Earth's Atmosphere

The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds Earth. High above the planet, the atmosphere becomes thinner until it gradually reaches space. It is divided into five layers. Most of the weather and clouds are found in the first layer.

The atmosphere is an important part of what makes Earth livable. It blocks some of the Sun's dangerous rays from reaching Earth. It traps heat, making Earth a comfortable temperature. And the oxygen within our atmosphere is essential for life.

Over the past century, greenhouse gases and other air pollutants released into the atmosphere have been causing big changes like global warming, ozone holes, and acid rain.

<a
  href="/earth/Atmosphere/clouds/stratocumulus.html&edu=high&dev=">Stratocumulus
  clouds</a> belong to the <a
  href="/earth/Atmosphere/clouds/low_cloud.html&edu=high&dev=">Low
  Cloud</a> (surface-2000m) group. These clouds are low, lumpy, and gray.  Only light <a
  href="/earth/Atmosphere/precipitation.html&edu=high&dev=">precipitation</a>,
  generally in the form of <a
  href="/earth/Atmosphere/precipitation/drizzle.html&edu=high&dev=">drizzle</a>,
  occurs with stratocumulus clouds. To distinguish between a stratocumulus and
  an <a
  href="/earth/Atmosphere/clouds/altocumulus.html&edu=high&dev=">altocumulus</a>
  cloud, point your hand toward the cloud. If the cloud is about the size of
  your fist, then it is stratocumulus.<p><small><em>            Courtesy of Carlye Calvin/UCAR</em></small></p>Anti-crepuscular rays are beams of sunlight that appear to converge on a point opposite the sun. They are similar to crepuscular rays, but are seen opposite the sun in the sky. Anti-crepuscular rays are most frequently visible near sunrise or sunset. This photo of anti-crepuscular rays was taken at sunset in Boulder, Colorado. Crepuscular rays are usually much brighter than anti-crepuscular rays.<p><small><em> Image Courtesy of Carlye Calvin</em></small></p>Greenland's <a href="http://www.windows2universe.org/earth/polar/cryosphere_glacier1.html">ice sheet</a> saw a record <a href="http://www.windows2universe.org/headline_universe/olpa/greenland_10dec07.html">melt</a> in July 2012.  Scientists studying this event have found that this melting event was triggered by an influx of unusually warm air and amplified by the presence of a blanket of thin low-level <a href="http://www.windows2universe.org/earth/Atmosphere/cloud.html">clouds</a> which pushed temperatures up above freezing.  For more information see the <a href="http://www.news.wisc.edu/21638">press release</a> from the University of Wisconsin Madison.<p><small><em>Image courtesy of University of Wisconsin-Madison</em></small></p>On May 20, 2013, a massive EF5 <a href="http://www.windows2universe.org/earth/Atmosphere/tornado.html">tornado</a> hit Moore, Oklahoma, devastating communities and lives.  The tornado, on the ground for 40 minutes, took a path through a subdivision of homes, destroying block after block of homes, and hitting two elementary schools just as school was ending as well as a hospital. Hundreds of people were injured, and 24 were killed.<p><small><em>Image courtesy of Ks0stm, Creative Commons Attribution-Share Alike 3.0 Unported license</em></small></p>How did life evolve on <a href="/earth/earth.html&edu=high&dev=">Earth</a> during the <a href="/earth/past/Archean.html&edu=high&dev=">Archean</a>, when the <a href="/sun/sun.html&edu=high&dev=">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=high&dev=">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=high&dev=">greenhouse</a> gas concentration was the same as today.  <a href="http://www.manchester.ac.uk/aboutus/news/display/?id=10798">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html&edu=high&dev=">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=high&dev=">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=high&dev=">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=high&dev=">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=high&dev=">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p><a
  href="/earth/Atmosphere/clouds/lenticular.html&edu=high&dev=">Lenticular
  clouds</a> form on the downwind side of mountains. <a
  href="/earth/Atmosphere/wind.html&edu=high&dev=">Wind</a>
  blows most types of clouds across the sky, but lenticular clouds seem to stay
  in one place. Air moves up and over a mountain, and at the point where the
  air goes past the mountaintop the lenticular cloud forms, and then the air <a
  href="/earth/Water/evaporation.html&edu=high&dev=">evaporates</a>
  on the side farther away from the mountains. This close up of lenticular
  clouds was taken at sunset on November 20, 2006 in Boulder, Colorado.<p><small><em>       Courtesy of Roberta Johnson</em></small></p>

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