Re: Did comets bring all the water to Earth?

It's unlikely that all of Earth's water was brought by comets, but not 
impossible.  You know how much water Earth has (about 4 quadrillion 
gallons), and that much water doesn't come in very quickly.  There would 
have had to have been a lot more comets with a lot more water in them 
during the time the Earth was forming, or whenever the water was brought, 
than now.  We don't really know how many comets were flying around that 
long ago.  I've never come across any of these authors that you mention, 
but I don't understand what they must mean.  No matter how hot the Earth 
is, if it has enough gravity, it can keep the water down- no matter what 
form it's in.  All forms of matter are equally affected by gravity.  The 
generally accepted idea is that it was originally gas, and then condensed 
into water when things cooled down.
Yes, there can not be water on a planet with no atmosphere.  The boiling 
point of a liquid is related to the pressure around it.  The higher the 
pressure around a liquid, the more energy is required in the liquid 
particles to escape the mass and become gaseous.  A liquid remains as such 
because the air pressure keeps it in place.  If no air pressure at all is 
present, then the particles immidiately escape.  All liquids boil in a 
vacuumm.