How did life evolve on <a href="/earth/earth.html&dev=">Earth</a> during the <a href="/earth/past/Archean.html&dev=">Archean</a>, when the <a href="/sun/sun.html&dev=">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&dev=">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&dev=">greenhouse</a> gas concentration was the same as today.  <a href="">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html&dev=">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&dev=">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&dev=">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&dev=">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&dev=">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</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&dev=">solar system</a>. The space probe is about 19 billion km from the <a href="/sun/sun.html&dev=">Sun</a>.  <a href="/space_missions/voyager.html&dev=">Voyager 1 and 2</a> were launched in 1977 on a <a href="/space_missions/voyager.html&dev=">mission</a> that flew them both by <a href="/jupiter/jupiter.html&dev=">Jupiter</a> and <a href="/saturn/saturn.html&dev=">Saturn</a>, with Voyager 2 continuing to <a href="/uranus/uranus.html&dev=">Uranus</a> and <a href="/neptune/neptune.html&dev=">Neptune</a>. Voyager 2 is the longest continuously operated spacecraft. It is about 15 billion km away from the <a href="/sun/sun.html&dev=">Sun</a>.<p><small><em>Image courtesy of NASA</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&dev=">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>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&dev=">methane</a>, a powerful <a href="/earth/climate/cli_greengas.html&dev=">greenhouse gas</a>.
Watch the NBC Learn video - <a href="/earth/changing_planet/permafrost_methane_intro.html&dev=">Thawing Permafrost and Methane</a> to find out more.<p><small><em>Image courtesy of the    USGS</em></small></p>An artist's rendering of the moment of impact of a massive <a
  at the end of the Cretaceous (at the end of the <a
  Era</a>). Many
  scientists have concluded for decades that a meteorite four to six kilometers
  in diameter impacted the Earth at this time, resulting in a <a
  href="/earth/past/KTextinction.html&dev=">mass extinction
  of dinosaurs</a> and many other life forms. Recent research suggests that
 perhaps <a
  volcanic eruptions</a> may be been responsible for the extinction.<p><small><em>Courtesy of Don Davis, NASA</em></small></p><p>You don't normally see <a href="/space_weather/space_weather.html&dev=">space weather</a> forecasted on the evening news, but it does impact life on <a href="/earth/earth.html&dev=">Earth</a> in many ways. What are the threats posed from all of these natural disasters and how can we work to mitigate those threats beforehand? </p>
<p>Check out the materials about natural disasters in <a href="/earth/natural_hazards/when_nature_strikes.html&dev=">NBC Learn Videos</a>, and their earth system science connections built up by the related secondary classroom activities.</p><p><small><em>NBC Learn</em></small></p>

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