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The
Swede Svante Arrhenius suggested a century ago that life in the
form of spores could survive in space and be spread from one planetary system
to another. According to Arrhenius, spores escape by random movement from the
atmosphere of a planet, and are spread throughout interstellar space by the weak
but persistent radiation pressure exerted by starlight. In a variation on this
theme, others have suggested that the spores might be spread deliberately by
intelligent beings. This theory is called "directed panspermia."
The modern version
of the panspermia idea starts from observations of prebiotic chemicals in
interstellar clouds. It seems certain that some of these raw materials, such as
amino acids, fell on to the young Earth and kick-started life.
Some researchers,
notably the late Fred Hoyle and Chandra Wickramasinghe, have argued that not
just complex organic substances, but even complete living organisms, albeit
bacteria, might have evolved in space on the surface of dust grains, then been
carried down to Earth by an impacting comet. There is also the possibility of
"ballistic panspermia," when rocks from one planet are
blasted into space by impacts and travel to another planet. The discovery on
Earth of meteorites from Mars' surface means that we might even be descended
from Martian bugs.
by John Gribbin, 30-Second Theory
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