Ronald Rago, age 11, of Wichita, Kansas, for his question:

 How high is the stratosphere?

Gases are more fluid than water, more restless and changeable than liquid and solid substances. The gases of the earth's atmosphere reach hundreds of miles above our heads, getting thinner as they go. At certain levels, they change in character. The densest, most turbulent layer is the troposphere that hugs close to the surface of the globe. Its upper boundary averages five miles above the poles and reaches up to 11 miles above the equator. At the top is a slim, calm layer called the tropopause. It marks the lower limit of the layer called the stratosphere.

The floor of the stratosphere, then, is from 10 to .11 miles above the earth at the tropics and about five miles above the polar regions of the global surface. The upper boundary of the stratosphere averages about 50 miles above the surface level all around the globe.