View Single Post
Old 05-23-2009, 05:36 PM
Ximenean Ximenean is offline
Join Date: Aug 2001
Posts: 7,112
Originally Posted by Shalmanese View Post
The total volume of water on earth is 1 360 000 000 km≥ [1] which weighs 1.36*10^21kg [2]. The mass of the earth is 5.97*10^24 kg[3] so water makes up 0.23% [5].

A billiard ball weighs 150 grams [6] so 0.23% of that is 0.034 grams[7] which is roughly equivilant to:

~ 0.4 x typical large sand grain mass (~ 9x10^-5 kg )
~ 10 x mass of a typical snowflake (~ 3x10^-6 kg )
~ 20 x mass of a typical mosquito (~ 1x10^-6 kg )
Radius r of a drop of water from m=rho 4pir^3/3:
| 2 mm (millimeters)
| (assuming water density ~~ 1000 kg/m^3)

So no, I'm betting it wouldn't leave a wet trail. There's slightly less than a single drop of water on your earth billiard ball.
I think you're a factor of ten out there. I make it that water is 0.023% of the total mass of the Earth.

It is startling, how thin the layer of water on the Earth's surface is. For something that affects the climate and the biology so much to be little more than a film of water on the surface.

It always seems fortuitous to me that there is just the right amount of water on the Earth. Not enough to make the planet a Waterworld, but enough so that the place is not an arid desert punctuated by the occasional lake. Maybe it's an example of the anthropic principle. I doubt that desert planets have much going for them, but could civilisation have arisen on a planet entirely covered by water?
(Kevin Costner notwithstanding.)