http://www.eco.freedom.org/el/20020802/reason.shtml
Are humans Gaia's immune system?
Defenders of the Earth
Book Review
By Ronald Bailey
The Gaia hypothesis, which holds that Earth is a living organism in its own
right, typically has been used to highlight man's role in messing up the
environment. But if the latest warning of a possible ecological catastrophe
turns out to be accurate, people could end up helping Gaia rather than
harming her.
The Gaia hypothesis--named after the Greek word for the Earth goddess, also
translated as "Earth Mother"--was devised in the 1970s by atmospheric
chemist James Lovelock and microbiologist Lynn Margulis. In
Gaia: A New Look
at Life on Earth, Lovelock and Margulis wrote, "The entire range of
living
matter on Earth from whales to viruses and from oaks to algae could be
regarded as constituting a single living entity capable of maintaining the
Earth's atmosphere to suit its overall needs and endowed with faculties and
powers far beyond those of its constituent parts." They said Gaia could be
defined as "a complex entity involving the Earth's biosphere, atmosphere,
oceans, and soil; the totality constituting a feedback of cybernetic systems
which seeks an optimal physical and chemical environment for life on this
planet."
Most evolutionary biologists reject the Gaia hypothesis as an unscientific,
although poetic, metaphor. But let's not let such quibbles trouble us today.
According to the Gaia hypothesis, the history of life on Earth can be
regarded as a progressive modification of the planet's chemistry and
temperature by biological organisms acting in ways that enhance their own
flourishing. For example, Earth's atmosphere was modified over billions of
years, by photosynthetic microorganisms, from one that was predominantly
carbon dioxide and methane, into its current oxygen-rich state. This
oxygen-rich atmosphere apparently set the stage for the evolution of
multicellular life that took off in earnest during the "Cambrian explosion"
some 540 million years ago.
In the millions of years following the Cambrian explosion, Gaia took out all
the stops, and the earth saw a vast diversification of life, and finally the
colonization of land by plants and animals. Then, 250 million years ago, the
Permian party came to a catastrophic end in which 95 percent of Earth's
species were wiped out. Gaia picked herself up and started over. Dinosaurs
and flowering plants eventually evolved to dominate the landscape in the
Cretaceous Period (146 to 65 million years ago). At the time, our tiny
mammalian ancestors were scrambling about the leaf litter, trying to avoid
becoming dinosaur snacks. The cornucopia of Cretaceous life came to an
abrupt end 65 million years ago, when 70 percent of all species became
extinct.
The leading explanation for these mass extinctions is the havoc caused by
asteroids slamming into the earth. The asteroid that brought the Cretaceous
Period to a close is thought to have been 10 miles wide, creating the
110-mile-diameter Chicxulub crater just off Mexico's Yucatan peninsula. The
massive Permian extinction is thought to have been caused by an asteroid 10
times bigger.
It's inevitable that Earth will be struck again. In 1908 a small comet or
asteroid, about 165 feet in diameter, exploded over the remote Tunguska
region of Siberia, releasing energy equivalent to 15 megatons of TNT, 1,000
times stronger than the atomic bomb dropped on Hiroshima. In 1989 an
asteroid measuring a quarter of a mile in diameter missed Earth by just
400,000 miles. In 1994 the house-sized asteroid XM1 was spotted only 14
hours before passing within 65,000 miles of Earth, well inside the moon's
orbit of 238,000 miles. In June an asteroid the size of a soccer field
missed Earth by 75,000 miles.
Scientists estimate that an asteroid with a diameter of a kilometer (0.62
mile) could destroy civilization by drastically changing the earth's climate
after impact, and kill one-quarter of the world's population. This disaster
scenario was popularized in 1998 by two mediocre movies, Deep Impact, and
Armageddon.
So far, astronomers have identified over 26,000 asteroids in our solar
system. The 1,700 or so that regularly pass close to Earth's orbit are
designated Near Earth Objects, or NEOs. Six hundred NEOs measure more than a
kilometer in diameter. The National Aeronautics and Space Administration's
Jet Propulsion Laboratory helpfully lists more than a score of upcoming near
misses for those who have a morbid interest in such things.
The latest scare occurred last week with the detection of asteroid 2002 NT7,
which measures more than a mile in diameter. Initial calculations showed
that there was a small probability that it might hit the earth on February
1, 2019. Fortunately, subsequent analysis found that civilization will be
spared until at least February 1, 2060, when there is a very tiny chance the
asteroid will hit us. In the meantime, NASA and the European Space Agency
are increasing their monitoring of NEOs and thinking of ways to deflect or
blow up any asteroids that threaten to smash into Earth.
What do asteroid impacts have to do with the Gaia hypothesis? In Gaia: A New
Look at Life on Earth, Lovelock asked, "To what extent is our collective
intelligence also a part of Gaia? Do we as a species constitute a Gaian
nervous system and a brain which can consciously anticipate environmental
changes?"
Perhaps Gaia has gotten tired of being whacked by asteroids and having to
restart biological evolution over and over again. Perhaps she evolved
technologically sophisticated, big-brained mammals who can travel in space
as a way of protecting herself from asteroids. Like antibodies that protect
the body from invading disease organisms, humans can defend our Earth Mother
against extraterrestrial intruders. Just a thought.
Ronald Bailey, Reason's science correspondent, is the editor of
Global
Warming and Other Eco Myths (Prima Publishing) and
Earth Report 2000:
Revisiting the True State of the Planet (McGraw-Hill).
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