AND ASTEROIDS CAN HAVE POSITIVE ECOLOGICAL EFFECTS
by Whit Gibbons
May 1, 2005
for something completely different. A recent scientific paper heralds
potential ecological benefits that can result from enormous comets or
asteroids striking Earth. Understanding, of course, that whatever or whoever
happens to be at the point of contact when a sizable rock knocks a half-mile-diameter
crater in the earth’s surface will find little positive to report.
In fact, they will not be around to report at all. Nonetheless, according
to the authors, the impacts of asteroids and comets “can also have
beneficial influence on processes from the molecular to the evolutionary
for the journal “Trends in Ecology and Evolution,” the paper
by Charles S. Cockell of the Open University in England and Philip A.
Bland of Imperial College London gives an intriguing perspective and positive
spin to what many would consider the world’s worst nightmare. But
what happens to life on a global scale must be viewed differently from
what happens to a particular species or region at ground zero. Hence,
these “extraterrestrial agents of biological change” can be
credited with contributing to important steps in the process of life on
First, making a distinction between the world colliding with a meteor
that is a comet, which is made up of frozen gasses and rocks, and one
that is an asteroid, which is almost all rock, is unnecessary for making
the point that a sizable chunk of either would get our attention if it
made it through Earth’s atmosphere to the ground. By one calculation,
collision with a rock six miles in diameter would release an unimaginable
explosion--“the equivalent energy of 10 million megatons of TNT”;
1,000 times more powerful than the atomic bombs dropped on Japan to end
World War II. Whether the impact was made by rocks from a comet or an
asteroid wouldn’t much matter.
to the article, past collisions could have resulted in at least three
notable outcomes for life on Earth. First, and most important if true,
is that extraterrestrial impacts could have prestaged the beginning of
life. The prelife scenario could have been one in which a meteor actually
brought the organic materials necessary for the chemical reactions that
eventually led to living matter. Another hypothesis is that the impact
provided a dramatic jolt of energy that led to the development of complex
molecular structures necessary for life. Even a significant portion of
the life-essential water present on Earth today could have arrived in
the form of ice-laden comets that melted upon impact. All of this would
have happened about 4 billion years ago, give or take a decade or two,
so it all is obviously theory, not fact. But providing alternative hypotheses,
when no one knows for sure, is what science is all about.
beneficial feature of celestial bombardment would have occurred after
life on Earth was already well established. Most meteors hitting Earth
today land in the oceans, which cover three-fourths of the planet. One
paleontological record in the Arctic Ocean suggests that an enormous tsunami
was created from an impact several million years ago. Sediments today
indicate that the inland wave was of such proportion that high productivity
was created by the distribution of water inland that brought nutrients
back to the sea. Impacts on land itself create craters that can become
freshwater lakes that support life forms incompatible with marine environments.
Such reorganization of hydrological and nutrient cycles, as well as the
creation of new habitats, can be viewed as beneficial to life on Earth
in the broadest sense.
the paper presents the positive side of the extinction of entire groups
of organisms as a consequence of massive meteor collisions. For example,
200 million years ago a collision of such proportion occurred that much
of life on Earth was diminished due to darkened skies, acid rain, flooding,
and fires. Following this event, the dinosaurs evolved and became the
reigning animals until 65 million years ago when it happened again. Following
that event came the mammals and us.
not stay up nights worrying about the phenomenon reoccurring, as impacts
of such magnitude occur only about once every 100 million years or so.
With 35 million years to go, it's a bit early to start counting.
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