Well, the comet theory isn't entirely dead. The Deep Impact project last summer proved that comets can contain immense amounts of water. It spouted water for days after the impact.
There was also (to the scientists' surprise) water ice on the surface:
http://www.nasa.gov/mission_pages/de...water_ice.html
A chief scientist said (early this year):
Quote:
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Originally Posted by Chief Scientist
"Understanding a comet’s water cycle and supply is critical to understanding these bodies as a system and as a possible source that delivered water to Earth," she said. "Add the large organic component in comets and you have two of the key ingredients for life."
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Which shows that the water-from-comets idea is far from passe, nor is the life-from-comets idea dead.
Edit: The "death-from-comets" theory is still alive, too.
I do agree with HydrogenBond that life may well have come about on Earth without the help of matter from comets. Some have speculated that comet impacts may have caused impact fragments to blast into space and carry life between the planets (ie, we could all be Martians
).
