Which layer is commonly described as the boundary between the atmosphere and space?

Which layer is commonly described as the boundary between the atmosphere and space?

• A. Ionosphere
• B. Thermosphere
• C. Mesosphere
• D. Exosphere

Answer: (D)

The boundary between Earth’s atmosphere and space is defined by the exosphere, the outermost layer of the atmosphere. In this region the air is incredibly thin and particles are far apart, so molecules can escape into space and the atmosphere gradually fades into the vacuum of space. The exosphere marks the transition from a planetary atmosphere to interplanetary space, more so than the other layers. The thermosphere and mesosphere are still considered part of the atmosphere, while the ionosphere is a layer within the upper atmosphere that is ionized and overlaps with these regions, but it isn’t the boundary itself. The exosphere typically begins hundreds of kilometers above Earth and extends outward, merging with space.

The boundary between Earth’s atmosphere and space is defined by the exosphere, the outermost layer of the atmosphere. In this region the air is incredibly thin and particles are far apart, so molecules can escape into space and the atmosphere gradually fades into the vacuum of space. The exosphere marks the transition from a planetary atmosphere to interplanetary space, more so than the other layers. The thermosphere and mesosphere are still considered part of the atmosphere, while the ionosphere is a layer within the upper atmosphere that is ionized and overlaps with these regions, but it isn’t the boundary itself. The exosphere typically begins hundreds of kilometers above Earth and extends outward, merging with space.