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Rare Earth
Review by KEVIN BALDEOSINGHTITLE: Rare Earth
AUTHORS: Peter D. Ward & Donald Brownlee
PUBLISHER: Copernicus. (January 2000)
SORRY, Star Trek fans. It seems that even if we develop the technology to boldly go where no man has gone before, there may not be anyone there to meet us.
That, at least, is the strong implication of Rare Earth, written by geologist Peter D. Ward and astronomer Donald Brownlee. They suggest that the Earth, with its cargo of advanced animals, may be “virtually unique in this quadrant of the galaxy—the most diverse planet in the nearest 10,000 light years”.
The obvious objection to this thesis is that it doesn’t make mathematical sense. There are billions of stars out there, and probably trillions of planets. Statistical probability alone suggests that there should therefore a few thousand, or even hundreds of thousands, of Earth-like planets and, concomitantly, complex life.
Unfortunately, probability isn’t enough to ensure complex, intelligent life.
The development of plants, animals and humans on Earth wasn’t due solely to chance because, once the initial conditions were laid down, certain biological laws ensured that evolution would occur. But those initial conditions, according to Ward and Brownlee, are themselves highly improbable.
This is just a short list of the factors a planet needs for complex life to evolve, and each one seems to be essential. The planet has to be the right distance from its star, particularly to allow water to form, and the star has to be the right mass so it exists long enough for life to evolve.
The planet itself must have a stable orbit and the right mass to retain an atmosphere and the atmosphere must have the right temperature, composition and pressure for complex life. The planet must have the right size ocean and a large moon at the right distance to stabilise its tilt, and the tilt has to be such that the seasons aren’t too severe.
The planet must have a giant neighbour like Jupiter, which acts as cosmic garbage-collector, preventing meteors and asteroids hitting the planet and extinguishing life. The very galaxy has to be the right type, having enough heavy elements, and the planet can’t be at the centre, edge or the halo of the galaxy.
I must confess: after reading this list, even I nearly began thinking that there had to be a Creator. But I soon recovered from this lapse into irrationality and realised that the anthropic principle applied equally to the Earth as it does to the universe: if the conditions weren’t exactly right for us to exist, we wouldn’t be here to ask how come the conditions are exactly right for us to exist.
Being scientists, Ward and Brownlee are careful to hedge their bets: “The great danger to our thesis is that it is a product of our lack of imagination. We assume in this book that animal life will somehow be Earth-like. We take the perhaps jingoistic stance that Earth-life is every-life, that lessons from Earth are not only guides, but rules. We assume that DNA is the only way, rather than only one way.”
Having said that, however, they then insist that they do not believe their thesis is wrong. And, even though they admit that many factors “are known only in the sketchiest details”, they yet say “it is our contention that any strong signal can be perceived only when sparse data are available”.
These kinds of statements invariably signal an agenda. In Ward’s and Brownlee’s case, this appears to be the politically correct ecological one:
“...if animals are as rare in the Universe as we suspect, it puts species extinction in a whole new light. Are we eliminating species not only from our planet but also from a quadrant of the galaxy as a whole?” they write.
In my layman’s opinion, Ward and Brownlee’s thesis is at base hollow for the simple reason that we know next to nothing about the laws governing planet formation. I am also not comfortable with the fact that the only biological authority they cite is Stephen J. Gould, who renowned evolutionary biologist John Maynard Smith has described as “a man whose ideas are so confused as to be hardly worth bothering with”.
It may be that Ward and Brownlee are quite right about the rarity of Planet Earth. But I wasn’t convinced by their argument that complex life is as rare as they believe (though it did seem likely that our species may be among the most advanced in the universe since conditions were too violent nearer the centre after the Big Bang for life to evolve). But it is a scientific axiom that, given sufficient time, even the highly improbable will happen. That, after all, is how we ourselves came to be.