Layers of the Atmosphere — Reading Comprehension Lesson

Reading Passage

Layers of the Atmosphere

Earth is surrounded by a layer of gases called the atmosphere, held in place by gravity. The atmosphere is essential for life: it provides the oxygen we breathe, protects us from harmful solar radiation, regulates temperature, and is where all weather occurs. The atmosphere is not uniform but divided into distinct layers based on temperature patterns. From the surface upward, these layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer has distinct characteristics, and the boundaries between them are marked by changes in the direction of temperature change.

The troposphere is the lowest layer, extending from the surface to about 7 to 10 miles up (higher at the equator, lower at the poles). It contains about 75 percent of the atmosphere’s total mass and almost all of its water vapor and weather. Temperature decreases with altitude in the troposphere — roughly 3.5°F per 1,000 feet — which is why mountaintops are cold and why commercial aircraft, which fly near the top of the troposphere, need pressurized cabins. Above the troposphere lies the tropopause, a boundary where temperatures stop falling.

The stratosphere extends from about 7 to 31 miles above the surface. Unlike the troposphere, temperatures in the stratosphere increase with altitude, because the ozone layer — concentrated between about 9 and 22 miles up — absorbs ultraviolet radiation from the sun, heating the surrounding air. The ozone layer is essential for life on Earth because it shields the surface from harmful UV radiation that would damage DNA and cause skin cancer. Above the stratosphere is the mesosphere, extending to about 53 miles, where temperatures again decrease with altitude and reach the coldest point in the atmosphere — about −130°F. Most meteors burn up in the mesosphere.

Above the mesosphere lies the thermosphere, extending to about 375 miles. Despite its name, the thermosphere’s extremely high temperatures — up to 3,600°F — would not feel hot to a person because the air is so thin that there are very few molecules to transfer heat. The International Space Station orbits within the thermosphere. The aurora borealis (northern lights) and aurora australis (southern lights) occur in the thermosphere when charged particles from the sun collide with atmospheric gases. The outermost layer, the exosphere, gradually fades into outer space and is where satellites orbit. There is no sharp boundary between the exosphere and space.

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