. Highly recommended for all public and academic libraries.AGloria Maxwell, Penn Valley Community Coll. Lib., Kansas City
Copyright 1999 Reed Business Information, Inc.
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We know that every day new planets are being discovered and many of them exist in the habitable zone of their star. Some of these planets may, indeed, contain simple forms of life. However, according to the author/scientists, a planet requires a precise set of unique circumstances to allow for the long-term and varied evolution needed for the development of intelligent life. The reason for this conclusion are too numerous to explain in a review, but as the authors patiently explain the creation and formation of the Earth and the evolution of life on it, they make it very clear how unbelievably special the Earth is with respect to other planets and why conditions here are so rarely conducive to the steady evolution from single-celled organisms into intelligent life. If they are correct, and following their careful and detailed reasoning I believe their conclusions are logical, then one must appreciate the importance of protecting our unique, precious planet and wonder about the likelihood that we are the only significant form of life within hundreds of thousands [maybe millions] of light years.
If religion does not create of sense of respect for the dignity of other humans and our planetary home, this book certainly will. For example, five thousand years ago we believed the Earth was at the center of the universe. Then we learned that we orbit an average star. We later discovered that we reside at the outer edge of a galaxy in a universe that is populated with countless billions of galaxies. But, it is now possible that we will once again see ourselves as occupying one of the most special places within the entire universe.
The two authors are not the only scientists fostering this theory and I wish more was being written about it.
They wrote in the Preface to this 2000 book, "This book was born during a lunchtime conversation at the University of Washington faculty club, and then it simply took off. It was stimulated by a host of discoveries suggesting to us that complex life is less pervasive in the Universe than is now commonly assumed. In our discussions, it became clear that both of us believed such life is not widespread, and we decided to write a book explaining why... we have staked out a position rarely articulated by increasingly accepted by many astrobiologists... Perhaps in spite of all the unnumbered stars we are the only animals, or at least we number among a select few. What has been called the Principle of Mediocrity---the idea that the Earth is but one of a myriad of like worlds harboring advanced life---deserves a counterpoint. Hence our book."
In the Introduction, they explain, "In this book we will argue that not only intelligent life, but even the simplest of animal life, is exceedingly rare in our galaxy and in the Universe. We are not saying the LIFE is rare---only that ANIMAL life is. We believe that life in the form of microbes or their equivalents is very common in the universe... However, COMPLEX life---animals and higher plants---is likely to be far more rare than is commonly assumed. We combine these two predictions of the commonness of simple life and the rarity of complex life into what we will call the Rare Earth Hypothesis." (Pg. xiv) Later, they add, "To test the Rare Earth Hypothesis---the paradox that life may be nearly everywhere but complex life almost nowhere---may ultimately require travel to the distant stars." (Pg. xxi)
In the first chapter they observe, "The discovery that life is abundant and diverse in extreme environments is one of the most important of the Astrobiological Revolution. It gives us hope that microbial life may be present and even common elsewhere in the solar system and in our galaxy, for many environments on Earth that are now known to bear extremophile life are duplicated on other planets and moons of the solar system." (Pg. 3-4) Later, they add, "The discovery of extremophilic microbes has radically changed our conception of where life might be able to exist in the Universe---it causes us to reassess the concept of habitable zones. Scientists now realize that habitats suitable for MICROBIAL life are far more widely distributed in our solar system, and surely in the Universe as well, than was considered possible even in the most optimistic views... On the other hand, these same studies are showing that complex life... may have fewer suitable habitats than was previously thought. But just because life COULD exist in a place doesn't mean it is actually there. Life can be widely distributed in the Universe only if it can come into being easily." (Pg. 55-56)
They point out, "Most of the Universe is too cold, too hot, too dense, too vacuous, too dark, too bright, or not composed of the right elements to support life. Only planets and moons with solid surface materials provide plausible oases for life as we know it. And even among planets with surfaces, most are highly undesirable... of all yet KNOWN celestial bodies, earth is unique in both its physical properties and its proven ability to sustain life." (Pg. 35)
They state, "The lesson of Earth's Cambrian Explosion is that two parallel preparatory steps must be taken if complex metazoans¬--animals---are to appear. First, the oxygen atmosphere must be constructed... Second, a very large number of evolutionary adaptations must be concluded to allow the evolution of ... our animals---from the ... bacteria---that began it all. Both of these parallel tracks require time. There do not appear to be any shortcuts. On Earth, one or both required several billion years. And during that time, Earth had to maintain a temperature that allowed the presence of liquid water and avoid what we might call `planetary disasters' of sufficient magnitude to sterilize the evolving foot stocks of animals." (Pg. 156)
They observe, "We can summarize the implications of Earth's history of mass extinctions with regard to the Rare Earth Hypothesis as follows. Mass extinctions probably occurred rarely during the long period in Earth history when life was only of a bacterial grade. With the evolution of more complex creatures, such as eukaryotic cells, however, susceptibility to extinction increased.... As more and more species evolved within the various body plans, susceptibility to extinction decreased again. On any planet, the number of mass extinctions may be one of the most important determinants of where animal life arises and, if so, how long it lasts... inhabiting a cosmic neighborhood where large amounts of celestial collisions, supernovae, gamma ray bursts, or other cosmic catastrophes occur will also reduce a planet's likelihood of attaining and maintaining animal life." (Pg. 189)
They suggest, "It may be that plate tectonics is the central requirement for life on a planet and that it is necessary for keeping a world supplied with water. How rare is plate tectonics? We know that of all the planets and moons in our solar system, plate tectonics is found only on Earth. But might it not be even rarer than that? One possibility is that Earth has plate tectonics because of another uncommon attribute of our planet: the presence of a large companion moon..." (Pg. 220) They add, "Without the large moon, Earth would have had a very unstable atmosphere, and it seems most unlikely that life could have progressed as successfully as it has... Unfortunately, there is no evidence on how common large moons are for warm terrestrial planets close to their parent stars. We just don't know, and we probably won't for some time." (Pg. 234)
They summarize, "The Rare Earth Hypothesis is the unproven supposition that although microscopic, sludge-like organisms might be relatively common in planetary systems, the evolution and long-term survival of larger, more complex, and even intelligent organisms are very rare. The observations on which this hypothesis is based are as follows: (1) Microbial life existed as soon as Earth's environment made it possible, and this nearly invincible form of life flourished over most of Earth history... (2) The existence of larger and more complex life occurred only late in Earth history, it occurred only in restricted environments, and the evolution and survival of this more fragile variant of terrestrial life seem to require a highly fortuitous set of circumstances that could not be expected to exist commonly on other planets." (Pg. 243)
They acknowledge, "It is still impossible to observe smaller, rocky planets orbiting other stars. Perhaps such planets... are quite common. But ... We have hypothesized that animal life cannot long exist on a planet unless there is a giant, Jupiter-like planet with the same planetary system---and orbiting outside the rocky planets---to protect against comet impacts... To date, all tend to be in orbital positions that would be lethal, rather than beneficial, to any smaller rocky planets." (Pg. 269)
They also admits, "We assume in this book that animal life will be somehow Earth-like. We take the perhaps jingoistic stance that Earth-life is every-life, that lessons from Earth are not only guides but also RULES. We assume that DNA is the only way, rather than only one way. Perhaps complex life... is as widely distributed as bacterial life and as variable in its makeup. Perhaps Earth is not rare at all but is simply one variant in a nearly infinite assemblage of planets with life. Yet we do not believe this, for these is so much evidence and inference... that such is not the case." (Pg. 282)
This is a provocative, challenging, and intellectually stimulating book, that will be of great interest to anyone seriously studying cosmology, exobiology, life on other planets, and related topics.
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