How high is the sky? Scientists have a pretty good handle on that one, what with their knowledge of the troposphere, stratosphere an the other "o-spheres." Now, thanks to new work, they are closing in on the other half of that age-old query: How deep is the ocean? The researchers report that the world's total ocean volume is less than the most recent estimates by a volume equivalent to about five times the Gulf of Mexico, or 500 times the Great Lakes. While that might seem a lot at first glance, it is only about 0.3% lower than the estimates of 30 years ago....