Earth

Earth, our home planet, is a beautiful blue and white ball when seen from space. The third planet from the Sun, it is the largest of the inner planets. Earth is the only planet known to support life and to have liquid water at the surface. Earth has a substantial atmosphere and magnetic field, both of which are critical for sustaining life on Earth. Earth is the innermost planet in the solar system with a natural satellite – our Moon. Explore our beautiful home planet – unique in our solar system - through the links in this section.

This iconic image of Earth rising above the surface of the <a
  href="/earth/moons_and_rings.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Moon</a>,
  was taken on December 24, 1968 by astronauts on the <a
  href="/space_missions/apollo8.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Apollo 8
  mission</a>. Apollo 8 was the first <a
  href="/space_missions/manned.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">manned
  mission</a> to the Moon, and entered into lunar orbit on Christmas Eve. That
  evening, the astronauts held a live broadcast from lunar orbit, in which they showed pictures of the Earth and moon as seen from their
  spacecraft.<p><small><em> Image courtesy of   NASA</em></small></p>Scientists at the University of Michigan have found that <a href="/earth/polar/cryosphere_permafrost1.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">permafrost</a> in the <a href="/earth/polar/polar_north.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Arctic</a> is extremely sensitive to sunlight.  Exposure to sunlight releases carbon gases trapped in the permafrost, including <a href="/earth/climate/earth_greenhouse.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">climate-warming</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">carbon dioxide</a>, to the <a href="/earth/Atmosphere/overview.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">atmosphere</a> much faster than previously thought.<p><small><em>George Kling, The University of Michigan</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>As permafrost thaws, the land, atmosphere, water resources, ecosystems, and human communities are affected. Coastal areas and hillsides are vulnerable to erosion by thawing of permafrost.  Thawing permafrost also causes a positive feedback to global warming, as carbon trapped within the once-frozen soils is released as <a href="/physical_science/chemistry/methane.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">methane</a>, a powerful <a href="/earth/climate/cli_greengas.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">greenhouse gas</a>.
Watch the NBC Learn video - <a href="/earth/changing_planet/permafrost_methane_intro.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Thawing Permafrost and Methane</a> to find out more.<p><small><em>Image courtesy of the    USGS</em></small></p>A sinuous glowing band of <a
  href="/earth/Magnetosphere/aurora.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">aurora</a> (the Aurora Australis
  or Southern Lights) loops around the <a
  href="/earth/polar/polar_south.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">southern polar</a>
region in the
  distance as viewed by astronauts onboard the space shuttle on <a
  href="http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-39.html">STS-039</a>. 
  <a
  href="/earth/Magnetosphere/aurora/aurora_colors.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Aurora are produced</a>
  when <a
  href="/physical_science/physics/atom_particle/particle_radiation.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">energetic particles</a>
 entering the Earth's
  atmosphere from space interact with <a
  href="/physical_science/physics/atom_particle/atom.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">atoms</a> and <a
  href="/earth/geology/molecule.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">molecules</a> in the atmosphere and
  release energy, emitted as light.<p><small><em>Courtesy of NASA, Astronaut Overmeyer and Dr. Hallinan</em></small></p>How did life evolve on <a href="/earth/earth.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Earth</a> during the <a href="/earth/past/Archean.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Archean</a>, when the <a href="/sun/sun.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">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=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=elem&dev=1/earth/Atmosphere/moons/rocks_intro.html">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p>

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