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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>How did life evolve on <a href="/earth/earth.html">Earth</a> during the <a href="/earth/past/Archean.html">Archean</a>, when the <a href="/sun/sun.html">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html">greenhouse</a> gas concentration was the same as today.  <a href="">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</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">methane</a>, a powerful <a href="/earth/climate/cli_greengas.html">greenhouse gas</a>.
Watch the NBC Learn video - <a href="/earth/changing_planet/permafrost_methane_intro.html">Thawing Permafrost and Methane</a> to find out more.<p><small><em>Image courtesy of the    USGS</em></small></p>This first global map of <a href="">ocean</a> surface saltiness, released in September 2012 by the NASA Aquarius mission team, shows the distribution of salt in the first 2 cm of the Earth's ocean. <a href="">Salinity</a> variations are one of the main drivers of <a href="">ocean circulation</a>, and are closely connected with the <a href="">cycling of freshwater</a> around the planet. High salinity is seen in the Mediterranean, Atlantic, and the Arabian Sea.<p><small><em>Image courtesy of NASA/GSFC/JPL-Caltech</em></small></p>As temperatures rise and soil moisture decreases, plants are stressed, which can lead to <a href="/earth/climate/crops_withering.html">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html">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">Changing Planet: Withering Crops</a> to find out more.<p><small><em>Image taken by Tomas Castelazo, Creative Commons <a href=&quot;;>Attribution 3.0 Unported</a> license.</em></small></p>According to <a href="">NASA scientists</a>, the Voyager 1 spacecraft entered interstellar space in August 2012, becoming the first spacecraft to leave the <a href="/our_solar_system/solar_system.html">solar system</a>. The space probe is about 19 billion km from the <a href="/sun/sun.html">Sun</a>.  <a href="/space_missions/voyager.html">Voyager 1 and 2</a> were launched in 1977 on a <a href="/space_missions/voyager.html">mission</a> that flew them both by <a href="/jupiter/jupiter.html">Jupiter</a> and <a href="/saturn/saturn.html">Saturn</a>, with Voyager 2 continuing to <a href="/uranus/uranus.html">Uranus</a> and <a href="/neptune/neptune.html">Neptune</a>. Voyager 2 is the longest continuously operated spacecraft. It is about 15 billion km away from the <a href="/sun/sun.html">Sun</a>.<p><small><em>Image courtesy of NASA</em></small></p>

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