The altitude of the upper boundary of the atmosphere
A)may be easily measured using a hot air balloon
B)may be easily measured using rockets
C)is difficult to determine because weather instruments don't work at high altitudes
D)is difficult to determine because we must first define how much air in a given volume indicates the presence of an atmosphere

Question

Quizplus · Accepted Answer

The altitude of the upper boundary of the atmosphere is difficult to determine because it requires a definition of what constitutes the presence of an atmosphere, such as how much air in a given volume is needed to say the atmosphere is present. This is more about defining a threshold rather than the technical limitations of measurement tools.

The Altitude of the Upper Boundary of the Atmosphere