Atmospheric Thickness

The atmosphere extends out from the earth 600 miles or more, if you consider every single stray molecule at the upper extents. A textbook that I have says, though, that 99% of the air in the atmosphere is contained within the first 30 kilometers (18 miles). If the earth was reduced to the size of an apple, 3 inches in diameter, how thick would this 18 mile layer be?

Answer:

Answer: About 2/3 of a hundredth of an inch.

Calculation: the radius of the earth is 4000 miles. Therefore, 4000 is to 18 as 1 1/2 inches is to the number of inches we are looking for. Therefore x = (18/4000) 1.5 inches = .00675 inches. This would be roughly as thick as a sheet of paper, or perhaps about the thickness of the peeling. (I will leave it to you to try to measure the thickness of an apple peeling.)