Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=elem">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=elem">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="http://www.whoi.edu">Woods Hole Oceanographic Institute</a>)</em></small></p>Scientists at the University of Michigan have found that <a href="/earth/polar/cryosphere_permafrost1.html&edu=elem">permafrost</a> in the <a href="/earth/polar/polar_north.html&edu=elem">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">climate-warming</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=elem">carbon dioxide</a>, to the <a href="/earth/Atmosphere/overview.html&edu=elem">atmosphere</a> much faster than previously thought.<p><small><em>George Kling, The University of Michigan</em></small></p>An artist's rendering of the moment of impact of a massive <a
  href="/our_solar_system/meteors/meteors.html&edu=elem">meteorite</a>
  at the end of the Cretaceous (at the end of the <a
  href="/earth/geology/hist_mesozoic.html&edu=elem">Mesozoic
  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&edu=elem">mass extinction
  of dinosaurs</a> and many other life forms. Recent research suggests that
 perhaps <a
  href="/headline_universe/olpa/chicxulub.html&edu=elem">massive
  volcanic eruptions</a> may be been responsible for the extinction.<p><small><em>Courtesy of Don Davis, NASA</em></small></p>There are over 900 <a href="/the_universe/uts/megalith.html&edu=elem">rings of stone</a> located in the British Isles. The most famous of these stone rings is of course, <a href="/the_universe/uts/stonehenge.html&edu=elem">Stonehenge</a>.    The stones of Stonehenge were put in place between 3,000 B.C and 2,000 B.C. by neolithic people.Some speculate that the site was built as a temple of worship of the ancient Earth deities. Some say it was used as an <a href="/the_universe/uts/stonehenge_astro.html&edu=elem">astronomical observatory</a> of sorts. Still others say it was a burial ground.<p><small><em>  Image courtesy of Corel Photography.</em></small></p><p>The United Nations <a href="http://reliefweb.int/sites/reliefweb.int/files/resources/PAND_report.pdf" target="_blank">estimated</a> that between 1994-2015, there were 6,873 natural disasters worldwide, which affected 218 million people and claimed 1.35 million lives. </p>
<p>Check out the materials about natural disasters in <a href="/earth/natural_hazards/when_nature_strikes.html&edu=elem">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>Sinkholes are <a href="/teacher_resources/main/frameworks/esl_bi8.html&edu=elem">natural hazards</a> in many places around the world. They are formed when water dissolves underlying <a href="/earth/Water/carbonates.html&edu=elem">limestone</a>, leading to collapse of the surface.  Hydrologic conditions such as a lack of rainfall, lowered water levels, or excessive rainfall can all contribute to sinkhole development. On 2/28/2013, a sinkhole suddenly developed under the house outside of Tampa, Florida, leading to the tragic death of its occupant, Jeff Bush.<p><small><em>Image courtesy of Southwest Florida Water Management District</em></small></p>

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