[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Impacts and ETs
One reason for the rare Earth notion is the supposed
need for a stabilizing moon. Dinosaurian history
suggests otherwise. During the Mesozoic, the whole
world was warm. Since solar declination had relatively
little effect on temperature, obliquity shifts
probably wouldn't have either.
I suggest we put off any conclusions regarding the
frequency of ET intelligence in the Galaxy until after
he Kepler and Terrestrial Planet Finder missions.
--- David Marjanovic <email@example.com> wrote:
> > Read paleontologist Peter Ward's book, "Rare
> Earth". Some of your
> > questions are addressed (although not necessarily
> answered) there.
> Peter D. Ward & Donald Brownlee: Rare Earth. Why
> Complex Life Is Uncommon in
> the Universe, Copernicus/Springer 2000
> Quotes from near the beginning...
> "Maybe we really are alone."
> "To put it another way, it is very difficult to do
> statistics with an _N_ of
> "Perhaps in spite of all the unnumbered stars, we
> are the only animals, or
> at least we number among a select few."
> "The idea of a million civilizations of intelligient
> creatures in our galaxy
> [Sagan, 1974] is a breathtaking concept. But is it
> credible? The solution to
> the Drake Equation includes hidden assumptions that
> need to be examined.
> Most important, it assumes that once life originates
> on a planet, it evolves
> toward ever higher complexity, culminating on many
> plaets in the development
> of culture. That is certainly what happened on our
> Earth. Life originated
> here about 4 billion years ago and then evolved from
> single-celled organisms
> to multicellular creatures with tissues and organs,
> climaxing in animals and
> higher plants. Is this particular history of life --
> one of increasing
> complexity to an animal grade of evolution -- an
> inevitable result of
> evolution, or even a common one? Might it, in fact,
> be a very rare result?
> 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 that _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, perhaps more common
> than even Drake and Sagan
> envisioned. 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."
> "What if the Earth, with its cargo of advanced
> animals, is virtually unique
> in this quadrant of the galaxy -- the most diverse
> planet, say, in the
> nearest 10,000 light-years? What if it is utterly
> unique: the only planet
> with animals in this galaxy or even in the visible
> Universe, a bastion of
> animals amid a sea of microbe-infested worlds?"
> Read the rest yourself. :-)
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around