-Caveat Lector-
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From: [EMAIL PROTECTED]
Date: May 15, 2007 3:03:30 AM PDT
To: [EMAIL PROTECTED]
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Subject: Fwd: Out-of-This-World Hypothesis: Galactic Forces Control
Life on Earth
See what's free at AOL.com.
From: "Jim S." <[EMAIL PROTECTED]>
Date: May 14, 2007 7:21:53 PM PDT
To: undisclosed-recipients:;
Subject: Out-of-This-World Hypothesis: Cosmic Forces Control Life
on Earth
http://www.livescience.com/space/scienceastronomy/
070423_cosmic_evo.html
*Out-of-This-World Hypothesis: Cosmic Forces Control Life on Earth*
By Ker Than, Staff Writer
posted: 23 April 2007 07:54 a.m. ET
The rise and fall of species on Earth might be driven in part by
the undulating motions of our solar system as it travels through
the disk of the Milky Way, scientists say.
Two years ago, scientists at the University of California, Berkeley
found the marine fossil record shows that biodiversity -- the
number of different species alive on the planet -- increases and
decreases on a 62-million-year cycle. At least two of the Earth’s
great mass extinctions -- the Permian extinction 250 million years
ago and the Ordovician extinction about 450 million years ago --
correspond with peaks of this cycle, which can’t be explained by
evolutionary theory.
Now, a team of researchers at the University of Kansas (K.U.) have
come up with an out-of-this-world explanation. Their idea hinges
upon the fact that, appearances aside, stars are not fixed in
space. They move around, sometimes rushing headlong through
galaxies, or approaching close enough to one another for brief
cosmic trysts.
In particular, our Sun moves toward and away from the Milky Way’s
center, and also up and down through the galactic plane. One
complete up-and-down cycle takes 64 million years -- suspiciously
similar to Earth’s biodiversity cycle.
Galactic Bow Shock
The K.U. researchers independently confirmed the biodiversity cycle
and have proposed a novel mechanism by which the Sun’s galactic
travels is causing it.
Scientists know the Milky Way is being gravitationally pulled
toward a massive cluster of galaxies, called the Virgo Cluster,
located about 50 million light years away. Adrian Melott and his
colleague Mikhail Medvedev, both K.U. researchers, speculate that
as the Milky Way hurdles towards the Virgo Cluster, it generates a
so-called bow shock in front of it that is similar to the shock
wave created by a supersonic jet.
"Our solar system has a shock wave around it, and it produces a
good quantity of the cosmic rays that hit the Earth. Why shouldn’t
the galaxy have a shock wave, too?" Melott said.
The galactic bow shock is only present on the north side of the
Milky Way's galactic plane, because that is the side facing the
Virgo Cluster as it moves through space, and it would cause
superheated gas and cosmic rays to stream behind it, the
researchers say. Normally, our galaxy’s magnetic field shields our
solar system from this "galactic wind." But every 64 million
years, the solar system's cyclical travels take it above the
galactic plane.
“When we emerge out of the disk, we have less protection, so we
become exposed to many more cosmic rays,” Melott told SPACE.com.
How Cosmic Rays Affect Life
The boost in cosmic-ray exposure could have both a direct and
indirect effect on Earth’s organisms, said KU paleontologist Bruce
Lieberman. The radiation could lead to higher rates of genetic
mutations in organisms or interfere with their ability to repair
DNA damage, potentially leading to diseases like cancer.
Cosmic rays are also associated with increased cloud cover, which
could cool the planet by blocking out more of the Sun’s rays. They
also interact with molecules in the atmosphere to create nitrogen
oxide, a gas that eats away at our planet’s ozone layer, which
protects us from the Sun’s harmful ultraviolet rays.
Richard Muller, one of the UC Berkeley physicists who co-discovered
the cycle, said Melott and his colleagues have come up with a
plausible galactic explanation for the biodiversity cycle. Muller
and Robert Rohde also speculated that our solar system’s movement
through the galactic plane was behind the cycle, but the pair could
not conceive of any reason why conditions on the north and south
side of the galactic plane should differ.
"That's where they succeeded," Muller said in a telephone
interview. "They came up with something we didn’t think of, which
puts an asymmetry in. I’m delighted they did that and I
congratulate them."
A First-step Hypothesis
Richard Bambach, a paleontologist at the Smithsonian Museum of
Natural History who was not involved in the study, said he is
excited the biodiversity cycle has been independently confirmed,
but cautions the galactic hypothesis is still in the early stages
of formulation.
"It's a first-step hypothesis," Bambach said. "It's an interesting
idea, but we’re a long way from knowing if that is really why
biodiversity changes."
For one thing, scientists have yet to discover a bow shock around
the Milky Way, though such shock waves have been found around other
galaxies.
"I think it's a very nice idea," said Philip Appleton, a Caltech
astronomer. "I think we’re only beginning to come to grips with
these kinds of behaviors. We're realizing that not only do
galaxies interact with each other gravitationally, but also that
the environment they’re traveling through -- the ‘wind’ they create
-- can actually produce noticeable effects."
Last year, Appleton and his team discovered a bow shock surrounding
a galaxy in Stephan's Quintet, a galactic cluster located 300
million light years away. The shock wave is traveling about 620
miles (1,000 km) per second relative to the cluster.
The Milky Way is hurtling toward the Virgo Cluster at about 125
miles (200 km) per second, so any bow shock it generates would
consequently be weaker, Appleton said.
If future studies confirm the galaxy-biodiversity link, it would
force scientists to broaden their ideas about what can influence
life on Earth. "Maybe it’s not just the climate and the tectonic
events on Earth," Lieberman said. "Maybe we have to start thinking
more about the extraterrestrial environment as well."
"Moral progress has consisted in the main of protest against cruel
customs,
and of attempts to enlarge human sympathy."-- Bertrand Russell
Julienne's Blog:
www.myspace.com/youandthecosmos
- 5/10/07 How we let ourselves be fooled.
Radio: "You and the Cosmos" WHRWFM.org
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