|
In
1974, astronomer Carl Sagan estimated that "a million
civilizations may exist in our Milky Way galaxy alone." This
estimate was based in part on the work of Sagan and fellow
astronomer Frank Drake using a scientific formula known as the
Drake Equation. This equation attempts to calculate how many
advanced civilizations may exist in our galaxy.
In
their new book "Rare Earth," professors Peter D. Ward
and Donald Brownlee challenge the results of Sagan and Drake and
the corresponding Principle of Mediocrity. The authors state that
"the Principle of Mediocrity – the idea that Earth is but
one of a myriad of like worlds harboring advanced life –
deserves a counterpoint. Hence our book." It is their
contention that intelligent, complex animal life, separate from
microscopic life, is a rare occurrence in our galaxy.
The
motive behind this question has been attributed in part to the
rise of a new revolution in scientific investigation known as the
Astrobiology Revolution of the 1990s. The authors define the field
of astrobiology as "the field of biology ratcheted up to
encompass not just life on Earth but also life beyond Earth."
The success of astrobiology lies in its ability to think of entire
planets as ecological systems by embracing other disciplines such
as astronomy, oceanography, microbiology and geology.
Astrobiology
received a jump-start in the 1980s with the discoveries on Earth
of life existing in extreme environments of heat and/or pressure.
As a result of these discoveries, one question asked was, if life
can survive here under such conditions, why not on other planets
where similar conditions exist?
The
authors respond that "just knowing that life can stand
extreme environmental conditions is not enough to convince us that
life is actually there. Not only must life be able to live in the
harshness of a Mars or Venus, it must also have been able either
to originate there or to travel there." For these conditions
to exist, the authors argue, they should follow certain conditions
found on our own planet’s history – the energy output of the
orbiting star and its distance from the planet, the planet’s
size and chemical composition, a low asteroid/comet impact rate,
an orbiting moon of appreciable size to the host planet, the
placement of the planet in its host galaxy, and the planet’s
history.
(To
top of second column)
|
These
conditions present for the propagation of animal life are further
discussed in chapters entitled "Building a Habitable
Earth," "How to Build Animals," and "Mass
Extinctions and the Rare Earth Hypothesis." Even the geologic
phenomenon of continental drift is examined as an influence for
promoting complex life, since Earth is the only planet in our solar
system in which plate tectonics occur.
After
describing the circumstances that led to this explosion of life,
Ward and Brownlee bring their conclusions together in the chapter
"Assessing the Odds." Through critical analysis of the
different assumptions needed to complete the Drake Equation, the
authors have presented their own equation. The Rare Earth Equation
adds additional conditions and elements to the formula that were
discussed in the book’s earlier chapters. The result? "As any
term in such an equation approaches zero, so too does the final
product… to us, the signal is so strong that even at this time, it
appears that Earth indeed may be extraordinarily rare."
"Rare
Earth" is one of the most interesting science books to be
published in many years. This challenging work will appeal to
readers who wish to learn more about the possibility of complex life
outside of our own planet.
The
book is complemented by an outstanding set of tools: a scholarly
list of references used by the authors, a comprehensive index, and
useful charts on the dead zones of the universe (areas where
intelligent animal life could not exist) and the Rare Earth factors
(the conditions under which animal life formed on our planet).
This
book is highly recommended for all adult and young adult readers,
particularly those readers who enjoy the process of scientific
investigation.
For
more information, visit the library at 725 Pekin St. or call
732-8878.
[Richard
Sumrall, Lincoln Public Library District]
|
