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Become a nitrogen atom in the nitrogen cycle in our Traveling Nitrogen Classroom Activity Kit/Game. See all our games, activity kits and classroom activities.
How did life evolve on <a href="/earth/earth.html&edu=high&dev=1">Earth</a> during the <a href="/earth/past/Archean.html&edu=high&dev=1">Archean</a>, when the <a href="/sun/sun.html&edu=high&dev=1">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=high&dev=1">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=high&dev=1">greenhouse</a> gas concentration was the same as today.  <a href="">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html&edu=high&dev=1">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=high&dev=1">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=high&dev=1">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=high&dev=1">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=high&dev=1">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p>Stars don't last forever. Occasionally, a star bigger than our Sun will end its life in a huge explosion, called a <a href="/the_universe/supernova.html&edu=high&dev=1">supernova</a>. The center of the star collapses in less than a second, blowing away the outer layers of the star.  There are many beautiful images of supernova remnants, the expanding shell of gas made up of the outer layers of the original star. This image is the Vela Supernova Remnant.<p><small><em>Image courtesy of the Anglo-Australian Observatory/Royal Observatory Edinburgh</em></small></p>This image is a montage of high resolutions photographs of the Earth taken in January 2012 by the Visible/Infrared Imager Radiometer Suite (VIIRS) instrument on the Suomi NPP satellite.  The image shows many stunning details of <a href="">our home planet</a> - <a href="">particularly at high resolution</a>. The beauty of our planet is obvious from space - our blue <a href="">waters</a>, our white <a href="">clouds</a>, and the green from <a href="">life</a> abundant at the surface.<p><small><em>Image courtesy of NASA</em></small></p>A near-Earth <a href="/our_solar_system/asteroids.html&edu=high&dev=1">asteroid</a> - named 2012 DA14 by astronomers  passed within 17,200 miles from Earth on February 15, 2013. On closest approach at about 1:25 p.m. CST on February 15, although it was within the orbit of the <a href="/earth/moons_and_rings.html&edu=high&dev=1">Moon</a> and even geosynchronous <a href="/space_missions/satellites.html&edu=high&dev=1">satellites</a>, it didn't strike Earth!  Find out more from <a href="">NASA</a>! Fragments of a meteorite hit Chelyabinsk, Russia on 2/15/2013 <a href="">injuring over 500</a>. Learn about <a href="">meteors and meteorites</a>.<p><small><em>NASA/JPL-CalTech</em></small></p>A new study has found that <a href="/earth/Atmosphere/airpollution_intro.html&edu=high&dev=1">pollution</a> from <a href="/earth/Atmosphere/particulates.html&edu=high&dev=1">fine particles</a> in the air - mainly the result of burning coal or <a href="/earth/interior/eruptions.html&edu=high&dev=1">volcanic eruptions</a> - can shade <a href="/earth/Life/cnidarian.html&edu=high&dev=1">corals</a> from sunlight and cool the surrounding water resulting in reduced growth rates.  Coral growth rates in the Caribbean were affected by volcanic aerosol emissions in the early 20th century and by aerosol emissions caused by humans in the later 20th century.  For more information, see the <a href="">press release</a>.<p><small><em>Image courtesy of Toby Hudson (Wikimedia Commons)</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>

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA