Layers of the atmosphere

Correct answer: A. Polar regions receive less solar heating, so their lower atmosphere is generally colder and has weaker vertical convection. The troposphere is therefore generally thinner over the poles, placing its upper boundary, the tropopause, at a lower altitude than in the tropics.

Correct answer: D. The troposphere is the lowest major atmospheric layer, with the stratosphere directly above it. Their boundary is called the tropopause. The stratopause is instead the upper boundary of the stratosphere.

Correct answer: A. The stratosphere is relatively stable, so vertical mixing is limited. In much of this layer, temperature increases with height, which discourages strong upward convection. This is one reason storms and other weather disturbances are much less common there than in the troposphere.

B is correct. Stratospheric ozone absorbs much of the Sun's harmful ultraviolet radiation before it reaches Earth's surface. This reduces the amount of UV radiation reaching living organisms. Ozone does not form soil, remove salt from oceans, or prevent earthquakes.

Correct answer: C, the stratosphere. The ozone-rich region called the ozonosphere is located mainly in the stratosphere, where ozone absorbs much of the Sun’s harmful ultraviolet radiation.

Correct answer: A, the stratosphere. The stratopause is the boundary at the top of the stratosphere, where it meets the mesosphere. The troposphere’s upper boundary is called the tropopause.

Correct answer: B, the stratosphere. From Earth upward, the main atmospheric layers are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Therefore, the mesosphere lies directly above the stratosphere.

B is correct. A meteoroid entering the atmosphere at very high speed collides with air molecules and compresses the air in front of it. These processes heat the meteoroid and surrounding gas, making the meteor glow; the object may also ablate. Water-vapour condensation, ocean waves, and soil pressure do not cause this heating.

C is correct. The mesopause is the upper boundary of the mesosphere; the thermosphere begins above it. The names of the other layers’ upper boundaries are tropopause and stratopause.

D is correct. Temperature generally falls through the mesosphere and reaches its lowest atmospheric values near the mesopause, the boundary between the mesosphere and thermosphere.

A is correct. From lower to higher altitude, the main layers are troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Thus, the thermosphere lies directly above the mesosphere.

B is correct. In the ionosphere, energetic solar radiation can remove electrons from some atoms or molecules, producing positively charged ions and free electrons. Not every particle is ionized at all times, but charged particles are a defining feature of this region.

C is correct. The ionosphere contains ions and free electrons that can bend or reflect some radio frequencies back toward Earth. This can let some radio signals reach beyond the normal line-of-sight horizon. The effect depends on the radio frequency and ionospheric conditions.

Correct answer: A. From Earth’s surface upward, the atmospheric layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Option A gives this order; option D gives it in reverse.

Correct answer: B. From bottom to top, the layers are troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Reversing that order gives exosphere, thermosphere, mesosphere, stratosphere, and troposphere from top to bottom, as shown in B.

The correct answer is A, the troposphere. It contains most of the atmosphere’s water vapour, and air movement within this lowest major layer helps clouds form and produces most rainfall and other ordinary weather.

The correct answer is B, the ozone layer in the stratosphere. Ozone absorbs much of the Sun’s harmful ultraviolet radiation before it reaches Earth’s surface. The other listed features do not provide this protection.

The correct answer is C, the mesosphere. Many meteors become visible as they heat up while passing through this layer. This is the standard school-level association; meteor heating can occur across a range of altitudes.

The correct answer is D, the exosphere. It is the outermost atmospheric layer and gradually merges into outer space. Satellites orbit at different altitudes, so not all satellites are located in the exosphere.

The correct answer is B, the troposphere. It contains most of the atmosphere’s water vapour, and its moving air helps produce clouds, winds, storms, and precipitation. These are the main reasons most ordinary weather occurs there.

The correct answer is C, the stratosphere. Most atmospheric ozone is concentrated in a region of the stratosphere called the ozone layer. This ozone absorbs much of the Sun’s harmful ultraviolet radiation before it reaches Earth’s surface.

The correct answer is A, the mesosphere. The main atmospheric layers, in order upward from Earth’s surface, are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The mesosphere therefore lies immediately above the stratosphere.

The correct answer is C, the exosphere. In the usual sequence of the main atmospheric layers—troposphere, stratosphere, mesosphere, thermosphere, and exosphere—the exosphere is outermost. It is extremely thin and gradually transitions into outer space.

The correct answer is B, the exosphere. It is the outermost atmospheric layer, where gas particles are extremely sparse. Its transition into outer space is gradual rather than marked by a sharp boundary.

The correct answer is D, the stratosphere. Most atmospheric ozone is concentrated in the stratospheric ozone layer. Ozone absorbs much of the Sun’s harmful ultraviolet radiation, reducing the amount that reaches Earth’s surface and helping protect living organisms.