An artist's rendering of the moment of impact of a massive <a
  href="/our_solar_system/meteors/meteors.html&edu=high">meteorite</a>
  at the end of the Cretaceous (at the end of the <a
  href="/earth/geology/hist_mesozoic.html&edu=high">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=high">mass extinction
  of dinosaurs</a> and many other life forms. Recent research suggests that
 perhaps <a
  href="/headline_universe/olpa/chicxulub.html&edu=high">massive
  volcanic eruptions</a> may be been responsible for the extinction.<p><small><em>Courtesy of Don Davis, NASA</em></small></p>Sinkholes are <a href="/teacher_resources/main/frameworks/esl_bi8.html&edu=high">natural hazards</a> in many places around the world. They are formed when water dissolves underlying <a href="/earth/Water/carbonates.html&edu=high">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>According to a Greek legend, the sea god Poseidon placed the figure of <a href="/the_universe/Constellations/circumpolar/cassiopeia.html&edu=high">Cassiopeia</a> among the stars. It is said that Cassiopeia has a ridiculous upside-down position to punish her for having been pretentious.<p><small><em>Image courtesy of 1995 Visual Language (c). All rights reserved.</em></small></p>Scientists at the University of Michigan have found that <a href="/earth/polar/cryosphere_permafrost1.html&edu=high">permafrost</a> in the <a href="/earth/polar/polar_north.html&edu=high">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=high">climate-warming</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=high">carbon dioxide</a>, to the <a href="/earth/Atmosphere/overview.html&edu=high">atmosphere</a> much faster than previously thought.<p><small><em>George Kling, The University of Michigan</em></small></p>How did life evolve on <a href="/earth/earth.html&edu=high">Earth</a> during the <a href="/earth/past/Archean.html&edu=high">Archean</a>, when the <a href="/sun/sun.html&edu=high">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=high">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=high">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=high">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=high">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=high">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=high">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=high">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p>A new study has found that <a href="/earth/Atmosphere/airpollution_intro.html&edu=high">pollution</a> from <a href="/earth/Atmosphere/particulates.html&edu=high">fine particles</a> in the air - mainly the result of burning coal or <a href="/earth/interior/eruptions.html&edu=high">volcanic eruptions</a> - can shade <a href="/earth/Life/cnidarian.html&edu=high">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="http://www.exeter.ac.uk/news/featurednews/title_278202_en.html">press release</a>.<p><small><em>Image courtesy of Toby Hudson (Wikimedia Commons)</em></small></p>

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