Rare Earth: Why Complex Life Is Uncommon in the Universe

Rating:
Summary: Interesting, whether one agrees with it or not
Review: This book, which describes the development of intelligent life on Earth, is popular and well-written, with plenty of interesting references. And it attempts to defend a controversial thesis, namely that while life may be prevalent in the Universe, intelligent life is rare.

The claim that life itself is at least as common as many others suspect is based on the ability of many "extremophiles" (some of which may resemble the initial forms of life on Earth) to subsist well outside what many observers would previously have called a "habitable environment." The authors also note the fact that unicellular life on Earth appears to have arisen fairly quickly.

The claim that intelligent life is rare is based on the fact that multicellular animal life appears to require a large number of potentially difficult steps to evolve, and in fact took a relatively long time to develop on Earth. The authors argue that many aspects of the Earth's nature and history are relatively rare, and that these aspects significantly increased the chance that intelligent life would develop as fast as it did. In addition, the authors point out that the development of intelligent life requires being lucky at several key points. For example, intelligent life on Earth required an oxygen-rich atmosphere. This was provided by early unicellular life. But the production of oxygen wrecked much of the "greenhouse effect" that had made the Earth's surface relatively warm. The cooling of the Earth that resulted probably did not slow down the further evolution of life, if anything, the authors suspect that it speeded it up. But on other planets, such a reduction of temperature would have been more likely to destroy life than enhance it.

This is a very readable and interesting book, and I certainly recommend it.

Rating:
Summary: The Thesis That Spells Death For Modern Science Fiction
Review: This is one of the most astonishing books I have ever read. Its thesis, that complex life similar to life on the Earth, is probably very rare in the galaxy, if not the universe. The authors meticulously build a case for Earth's special place in the cosmos, showing how bacterial life might be common but that anything bigger than simple organisms might not be able to survive the ravages of time and comets and wandering axial tilt. As other readers have pointed out, this doesn't necessarily mean that silicon-based life or some other kind of life can't exist in the universe, but it does demonstrate that Fermi's Dilemma might in fact be true. As a science fiction writer, I was stunned at how much this book could change the way science fiction is written. No more Star Trek universes with complex life in every system, no more "federations" or "foundations" or "assemblies" of thousands of inhabited worlds. According to the thesis Ward and Brownlee present, habitable worlds might be few and far between. Humans may very well find no other worlds beyond the Earth upon which to live. RARE EARTH will make it difficult to read books or watch movies that envision a galaxy filled with wonderful and curious creatures, where humans spread out across the galaxy as if they were so many islands in Polynesia. And if the Rare Earth hypothesis is true, then we are also obliged to get our act together here and now if we are going to become a space-going species. I think this book puts a lot of science fiction writers out of business. It certainly makes a lot of science fiction, including my own, seem downright silly.

Rating:
Summary: A Great Entry In A Terrific Debate
Review: This is one side of a fascinating debate, between astrobiologists and xenobiologists. In Rare Earth, there is a detailed explanation of what there is about planet Earth that made life possible, and what might have induced divergence. Thus the question, "how lucky are you to be here" is answered in superb detail. In a contrasting book, "What Would A Martian Look Like?", one looks at the question of just how large is the solution space for life, or how many ways might life get going and develop. We might never really know which approach is correct, but I find the issue worthy of consideration.

Rating:
Summary: A Great Entry In A Terrific Debate
Review: This is one side of a fascinating debate, between astrobiologists and xenobiologists. In Rare Earth, there is a detailed explanation of what there is about planet Earth that made life possible, and what might have induced divergence. Thus the question, "how lucky are you to be here" is answered in superb detail. In a contrasting book, "What Would A Martian Look Like?", one looks at the question of just how large is the solution space for life, or how many ways might life get going and develop. We might never really know which approach is correct, but I find the issue worthy of consideration.

Rating:
Summary: Rare Earth Factors: Too Many Contingencies
Review: This is the best book I've seen so far in listing the contingencies for life to exist and evolve [quote]:

 Right distance from star
Habitat for complex life.
Liquid water near surface.
Far enough to avoid tidal lock.

 Right planetary mass
Retain atmosphere and ocean.
Enough heat for plate tectonics.
Solid/molten core.

 Plate tectonics
CO2-silicate thermostat.
Build up land mass.
Enjance biotic diversity.
Enable magnetic field.

 The right tilt
Seasons not too severe.

 Atmospheric properties
Maintenance of adequate temprature,
composition and pressure for plants
and animals.

 Right kind of galaxy
Enough heavy elements.
Not small, elliptical, or irregular.

 Right mass of star (sun)
Long enough lifetime.
Not too much ultraviolet.

 Jupiter-like neighbor
Clear out comets and asteroids.
Not too close, not too far.

 Ocean
Not too much.
Not too little.

 Giant impacts
Few giant impacts.
No global sterilizing impacts after an
initial period.

 Biological evolution
Successful evolutionary pathway to
complex plants and animals.

 Right position in galaxy
Not in center, edge or halo.

 Stable planetary orbits
Giant planets do not create chaos.

 A Mars
Small neighbor as possible life source
to seed earth-like planet, if needed.

 Large Moon
Right distance.
Stabilizes tilt.

 Right amount of carbon
Enough for life.
Not enough for Runaway greenhouse.

 Evolution of oxygen
Invention of photosynthesis. Not too
much or too little. Evolves at the right
time.

 Wild Cards
Snowball Earth. Cambrian explosion.
Inertial interchange event. [/quote]

Together with this helpful TIMELINE OF EVOLUTION:

4.5 Billion Years Ago: Earth formed
4 BYA: "Life" (bacteria/archaea)
1 BYA: Multicelluar algae and seaweed i.e., "complex life" took 3.5 billion years!
600 Million YA: Sponges/Worms
475 MYA Plants/Fungi
450-365 MYA Non-flying insects, arthropods and fish
300 MYA: Reptiles on land
250 MYA: Mass extinction wipes out 95% of animal species
220 MYA: First mammals
200 MYA: Birds
65 MYA: 50% of animal species die from meteor cooling planet
1800 Thousand YA: Homo erectus
130 TYA: Neanderthals (Homo Neanderthenis)
100 TYA: Homo sapiens "intelligent life"
30 TYA: Man migrates to North America
27 TYA: Neanderthals extinct
4 TYA: Humans record history

The Moral of the Story:

Love Life: Abolish Money, Law & State.