How did life evolve on <a href="/earth/earth.html&edu=elem&dev=">Earth</a> during the <a href="/earth/past/Archean.html&edu=elem&dev=">Archean</a>, when the <a href="/sun/sun.html&edu=elem&dev=">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=elem&dev=">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=elem&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=elem&dev=">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=elem&dev=">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=elem&dev=">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=elem&dev=">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=elem&dev=">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p>As temperatures rise and soil moisture decreases, plants are stressed, which can lead to <a href="/earth/climate/crops_withering.html&edu=elem&dev=">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html&edu=elem&dev=">Droughts</a> accompanied by increased temperatures can lead to famine, social and political disruptions. Scientists are  helping with early identification of drought that might trigger food shortages. Watch the NBC Learn video - <a href="/earth/changing_planet/withering_crops_intro.html&edu=elem&dev=">Changing Planet: Withering Crops</a> to find out more.<p><small><em>Image taken by Tomas Castelazo, Creative Commons <a href=&quot;http://creativecommons.org/licenses/by/3.0/deed.en&quot;>Attribution 3.0 Unported</a> license.</em></small></p>New observations by the MESSENGER spacecraft provide  support for the hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed (shown in red) polar craters. Areas where polar deposits of ice imaged by Earth-based radar are shown in yellow.<p><small><em>Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory</em></small></p>Lunar eclipses are special events that only occur when certain conditions are met. First of all, the Moon must be in <a href="/the_universe/uts/moon3.html&edu=elem&dev=">full phase</a>. Secondly, the <a href="/sun/sun.html&edu=elem&dev=">Sun</a>, <a href="/earth/earth.html&edu=elem&dev=">Earth</a> and <a href="/earth/moons_and_rings.html&edu=elem&dev=">Moon</a> must be in a perfectly straight line. If both of these are met, then the Earth's shadow can block the Sun's light from hitting the Moon.  The reddish glow of the Moon is caused by light from the Earth's limb scattering toward the Moon, which is reflected back to us from the Moon's surface.<p><small><em>Image credit - Doug Murray, Palm Beach Gardens, Florida</em></small></p>A near-Earth <a href="/our_solar_system/asteroids.html&edu=elem&dev=">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=elem&dev=">Moon</a> and even geosynchronous <a href="/space_missions/satellites.html&edu=elem&dev=">satellites</a>, it didn't strike Earth!  Find out more from <a href="http://www.nasa.gov/mission_pages/asteroids/news/asteroid20130201315144.html">NASA</a>! Fragments of a meteorite hit Chelyabinsk, Russia on 2/15/2013 <a href="http://www.reuters.com/article/2013/02/15/us-russia-meteorite-idUSBRE91E05Z20130215">injuring over 500</a>. Learn about <a href="http://www.windows2universe.org/our_solar_system/meteors/meteors.html">meteors and meteorites</a>.<p><small><em>NASA/JPL-CalTech</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>

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