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<h3>Learning Objective</h3>
<ul>
<li>Recall the <a data-lesson="composition" data-subject="chemistry" data-tutorial="quantitative-aspects-chemical-change" href="https://app.ulearngo.com/chemistry/quantitative-aspects-chemical-change/composition">composition</a> and relative amounts of the various <a data-lesson="introducing-gases" data-subject="chemistry" data-tutorial="gases" href="https://app.ulearngo.com/chemistry/gases/introducing-gases">gases</a> that make up the Earth’s atmosphere and how the atmosphere helps the planet survive</li>
</ul>
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<div>
<h3>Key Points</h3>
<ul>
<li>Atmospheric stratification describes the structure of the atmosphere, dividing it into distinct layers, each with specific characteristics such as <a data-lesson="conversion-temperature-units" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/conversion-temperature-units">temperature</a> or composition.</li>
<li>Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% <a data-lesson="carbon" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/carbon">carbon</a> dioxide, and small amounts of other gases.</li>
<li>The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and warming the <a data-lesson="surface-area-and-reaction-rates" data-subject="chemistry" data-tutorial="energy-and-chemical-reactions" href="https://app.ulearngo.com/chemistry/energy-and-chemical-reactions/surface-area-and-reaction-rates">surface</a> through <a data-lesson="calorimetry" data-subject="chemistry" data-tutorial="thermochemistry" href="https://app.ulearngo.com/chemistry/thermochemistry/calorimetry">heat</a> retention (the greenhouse effect).</li>
<li>The atmosphere is further classified into multiple layers by temperature, which include the thermosphere, the mesosphere, the stratosphere, and the troposphere.</li>
<li>In general, air <a data-lesson="gas-pressure" data-subject="chemistry" data-tutorial="gases" href="https://app.ulearngo.com/chemistry/gases/gas-pressure">pressure</a> and density decrease with altitude in the atmosphere.</li>
</ul>
</div>
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<h3>Terms</h3>
<ul>
<li><strong>ozone layer:</strong> a region of the stratosphere that absorbs most solar ultraviolet radiation; in the past century, the release of CFCs has caused a hole to appear in this layer</li>
<li><strong>atmosphere: </strong>a layer of gases that may surround a material body of sufficient mass, such as the Earth, and that is held in place by the body’s gravity</li>
<li><strong>greenhouse gas:</strong> a <a data-lesson="radioactive-decay-series" data-subject="chemistry" data-tutorial="nuclear-chemistry" href="https://app.ulearngo.com/chemistry/nuclear-chemistry/radioactive-decay-series">series</a> of <a data-lesson="compounds-2" data-subject="chemistry" data-tutorial="quantitative-aspects-chemical-change" href="https://app.ulearngo.com/chemistry/quantitative-aspects-chemical-change/compounds-2">compounds</a> that are particularly adept at trapping heat; as a result, the Earth is beginning to warm</li>
</ul>
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<p>The Earth’s atmosphere is composed of a layer of gases that encase the planet and that are constrained by gravitational forces.</p>
<div class="wp-caption alignnone" style="width: 680px"><img alt="" height="452" src="https://data.ulearngo.com/assets/b323f0e7-e983-438f-9867-b7d8a03efa7e" width="680"/><p class="wp-caption-text"><b>The Earth’s atmosphere</b>: A view of the Earth from space, looking from orbit beyond the exosphere, down through the layers of the thermosphere, mesosphere, and stratosphere, at a thick cloud layer topping the troposphere.</p></div>
<p>In the 1800s, scientists, including John Dalton, realized that the atmosphere was composed of a variety of gases. By volume, air is made up of approximately 78% nitrogen, 21% oxygen, and 1% argon, with small amounts of additional gases including <a data-lesson="unique-properties-of-water" data-subject="chemistry" data-tutorial="states-of-matter" href="https://app.ulearngo.com/chemistry/states-of-matter/unique-properties-of-water">water</a> <a data-lesson="vaporization-and-condensation" data-subject="chemistry" data-tutorial="liquids-and-solids" href="https://app.ulearngo.com/chemistry/liquids-and-solids/vaporization-and-condensation">vapor</a> and carbon dioxide. While the three major components have remained relatively constant over <a data-lesson="chemical-reaction-rates" data-subject="chemistry" data-tutorial="chemical-kinetics" href="https://app.ulearngo.com/chemistry/chemical-kinetics/chemical-reaction-rates">time</a> and space, the minor components, which also include methane, <a data-lesson="sulfur" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/sulfur">sulfur</a> dioxide, ozone, and <a data-lesson="occurrence-preparation-and-properties-of-nitrogen" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-properties-of-nitrogen">nitrogen</a> oxides, have varied more widely. These minor components are the major contributors to phenomena like weather, the greenhouse effect, and global warming.</p>
<p>In recent years, additional carbon dioxide has helped trap additional heat being radiating off the planet. Carbon dioxide, water vapor, and other <a data-lesson="the-greenhouse-effect" data-subject="chemistry" data-tutorial="chemistry-real-world" href="https://app.ulearngo.com/chemistry/chemistry-real-world/the-greenhouse-effect">greenhouse gases</a> are adept at stopping heat from leaving the atmosphere, causing the Earth to heat up. Some greenhouse gases are beneficial—without them, Earth would be as cold as the moon—but the recent increase in carbon dioxide has upset the precise balance between too cold, too hot, and just right.</p>
<p>The atmosphere is further classified into multiple layers by temperature, which include the thermosphere, the mesosphere, the stratosphere, and the troposphere. Both air pressure and density increase upon approaching the Earth’s surface. The layer closest to the Earth, the troposphere, contains most of the water vapor and is where <a data-lesson="meteorology-climatology-and-atmospheric-science" data-subject="chemistry" data-tutorial="gases" href="https://app.ulearngo.com/chemistry/gases/meteorology-climatology-and-atmospheric-science">weather</a> occurs. The next layer, the stratosphere, contains an <a data-lesson="polar-ozone-holes" data-subject="chemistry" data-tutorial="chemistry-real-world" href="https://app.ulearngo.com/chemistry/chemistry-real-world/polar-ozone-holes">ozone layer</a> that results from the reaction of ionizing solar radiation with <a data-lesson="occurrence-preparation-and-compounds-of-oxygen" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-compounds-of-oxygen">oxygen</a> gas; this ozone layer is responsible for the absorption of UV light.</p>
<p>In the recent past, we have damaged our ozone layer by putting chlorofluorocarbons (CFCs) into the atmosphere. The CFCs have damaged ozone, resulting in a hole in the ozone layer. In recent years, CFCs have been banned and the ozone layer hole is shrinking. Farther from the surface, the mesosphere, the thermosphere, and then the exosphere make up the top layers of our atmosphere. Planes typically fly in the stratosphere.</p>
<p>The atmosphere performs a various beneficial functions for the inhabitants of Earth including: absorbing UV radiation, heating the Earth’s surface, and buffering temperature fluctuations.</p>

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Earth's Atmosphere

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Earth's Atmosphere

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