[meteorite-list] NASA Study Suggest Giant Space Clouds Iced Earth

[Ron Baalke]

Gretchen Cook-Anderson
Headquarters, Washington                    March 3, 2005
(Phone: 202/358-0836)

John Bluck 
Ames Research Center, Moffett Field, Calif.
(Phone: 650/604-5026/9000)

Jim Scott
University of Colorado, Boulder
(Phone: 303/492-3114)

RELEASE: 05-066

NASA STUDY SUGGESTS GIANT SPACE CLOUDS ICED EARTH

Eons ago, giant clouds in space may have led to global 
extinctions, according to two recent technical papers 
supported by NASA's Astrobiology Institute.

One paper outlines a rare scenario in which Earth iced 
over during snowball glaciations, after the solar system 
passed through dense space clouds. In a more likely 
scenario, less dense giant molecular clouds may have 
enabled charged particles to enter Earth's atmosphere, 
leading to destruction of much of the planet's protective 
ozone layer. This resulted in global extinctions, 
according to the second paper. Both recently appeared in 
the Geophysical Research Letters.

"Computer models show dramatic climate change can be 
caused by interstellar dust accumulating in Earth's 
atmosphere during the solar system's immersion into a 
dense space cloud," said Alex Pavlov, principal author 
of the two papers. He is a scientist at the University 
of Colorado, Boulder. The resulting dust layer hovering 
over the Earth would absorb and scatter solar radiation, 
yet allow heat to escape from the planet into space, 
causing runaway ice buildup and snowball glaciations.

"There are indications from 600 to 800 million years ago; 
at least two of four glaciations were snowball glaciations. 
The big mystery revolves around how they are triggered," 
Pavlov said. He concluded the snowball glaciations 
covered the entire Earth. 

Pavlov said this hypothesis has to be tested by geologists. 
They would look at Earth's rocks to find layers that relate 
to the snowball glaciations to assess whether uranium 235 is 
present in higher amounts. It cannot be produced naturally on 
Earth or in the solar system, but it is constantly produced 
in space clouds by exploding stars called supernovae.

Sudden, small changes in the uranium 235/238-ratio in rock 
layers would be proof interstellar material is present that 
originated from supernovae. Collisions of the solar system 
with dense space clouds are rare, but according to Pavlov's 
research, more frequent solar system collisions, with 
moderately dense space clouds, can be devastating. He 
outlined a complex series of events that would result in 
loss of much of Earth's protective ozone layer, if the solar 
system collided with a moderately dense space cloud.

The research outlined a scenario that begins as Earth passes 
through a moderately dense space cloud that cannot compress 
the outer edge of the sun's heliosphere into a region within 
the Earth's orbit. The heliosphere is the expanse that begins 
at the sun's surface and usually reaches far past the orbits 
of the planets. Because it remains beyond Earth's orbit, the 
heliosphere continues to deflect dust particles away from the 
planet.

However, because of the large flow of hydrogen from space 
clouds into the sun's heliosphere, the sun greatly increases 
its production of electrically charged cosmic rays from the 
hydrogen particles. This also increases the flow of cosmic 
rays towards Earth. Normally, Earth's magnetic field and 
ozone layer protect life from cosmic rays and the sun's 
dangerous ultraviolet radiation.

Moderately dense space clouds are huge, and the solar system 
could take as long as 500,000 years to cross one of them. 
Once in such a cloud, the Earth would be expected to undergo 
at least one magnetic reversal. During a reversal, electrically 
charged cosmic rays can enter Earth's atmosphere instead of 
being deflected by the planet's magnetic field.

Cosmic rays can fly into the atmosphere and break up nitrogen 
molecules to form nitrogen oxides. Nitrogen oxide catalysts 
would set off the destruction of as much as 40 percent of 
the protective ozone in the planet's upper atmosphere across 
the globe and destruction of about 80 percent of the ozone 
over the polar regions according to Pavlov.

For information about NASA and agency programs on the Internet, 
visit:

http://www.nasa.gov


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