Earth sows its seeds in space
Life could be leaking out all over the cosmos.
23 February 2004
PHILIP BALL

The Earth could be scattering the seeds of life throughout our Galaxy.
Microbes could ride on specks of dust, powered by the Sun's rays, says
William Napier, an astronomer at the Armagh Observatory in Northern Ireland.

Scientists have pondered whether life might ride between star systems ever
since the nineteenth century. Some think that a collision between a
life-bearing planet and another celestial body could scatter stones and
boulders into space carrying living organisms. These deep-frozen spores
could then make their way to other worlds - an idea called 'panspermia'.

But the chances are stacked against such an event. Spores would have to
survive the meteor impact and be thrown into space. The boulder would then
have to leave the solar system and land on another life-supporting planet.
It would have to get there quickly, too. The radiation streaming through
space will cook any organisms in space rocks. Typically, says Napier, "the
boulders will be sterile by the time they are ejected from the solar
system".

But microbes might survive if they can escape the Sun's gravity more
quickly. And that might happen, says Napier, if the rocks they sit on are
first ground to dust1.

The Earth and her sister planets travel through a cloud of grains called
zodiacal dust. This is the debris from collisions in the asteroid belt and
from the passage of comets.

This dust should sand-blast anything passing through it, says Napier. This
process could grind a one-metre boulder down in 20,000-200,000 years, he
estimates. If a comet breaks up, thickening the dust, as happens several
times each million years, the process could take as little as five
centuries.

Read the rest at Nature
http://www.nature.com/nsu/040216/040216-20.html

Posted by
Robert Karl Stonjek.
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