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Location: UFOUpDatesList.Com > 2007 > Apr > Apr 23

Ancient Mass Extinctions Caused by Cosmic Radiation

From: UFO UpDates - Toronto <ufoupdates.nul>
Date: Mon, 23 Apr 2007 07:20:46 -0400
Fwd Date: Mon, 23 Apr 2007 07:20:46 -0400
Subject: Ancient Mass Extinctions Caused by Cosmic Radiation

Source: National Geographic - Washington, DC, USA


April 20, 2007

[Links at site]

Ancient Mass Extinctions Caused by Cosmic Radiation, Scientists Say
Scott Norris
for National Geographic News

Cosmic rays produced at the edge of our galaxy have devastated
life on Earth every 62 million years, researchers say.

The finding suggests that biodiversity has been strongly
influenced by the motion of the solar system through the Milky
Way and of the galaxy's movement through intergalactic space.

Mikhail Medvedev and Adrian Melott, both of the University of
Kansas, presented their new theory at a meeting of the American
Physical Society earlier this month.

The theory offers the first explanation for a mysterious pattern
previously noted in the fossil record.

"There are 62-million-year ups and downs in the number of marine
animals over the last 550 million years," Melott said.

Until now, however, even the scientists who first discovered the
cyclical pattern had not been able to explain it. (Read related
story: "Mystery Undersea Extinction Cycle Discovered" [March 9,

A number of possible explanations had been considered=97including
volcanic activity, comet impacts, and changes in sea level=97but
none could account for the phenomenon's regularity.

The Kansas researchers discovered that high rates of extinction
in the cycle coincide almost perfectly with periodic
"excursions" of the solar system outside the central plane of
the Milky Way galaxy.

"Excursions to galactic north coincide with drops in
biodiversity," Melott said.

During these periods, which include some of the largest mass
extinctions known from the fossil record, Earth is bombarded
with high levels of cosmic radiation.

The radiation may harm biodiversity by causing mutations or by
triggering climate change, the researchers said.

Richard Muller is the University of California, Berkeley,
physicist who first discovered the 62-million-year cycle with
his graduate student Robert Rohde.

"We spent a year searching for possible mechanisms," Muller said.

"I was stunned when I learned that Medvedev and Melott had
succeeded where we had failed, and I congratulate them."

Cosmic Cause

Our solar system travels through the disk-shaped Milky Way on a
complicated circuit that takes about 225 million years to
complete. (See an interactive map of the solar system.)

At regular intervals, the system's wanderings take it up and
down through the thin central portion of the disk. The sun
reaches its farthest distance from the central plane every 62
million years.

The entire galactic disk, meanwhile, is hurtling through the hot
gas that surrounds it at about 125 miles (200 kilometers) a

"The movement [of the Milky Way] is not edge-on like a Frisbee,"
Melott noted. Instead, he said, it is flat, "like a pie in the

The new theory suggests that cosmic rays are continually
generated in a shock wave produced where the galaxy's "northern"
or forward side collides with surrounding gases.

As the solar system rises above the central plane it sticks out
like a cherry on top of the flying galactic pie=97closer to the
source of the cosmic radiation.

"We're exposed to the shock front more when we're emerging on
the north side of the galactic disk," Melott said.

At the same time, he explained, the solar system receives less
protection from powerful magnetic fields that form a shield from
cosmic radiation in the dense, central portion of the galaxy.

Impacts on Earth

Melott said his group applied their model to the largest
existing fossil database, which reconfirmed the finding of a 62-
million-year fluctuation in diversity.

In a paper recently accepted by Astrophysical Journal, the
Kansas researchers discuss various possible mechanisms by which
cosmic-ray exposure could result in mass extinctions.

One possibility is that organisms receive harmful doses of
radiation from high-energy particles known as muons, which are
produced by cosmic rays colliding with Earth's atmosphere.

"Cosmic rays themselves are not really that dangerous," said
Medvedev. "They create [charged particles] that propagate down
through the atmosphere=97especially muons that can go below the
sea level."

Changes in the chemistry of the atmosphere, and accompanying
depletion of the ozone layer, may also cause increased
mutations, he added.

In addition, charged particles produced by cosmic-ray
bombardment may cause greatly increased cloud cover, leading to
climate change.

The researchers said their model does not explain all major mass

For example the demise of the dinosaurs, which is thought to
have been caused by an asteroid impact, does not fit the 62-
million-year cycle. (Read related story: "'Dinosaur-Killer'
Asteroid Crater Imaged for First Time" [March 7, 2003].)

As for what lies ahead, the news is mixed. The solar system has
recently passed the galactic mid-plane and is on its way up,
Melott said, which could mean greater exposure to radiation.

But, he added, "the next cosmic ray effect is about ten million
years ahead of us."

[Thanks to 'The Norm' for the lead]

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