Earth's Interior and Surface

Earth, the largest and densest rocky planet, was formed about 4.5 billion years ago. The Earth's interior is divided into four layers, which is typical of rocky planets. Each layer has different characteristics and is made of different elements and minerals.

There are many different types of features on Earth’s surface due to the complexity of our planet. The surface is unique from the other planets because it is the only one which has liquid water in such large quantities. Water forms some features of Earth's surface such as rivers, oceans, beaches and lakes. Other surface features, such as mountains, earthquakes and volcanoes, are formed when large pieces of the Earth’s outer layer move slowly by plate tectonics.

Bison roaming on mixed grass prairie - a type of <a
  href="/php/tour_test_sqli.php?page=/earth/grassland_eco.html&edu=high">grassland</a>
  - at Wind Cave National Park (U.S.).  Over one quarter of the Earth's surface
  is covered by grasslands. Grasslands are found on every continent except <a
  href="/php/tour_test_sqli.php?page=/earth/polar/polar_south.html&edu=high">Antarctica</a>,
  and they make up most of Africa and Asia. Grasslands develop where there
  isn't enough rain for <a
  href="/php/tour_test_sqli.php?page=/earth/forest_eco.html&edu=high">forests</a>
  but there is too much rain for <a
  href="/php/tour_test_sqli.php?page=/earth/desert_eco.html&edu=high">deserts</a>.
  Grasslands are filled with - you guessed it - grass.<p><small><em>        National Park Service</em></small></p>Gold or Fool’s Gold? There are two easy ways to tell Fool’s Gold, the
  <a
  href="/php/tour_test_sqli.php?page=/earth/geology/min_intro.html&edu=high">mineral</a>
  <a
  href="/php/tour_test_sqli.php?page=/earth/geology/min_pyrite.html&edu=high">pyrite</a>,
  from real gold. First, pyrite leaves a black streak on a white tile whereas
  gold leaves, well, a gold streak. Also, pyrite is much harder than gold.
  Pyrite is made up of the <a
  href="/php/tour_test_sqli.php?page=/earth/geology/periodic_table.html&edu=high">elements</a>
  iron (Fe) and sulfur (S).  Both of these two elements are among the <a
  href="/php/tour_test_sqli.php?page=/earth/geology/crust_elements.html&edu=high">eight
  most abundant</a> in the <a
  href="/php/tour_test_sqli.php?page=/earth/interior/earths_crust.html&edu=high">Earth’s
  crust</a>.<p><small><em> Courtesy of Corel</em></small></p>This is the Barringer Meteor Crater in Arizona. The diameter is 1.2
  kilomters, and it is 49,000 years old. Compared with other planets, <a
  href="/php/tour_test_sqli.php?page=/earth/Interior_Structure/crater.html&edu=high">impact
  craters</a> are rare <a
  href="/php/tour_test_sqli.php?page=/earth/Interior_Structure/surface_features.html&edu=high">surface
  features</a> on Earth. There are two main reasons for the low number of
  craters. One is that our <a
  href="/php/tour_test_sqli.php?page=/earth/Atmosphere/overview.html&edu=high">atmosphere</a>
  burns up most <a
  href="/php/tour_test_sqli.php?page=/our_solar_system/meteors/meteors.html&edu=high">meteoroids</a>
  before they reach the surface. The other reason is that Earth's surface is <a
  href="/php/tour_test_sqli.php?page=/earth/interior/plate_tectonics.html&edu=high">continually
  active</a> and erases the marks of craters over time.<p><small><em>D. Roddy and LPI</em></small></p>Hydrothermal vents in the deep ocean are located at tectonic <a
  href="/php/tour_test_sqli.php?page=/earth/interior/seafloor_spreading.html&edu=high">spreading
  ridges</a>. While most of the water in the deep ocean is close to freezing,
  the water at hydrothermal vents is very hot and laden with chemicals.  In
  this <a
  href="/php/tour_test_sqli.php?page=/earth/extreme_environments.html&edu=high">extreme
  environment</a>, certain species of <a
  href="/php/tour_test_sqli.php?page=/earth/Life/archaea.html&edu=high">Archaea</a>
  and <a
  href="/php/tour_test_sqli.php?page=/earth/Life/classification_eubacteria.html&edu=high">Eubacteria</a>
  thrive, enabling a unique <a
  href="/php/tour_test_sqli.php?page=/earth/Water/life_deep.html&edu=high">food
  chain</a> including fish, shrimp, giant tubeworms, mussels, crabs, and clams.<p><small><em> Courtesy of NASA</em></small></p>An <a href="http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc000905e.php">8.6 magnitude earthquake</a> struck on 11 April 2012 off of Banda Aceh, Sumatra, Indonesia, followed by a strong aftershock.  Earthquake motion was primarily horizontal.  A tsunami warning was issued for the Indian Ocean, but was cancelled at 12:36 UTC.  A tsunami was observed at 1 meter or less. Find out more about <a href="/php/tour_test_sqli.php?page=/earth/geology/quake_1.html&edu=high">earthquake</a> and <a href="/php/tour_test_sqli.php?page=/earth/tsunami1.html&edu=high">tsunami</a> processes. Check out the resources <a href="/php/tour_test_sqli.php?page=/teacher_resources/2011_AGU-NESTA_GIFT_Workshop.html&edu=high">here</a>.<p><small><em>NOAA</em></small></p>Sinkholes are <a href="/php/tour_test_sqli.php?page=/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="/php/tour_test_sqli.php?page=/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>

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