Layers of the atmosphere

Answer: A. Stratospheric ozone absorbs some of the Sun’s ultraviolet radiation, and the absorbed energy warms the air. As a result, temperature generally increases with height through much of the stratosphere, unlike in the troposphere, where it generally decreases with height.

The correct answer is A. Ozone in the stratosphere absorbs much of the Sun’s harmful ultraviolet radiation. If the ozone layer thins, more ultraviolet radiation can reach Earth’s surface, increasing risks such as skin and eye damage. Ozone depletion does not convert nitrogen into food or remove all atmospheric water vapour.

A is correct. Stratospheric ozone absorbs much of the Sun’s harmful ultraviolet radiation, especially UV-B. If the ozone layer thins, more UV-B can reach Earth’s surface and may damage sensitive plants or disrupt parts of ecosystems. These effects can influence agriculture, though their extent depends on the crop and local conditions.

Correct answer: C. Stratospheric ozone absorbs harmful ultraviolet radiation and helps protect living things. Near the ground, ozone can form through sunlight-driven reactions involving pollutants such as nitrogen oxides and volatile organic compounds. At high concentrations, it can harm health and plants, so lower-atmosphere ozone is considered a pollutant. Its role therefore depends on altitude.

D is correct. The exosphere is the outermost atmospheric layer and is commonly associated with artificial satellites in simplified school descriptions. Satellite orbits occur at different altitudes, however, so not all satellites orbit within the exosphere. The other options name lower atmospheric layers.

Correct answer: B. In the stratosphere, temperature generally increases with height because ozone absorbs ultraviolet radiation. This temperature pattern makes the air stable and suppresses strong vertical convection and mixing. As a result, the stratosphere is relatively calm; most clouds and storms develop in the troposphere.

B is correct. The stratosphere is relatively stable, so strong vertical convection and mixing are limited. Aircraft can therefore often experience smoother conditions there, although turbulence is still possible.

Correct answer: C. Temperature generally decreases as altitude increases through the mesosphere. Therefore, temperatures become extremely low near its upper boundary, the mesopause, which is one of the coldest regions of Earth’s atmosphere. The ozone layer is concentrated mainly in the stratosphere, while ordinary rain-producing weather occurs mainly in the troposphere.

The correct answer is B. The exosphere is the extremely thin outermost region of Earth’s atmosphere. Hydrogen and helium have very low molecular masses and can diffuse through the upper atmosphere more readily than heavier gases, so they are relatively prominent there. They are not heavy gases, and they do not form rainfall or ozone.

The correct answer is D. In the thermosphere, temperature generally increases with altitude because its sparse gases absorb high-energy solar radiation. The other trends are different: temperature generally decreases with height in the troposphere and mesosphere, but increases in the stratosphere due largely to ozone absorption of ultraviolet radiation.

The correct answer is C, the mesosphere. Temperature generally decreases with height in this layer, and many meteoroids heat up and burn as they enter the atmosphere in or around it. In the stratosphere, by contrast, temperature generally increases with height because ozone absorbs ultraviolet radiation.

Correct answer: D. Earth’s gravity pulls atmospheric gases toward the surface, so most air is concentrated in the lower atmosphere. As altitude increases, there are generally fewer gas molecules in a given volume, and density decreases. Temperature can affect density locally, but gravity explains this broad pattern.

Answer: C, stratopause and stratosphere. The stratopause is the upper boundary of the stratosphere, above which the mesosphere begins. The tropopause bounds the troposphere, and the mesopause is at the top of the mesosphere. “River sphere” is not an atmospheric layer.

Answer: A, the thermosphere. Auroras form when energetic particles from the Sun interact with gases high in the atmosphere, causing them to emit light. The auroral region is associated with the ionosphere and spans a range of altitudes, but it is commonly linked to the thermosphere in school-level descriptions.

The correct answer is A. The troposphere is the lowest layer and is heated mainly from the Earth’s surface. Warm air rises, cool air sinks, and this produces convection, clouds, winds and most ordinary weather. Above it, the stratosphere is comparatively stable. Ozone absorbs ultraviolet radiation and causes a general increase of temperature with height in the stratosphere, which reduces strong vertical mixing and ordinary weather turbulence. Option B is wrong because water vapour is not suddenly very high in the stratosphere; most atmospheric moisture is concentrated in the troposphere. Option C is wrong because many meteors burn mainly in the mesosphere, not because of the transition from the troposphere to the stratosphere. Option D is wrong because the atmosphere continues above the stratosphere through the mesosphere, thermosphere and exosphere. The memory cue is: “Troposphere—weather; stratosphere—stability.”

The correct answer is B, the mesosphere. Temperature decreases with altitude in the mesosphere, reaching a minimum near its upper boundary, the mesopause. Above it, temperature rises in the thermosphere as that layer absorbs energetic solar radiation.

The correct answer is B. The ionosphere is identified by ionized particles rather than by a single sharp altitude boundary. Solar radiation ionizes gases across a range of heights, and the ionosphere overlaps parts of other atmospheric regions, especially the mesosphere and thermosphere. It is not below the troposphere, ocean-only, or made of soil.

The correct answer is A. Temperature reflects the particles’ average kinetic energy, while density describes how many particles are in a given volume. Thermosphere particles can have high kinetic energy, but they are very far apart. With so few particles and collisions, heat is not transferred as it is in dense air near Earth’s surface. High temperature therefore does not mean the air would feel like ordinary hot air.

The governing concept is the contrasting temperature gradient in the lower atmospheric layers. In the troposphere, temperature generally decreases with height because the surface is the main source of heating. In the stratosphere, ozone absorbs ultraviolet radiation, so temperature generally increases upward. The two layers therefore do not have identical temperatures or rainfall, and option A correctly states both trends.

The correct answer is B. The main concentration of atmospheric ozone is in the stratosphere, not the mesosphere. The troposphere is where most weather occurs, and ionization is a feature of the upper atmosphere associated with the thermosphere and ionosphere. Thus, B is the mismatched pair.

A is correct. Auroras form when energetic charged particles from the Sun enter the upper atmosphere and interact with atmospheric gases. Earth’s magnetic field guides many of these particles toward the polar regions. The resulting glow shows that the upper atmosphere is affected by solar particles and magnetic effects. The main ozone-rich region is in the stratosphere, while rivers and ordinary rainfall are surface or lower-atmosphere phenomena.

The correct answer is A. Ozone absorbs ultraviolet radiation from the Sun and warms the stratosphere. This absorption contributes to the temperature increase with height in much of the stratosphere. Without ozone, that warming—and therefore this upward temperature trend—would be reduced.

The correct answer is A, the ionosphere. Energetic solar radiation ionizes some particles in the upper atmosphere, creating charged particles that can affect the propagation of radio waves. This connection to ionization and radio communication identifies the ionosphere.

The correct answer is A. The exosphere is the outermost, extremely rarefied region of Earth’s atmosphere. Its particles are far apart, and light gases such as hydrogen and helium can be present at great heights. Heavy rain, abundant water vapour and most active weather are associated mainly with the denser troposphere, not the exosphere.

The correct answer is A. The tropopause is the transition boundary between the troposphere and the stratosphere. Most clouds and weather occur in the troposphere below it. The main ozone-rich region is within the stratosphere, while many meteors become visible as they burn in the mesosphere.