Assuming you mean "the depth of this water, if confined to a cross-sectional area the size of the United States", this is one of those nice Fermi estimation problems:
- I know the US contains hundreds of millions of people, and the world contains a single-digit number of billions. So the US has about 10% of the world's people.
- The US probably isn't particularly dense or sparse relative to other populated areas, so 1/10 the population should be 1/10 the Earth's land area.
- The Earth has twice as much ocean as land, and
- The ocean is a few miles deep - let's say 5 - so there's about 10 miles of ocean depth per land area.
- So compressing that to 1/10th the land area suggests the oceans should cover the US to a depth of about 100 miles.
The exact answer, it turns out, is about 89 miles - really close, without looking up a single piece of information!
I believe the US has about 350 million people out of about 7 billion people on Earth. That makes the US population equal to about 5% of the total, not 10%.
I'm trying to visualize the amount of water here, but it's hopeless unless an elementary student can calculate how many oil drums it would fill or football fields it would cover to a depth of one yard.
