Rating: 
Summary: Good arguments for why our Earth is rare
Review: This is a fascinating book. The authors address a fundamental question, "Are we alone in the universe?" They focus on various stages that other planets would have to go through to be like our Earth. They explain why each stage is very unlikely, and that this means our Earth is a very, very special place.
The Drake Equations, developed by Frank Drake, were an attempt to make an intelligent guess on the number of space going civilizations in our galaxy, and the whole universe. There were several factors, each having to do with a stage along the path to a space going civilization. Some scientists came up with a number like a couple million space going civilizations in our galaxy. The authors of "Rare Earth" believe that this is way too high. They break down the various factors of the Drake Equations and explain why it is unlikely to get through that stage successfully.
The authors make a large number of interesting observations. For example one of the things I found fascinating was in the last 500 million years there have been 15 mass extinctions of life on Earth. Another was just how important Jupiter being in a stable orbit has been in cleaning out random junk, thus reducing the amount of junk that could hit the Earth. Jupiter has probably cleared out 99.99% of the junk floating around our sun.
For me the most interesting thing was what the moon was doing to the Earth billions of years ago. Current models show some body of matter coming close to the Earth, losing its iron core to the Earth, and then some of the left over matter forming into the moon. It appears the moon originally may have been 15 times closer than it is now, so the gravity from the moon would have been 225 times greater. It appears this generated land tides in which the land on the Earth might be going up and down by hundreds of feet every couple hours, with the "waves" going thousands of miles per hour.
The book is full of many such interesting things. It is well written and I had a hard time putting it down. The authors comment on a large variety of topics relating to how unique our Earth may be. If you have any interest in this topic, this is a good book to read.
Rating: 
Summary: A Challenging Second Opinion
Review: +++++
This book, by Ward & Brownlee, considers if there are other extrasolar Earth-like planets (that is, Earth-like planets not of our sun). It is NOT saying that there are no extrasolar Earth-SIZE planets but only that extrasolar Earth-LIKE planets (that is, other planets that support carbon-based and DNA-based life as we know it) probably do not exist.
In other words, this book (and the authors state this) is using PROVEN forms of life known to exist which is the carbon-based and DNA-based life found on one planet known to have life -- Earth.
Also, this book is NOT saying that extrasolar planets that support life as we DO NOT know it (non-carbon based and non-DNA based life) do not exist. It's just that there is no hard evidence (but theoretically it's possible) for such life.
This book has a number of good features:
(1) REFERENCES. Over 25 pages that mainly consist of recent journal articles written by respected scientists.
(2) SUMMARY INTRODUCTIONS. There are two, 2-page summary introductions. They are entitled "Dead Zones of the Universe" (9 zones where life as we know it is thought not to exist) and "Rare Earth Factors" (18 factors that may be unique to Earth and that thus collectively permit life as we know it). These summary introductions provide a roadmap for the first 10 (of 13) chapters of this book.
(3) THE FIRST TEN CHAPTERS. These chapters are very detailed and build-up (using both historical theories and data as well as recent new theories and data) the summary information mentioned in (2) above.
(4) THE FINAL THREE CHAPTERS. These chapters are particularly interesting. Here we get more aquainted with Ward & Brownlee's Rare Earth Hypothesis (microbial life is common in the universe, but complex, multicellular life {such as human life} is rare) and introduced to the Rare Earth Equation. This hypothesis and equation are formulated from the information found in the first ten chapters mentioned in (3) above.
Despite these good features, there is one obvious distraction with this book -- it contains some factual errors. Here are just 4 examples: (1) some of the terms of the famous Drake Equation (developed by the SETI Institute's Dr. Frank Drake in 1961) are not correctly defined (2) the number of stars in our Galaxy is on average 200 billion (not million) (3) Mercury and Venus do not always present the same face to the sun (4) and the human genome has less than 100 thousand (not millions of) genes.
Normally, I would not nitpick like this but Ward & Brownlee are scientists and I feel that they should not have gotten these rather elementary facts wrong. However, it should be noted that these distractions do not undermine the main premise of the book.
Since this book is dedicated to the late Dr. Carl Sagan (as well as another person), I feel I should explain Sagan's results (presented in his best-seller "Cosmos") based on using the Drake equation that indicates another reason we may be alone, at least, in the Galaxy. Sagan calculates that "the number of [advanced technical] civilizations [known as "N"] in the Galaxy [could be] in the millions" (thus satisfying those who state the simple argument that since there's billions of stars in the Galaxy, there must be many advanced civilizations).
BUT Sagan also says that "The number N might be as small as 1 [just us]." Why does he say this? He explains: "If civilizations tend to destroy themselves soon after reaching a technological phase there might be no one for us to talk with but ourselves...Civilizations would take billions of years of tortuous evolution to arise [as Ward & Brownlee detail exquisitely], and then snuff themselves out in an instant [or some cosmic event snuffs them out as Ward & Brownlee again explain exquisitely]."
Finally, for an opposite opinion of what Ward & Brownlee's book present, I recommend Frank Drake's "Is Anyone Out There?: The Scientific Search for ExtraTerrestrial Intelligence" (paperback, 1994) and/or visting the SETI internet site.
In conclusion, despite some factual distractions, this book has a number of good features that collectively give a challenging second opinion regarding life in the universe. If you like challenges, then I strongly recommend that you read this book!!
**** 1/2
+++++
Rating:
Summary: A minor quibble - authors repeat Flat Earth Myth
Review: As a non-scientist, I found *Rare Earth* fascinating. I will leave it to scientists to debate the hypothesis, but I do have a minor quibble. The authors state: "During the Middle Ages, Earth was not only regarded as the center of the Universe but again was believed to be flat. St. Thomas Aquinas made Earth a sphere again but codified its place as the center of the Universe." Ward and Browlee probably learned this myth in grade school and since then never questioned it.
The truth is that in the Middle Ages all educated people (including Aquinas, of course) knew that Earth is a sphere. For example, the geography of Dante's *Divine Comedy* clearly assumes we are living on a globe. Also it should be noted that being at the center did not imply privilege. Satan was frozen at the very center of Dante's universe whereas the poet had to travel to the outer spheres of the heavens for the Beatific Vision of God. Perhaps astrobiologists like Ward & Brownlee will have the same experience!
Rating:
Summary: Gloomy picture for us Trekkies!!
Review: I both hate & love this book. I think it is a must read. Like all reviewers here, I am one of those who hopes that it's a "Star Trek" universe out there but unlike other reviewers on this board, I do not think that this book will get outdated anytime soon.This book without trying, seems to partially reconcile the `Creation' & `Evolution' hypothesis. It does this by sticking to the `Evolution' script but listing powerful arguments as to why `Life' as we know it may be unique or at least rare. In the face of mounting evidence, perhaps the church could support this hypothesis without losing legitimacy. The hypothesis is not built on one single argument & therein lies its strength. The book starts by making a clear distinction between microbial & animal life and concedes quickly that the former may be quite common around the universe. Animal life on the other hand, requires a fortuitous alignment of the stars and planets :) The first concept explored in this regard is that of a `Habitable Zone'(HZ). Off the 3 types of galaxies, only large spiral galaxies are likely to host life. The other two types are either too dense (globular galaxies) or too old (elliptical galaxies & small clusters), lacking the heavy elements necessary to sustain habitable conditions. The former is a problem of overcrowding, too much sun (literally), gravity, harmful radiation & frequent cataclysmic events (supernovae, black holes etc.). The latter would mean a world without a heated core, mostly composed of hydrogen & helium. Think of the Sun & Jupiter, what are the odds of life in these two places.
After eliminating all but spiral galaxies, the hypothesis also does the same to systems within spiral galaxies. Too close to the core and you have the same problems faced within globular galaxies, too far & you have the environment similar to an elliptical galaxy, i.e., too few heavy metals. That leaves only the arms of spiral galaxies as likely habitats for complex life. Within the HZ of galaxies, planets also have to be formed within the HZ of their star. Too close & they're toast (all water evaporates and escapes into space), too far and they are too cold to sustain anything but microbial life. Additionally it requires a star with certain properties, a certain size (only 5% of stars are the required size, most stars in the universe unlike our Sun are too small) and a high percentage of heavy metals (again a rare combination). Finally, the roles played by the Moon & Jupiter in supporting life on earth. The Moon stabilizes the rotation of the Earth. Imagine a basketball rolling on a floor rotating in varying directions as opposed to a top, rotating on a fixed axis. Without the Moon, the poles & equator would be constantly shifting. Our planet would be covered by water, temperatures & seasons would be unpredictable. Without Jupiter (because of its size & gravitational pull) attracting and capturing most celestial objects on a collision course with Earth, there would be many more large bodies crashing on earth and threatening life. You know what happened the last time this happened, ask Mr. T-Rex. Even assuming all these factors are duplicated, there is the additional factor of a time period. This ranges from the time the solar system has cooled down & the planets settled into stable orbits to the end when the star runs out of fuel & dies. Complex life has this time span to evolve, live & likely perish. The Rare Earth hypothesis is exactly that, it is not a law. Ward & Brownlee make a strong case, one whose implications I don't like but are nevertheless persuasive. If you are students of science, the origin and future of mankind, I would strongly recommend you read this book.
Rating: 
Summary: Interesting, but flawed hypothesis?
Review: I thoroughly enjoyed the book and the explanations given therein. My bone with the authors is that they have stretched their conclusions (namely that life in the Universe is a rare event) way too far. The idea that Earth is a perfect place for life because everything is 'just so' is not really new. Arguments for intelligent design (code-word for creationism) follow similar logic. The problem with the logic of this book is that it assumes all life must evolve exactly (or nearly so) as it did here on earth (same requirements, same molecular structure etc). Although this may be true, we simply do not yet know if that is the case. The authors do indeed argue that this is true only for complex life and therefore the discovery of simpler life forms may not negate their thesis. However, we also do not have enough information to make such a broad sweeping conclusion regarding the Universe. Ultimately, the argument comes down to what we observe in our own solar system and indeed we may be a 'rare earth' insofaras the type of complex life we have here, but complex life in other forms may be common elsewhere in the Universe. Indeed, the solar system may simply appear 'rare' because we are in charge of defining the term. Nevertheless, this is a very entertaining book and I encourage you to read it with a critical eye.
Rating: 
Summary: Not Up to Snuff
Review: OK, I am in the obvious minority with this review, but it's how I see it. This is a work filled with broad, sweeping suppositions, yet it seems that as always the devil is in the details and I was left unconvinced that the authors really had the details right to support their "Rare Earth" theory. It is an interesting, if ultimately unconvincing book. Interesting theory, lots of conjecture, and lots of "What if..." in every chapter. To me it seems that in many places sweeping statements are made, but never supported. Take for instance the statement on page 110 "Changes in ocean chemistry caused by increased tectonic activity beginning a billion years ago facilitated the evolution of skeletons." But the section does not, to me, provide adequate support or explanation for this supposition. Also take for example the Drake Equations which - while properly explained - is misstated in the details. The equation is usually written: N = R* x fp x ne x fl x fi x fc x L where: N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.
R* =The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
Ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space.
(Source: Seti Institute, http://www.seti-inst.edu/science/drake-bg.html) However, as given in the text of "Rare Earth" the formula is: N* x fs x fp x ne x fi x fc x fl = N This does not appear to be a big difference, however, the terms fi, fl, and fc are each mis-defined in the book. fi is defined as planets where life does arise, not intelligent life; fc as planets on which intelligent life emerges, not civilizations that develop a technology; and fl as percentage of lifetime of a planet that civilizations release detectable signals into space, not planets with life. This may seem nothing more then nit picking over details, but to me this is symptomatic of the entire work. If you can't even get a few simple 40 plus year old definitions right how accurate is the rest of the work? The belief that earth is the rarest of planets and then the selection of information to support that idea appears to be the main thrust here. Good science uses data to take you to a logical, fact supported conclusion, you get the reverse when to select facts to support a preconceived conclusion. Overall an unsatisfactory book.
Rating:
Summary: NASA Will Never Like This Book!
Review: Peter Ward and Donald Brownlee have written a very thought-provoking book in "Rare Earth." They have, in fact, given voice to some thoughts that had occurred to me and to a lot of others quite some time ago - namely "Where is everybody?" Flying saucer enthusiasts and alien abduction aficionados aside, most of us who think about such things have wondered why no alien civilization's radio transmissions have not obviously reached planet earth by now if alien civilizations were so common. Also we are starting to wonder where life exists in our solar system outside of Earth. When I was in my teens I eagerly kept track of every launch of a spacecraft. I dreamed of even becoming an astronomer specializing in planetary geology. But my true love was biology and the thought of a possible alien biological system was fascinating. I was soon disillusioned. First the veil of Venus was lifted and where swamps and dinosaur-like creatures roamed in science fiction was a barren acid and heat scorched version of Dante's Inferno. Mars was also found to be a volcanic version of the earth's moon, except with weather (dust storms mostly), pole caps of carbon dioxide and water ice, and a very thin atmosphere. The temperature of close to 100 degrees F. below zero did not seem promising and still does not. Thus the civilizations of Mars envisioned by Lowell disappeared into the Martian dust (as they had started to even before the first space probes). Then the moons Titan (Saturn) and Europa (Jupiter) were proposed as abodes of life, however weird, and a Martian meteorite with strange "nano-bacteria" was brought out. The latter "nano-bacteria" have become dubious at best and the moons are looking less promising by the day. Titan may have such a smoggy atmosphere and be so cold as to be certainly questionable as an abode for life. In addition to this, recent reports indicate that Europa is covered with a layer of concentrated sulfuric acid (possibly from the neighboring moon Io, which has sulfur volcanoes on its surface) and hydrogen peroxide- not exactly a good place for living things! To top it off some scientists think that the ice on Europa may actually cover a sea of sulfuric acid with a pH close to 0! If we cannot find even primitive living things (bacteria, lichens, fungi) on other planets in our system we may have to face the fact that life, while it may exist on numerous planets, is not nearly as common and as accessible as some would have it and that "civilizations" are even less common. Why is this? Ward and Brownlee have provided detailed answers, which, even if their formulae are somewhat flawed (as one reviewer suggested), are persuasive. We have to keep in mind that we do not know how long civilizations last or how often they occur but do not develop our type of technology. We are up against billion of years of time and trillions of cubic light years of space. Star Trek aside, we are not even sure that interstellar travel will ever be possible, so we may never know for sure what is out there. As Ward and Brownlee point out, to even have a planet with the possibility of life we have to have several conditions met. First planets revolving around multiple stars probably do not last long because of tidal effects and if they do life might have to cope with radical changes in surface temperature. Given that, we still have a number of candidate stars and have even found a number of such stars with planets (most of which are huge, some even by Jupiter standards). We also need planets within a star's habitable zone (assuming the star is not unstable and lasts long enough for the development of life). Then contingency has to allow for the development of living forms sometime during the life of the planet. To get more complex life than bacteria we need several billion years and perhaps a large moon. It gets even dicier if we want intelligent life, and even then we may have intelligent ocean-dwelling creatures who never develop radio and thus may not be detectable. Even if radio waves are produced by a civilization, we need to exist ourselves within that civilization's survival time frame (or actually light years later). Ward and Brownlee have provided, I think, some very good reasons why we are unlikely to find multicellular life on nearby planets or advanced technologies on planets even around distant stars. Even if life is fairly abundant in the universe (and I think it probably may be), planets with life (even at the bacterial level) may not be anywhere near as abundant as lifeless ones. This is not a reason to embrace creationism, as some would have it, but is simply a property of our universe. While I wish it were not so, I fear we cannot argue with the logic of this- especially with the little evidence we now possess. Of course one cannot completely rule out the possibility that Ward and Brownlee have missed something, but that is a present a meager hope. Read this book if you are interested in why complex life may be uncommon in the universe.
Rating:
Summary: "Rare Earth" Disappointments Aren't Rare Enough
Review: Rare Earth presents the interesting and not widely disseminated view that complex life forms are probably very rare in the universe. In other words, we haven't seen any ET's because there aren't any-or very few. The book makes this argument reasonably effectively and supports it with some science. I was disappointed that the science seemed pretty shallow-not really well done. There are just plain factual errors, e.g., the repeated assertion that Venus and Mercury present the same face towards the sun all the time, which leads to the elimination of a whole class of stars as potential homes for Earth type planets. Some science was confusingly presented, some just irrelevant, e.g., the discussion of periodite as distinct from basalt. One is tempted to dismiss these as minor flaws, but they are particularly irritating in light of the authors' hubris about our current knowledge. For instance, I think they too easily dismiss the possibility of complex life developing or surviving in some way we haven't thought of. Such a possibility could overcome the need for the presence or absence of certain chemicals, the necessity of protection from ultraviolet radiation, or relax temperature limits, etc. Another instance: in considering the consequences of the cessation of plate tectonics they predict, with no qualifications, that the continents will disappear, Earth will become a "waterworld", sea life will be aversely affected, carbon dioxide levels will drop to zero, the greenhouse effect will be diminished and Earth will freeze. There are no alternative hypothesis, no consideration of possible breaks in their chain of reasoning. The role of water vapor, clouds, the effects of increased areas of evaporation, the adaptability of life are not dealt with at all. This unqualified confidence seemed particularly unsuited to scientists who, as a group, find it necessary to change some aspects of their creation story every five months and can't come close to predicting next week's weather. The argument that the moon's role in stabilizing the obliquity of the Earth's spin axis was essential for the existence of long lasting complex life was unconvincing. It was hardly an argument, more just an assertion. I came away saying, "Maybe....but, well, maybe not." Another assertion, not even an argument, "the critical 40 degree C mark that is the upper temperature limit of animal life." Living in Phoenix Arizona, where the temperature reaches 50 degrees C, I'm tempted to say, "I don't think so." It was a little jarring to find several mentions of the current "mass extinction" mixed in with the statement, "The fossil record suggests that there are more species of animals and plants alive on Earth today than at any time in the past." No data is presented or alluded to; the nuances and profound uncertainties regarding the current stage of life on Earth are just not acknowledged-just boilerplate about rain forests and topsoil. The idea that intelligent life is very rare is important. This book presents that idea fairly well, but with some distressing and regrettable problems.
Rating:
Summary: Flawed but worth reading
Review: Rare Earth provides some fairly strong (and not well known) arguments that animal life on earth has been very lucky, and that planetary surfaces are typically much more hostile to multicellular life than our experience leads us to expect.
The most convincing parts of the book deal with geological and astronomical phenomena that suggest that earth-like conditions are unstable, and that it would have been normal for animal life to have been wiped out by disasters such as asteroids, extreme temperatures, supernovae, etc.
The parts of the book that deal with biology and evolution are disappointing. The "enigma" of the Cambrian explosion seems to have been explained by Andrew Parker (see his book In the Blink of an Eye) in a way that undercuts Rare Earth's use of it (dramatic changes of this nature seem very likely when eyes first evolve). This theory was apparently first published in a technical journal in 1998 (i.e. before Rare Earth).
They often assume that intelligence could only develop as it has in humans, even suggesting that it couldn't evolve in the ocean, which is rather odd given how close the octopus is to qualifying. But the various arguments in the book are independent enough that the weak parts don't have much affect on the rest of the arguments.
I was surprised that they never mentioned the Fermi Paradox, which I consider to be the strongest single argument for their position. Apparently they don't give it much thought because they don't expect technological growth to produce effects that encompass more than our planet and are visible at galactic distances.
Their concern over biodiversity seems rather misplaced. I can understand why people who overestimate mother nature's benevolence think that preserving the status quo is a safe strategy for humanity, but it seems to me that anyone sharing Rare Earth's belief that nature could wipe us out any time now should tend to prefer a strategy of putting more of our effort into creating technology that will allow us to survive natural disasters.
I am disappointed that they rarely attempt to quantify the range of probabilities they would consider reasonable for the risks they discuss.
Stephen Webb has written a book on roughly the same subject called Where is Everybody? that is more carefully argued, but less entertaining, than Rare Earth.
Rating:
Summary: We Might Be All Alone
Review: These two authors have written a highly informative book to support their thesis that we might well be the only multi-celled organisms in the universe. It should be stressed that Ward and Brownlee feel strongly that there are probably simple, bacteria like creatures on other planets, but nothing more complex. This is a most interesting book even if you do not agree with their hypotheses. It provides an entertaining and accessible summary of the biological, cosmological, and geological science involved in the development of our home planet. W&B feel that the necessary conditions for complex life are so numerous that few, if any, planets elsewhere could meet the requirements. Read this book and see: 1. Why the moon and Jupiter are essential for our existence. 2. Why a system of plate tectonics is vital for the development of life forms. 3. The effects that mass extinctions have had on evolution. 4. Why life may have originated in the deep ocean near hydrothermal vents. 5. Why earth is very lucky to be located on the far edge of our galaxy. For the scientific oriented layman this book is a true gem.
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