Atmosphere

{
  "id": "MLC-T-ENV-002315",
  "term": "Atmosphere",
  "field": "Environment",
  "definition": "1. The air or gases that surround a planetary body such as the Earth.\n\n2. A mixture of nitrogen, oxygen, carbon dioxide, and other gases that surrounds the Earth. The atmosphere is critical to supporting life on Earth.\n\n3. The gaseous envelope surrounding the Earth. The dry atmosphere consists almost entirely of nitrogen (78.1% volume mixing ratio) and oxygen (20.9% volume mixing ratio), together with a number of trace gases, such as argon (0.93% volume mixing ratio), helium, radiatively active greenhouse gases such as carbon dioxide (0.035% volume mixing ratio), and ozone. In addition the atmosphere contains water vapor, whose amount is highly variable but typically 1% volume mixing ratio. The atmosphere also contains clouds and aerosols.\n\n4. The mixture of gases surrounding the Earth. The Earth's atmosphere consists of about 79.1 percent nitrogen (by volume), 20.9 percent oxygen, 0.036 percent carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally determined by its thermal properties (temperature). The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 kilometers (about 5 miles) in the polar regions and up to 17 kilometers (nearly 11 miles) above the equator. The stratosphere, which reaches to an altitude of about 50 kilometers (31miles) lies atop the troposphere. The mesosphere, which extends from 80 to 90 kilometers atop the stratosphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers.\n\n5. A standard unit of pressure exerted by a 29.92-inch column of mercury at sea level and equal to 1000 grams per square centimeter.",
  "subject": "Climate change",
  "references": [
    "Acid Rain Glossary",
    "Student's Guide to Global Climate Change",
    "Glossary of Climate Change Terms",
    "Greenhouse Gas Emissions",
    "I-BEAM Glossary of Terms"
  ],
  "url": "https://mlchart.com/terminology/environment/atmosphere/"
}