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="/earth/grassland_eco.html&edu=high&dev=">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="/earth/polar/polar_south.html&edu=high&dev=">Antarctica</a>,
  and they make up most of Africa and Asia. Grasslands develop where there
  isn't enough rain for <a
  href="/earth/forest_eco.html&edu=high&dev=">forests</a>
  but there is too much rain for <a
  href="/earth/desert_eco.html&edu=high&dev=">deserts</a>.
  Grasslands are filled with - you guessed it - grass.<p><small><em>        National Park Service</em></small></p>Rainforest vegetation on the Caribbean island of Dominica. <a href="/earth/rainforest.html&edu=high&dev=">Tropical
  rainforests</a> are home to thousands of species of animals, plants, fungi and
  microbes. Scientists suspect that there are many species living in
  rainforests have not yet been found or described. Rainforests get their name
  because they receive a lot of rain - an average of 80 inches (203 cm) a year!<p><small><em>     NBII Digital Image Library - Randolph Femmer, photographer</em></small></p>Gold or Fool's Gold? There are two easy ways to tell Fool's Gold, the
  <a
  href="/earth/geology/min_intro.html&edu=high&dev=">mineral</a>
  <a
  href="/earth/geology/min_pyrite.html&edu=high&dev=">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="/earth/geology/periodic_table.html&edu=high&dev=">elements</a>
  iron (Fe) and sulfur (S). Both of these two elements are among the <a
  href="/earth/geology/crust_elements.html&edu=high&dev=">eight
  most abundant</a> in the <a
  href="/earth/interior/earths_crust.html&edu=high&dev=">Earth's
  crust</a>.<p><small><em> Courtesy of Corel</em></small></p>The most majestic of the volcanoes are composite volcanoes, also
  known as strato-volcanoes. Unlike the <a
  href="/earth/interior/shield_volcanos.html&edu=high&dev=">shield
  volcanoes</a> which are flat and broad, composite volcanoes are tall,
  symmetrically shaped, with steep sides, sometimes rising 10,000 feet high.
  They are built of alternating layers of <a
  href="/earth/interior/lava.html&edu=high&dev=">lava</a>
  flows, volcanic <a
  href="/earth/interior/ash.html&edu=high&dev=">ash</a>,
  cinders, blocks, and bombs. This is a photo of Mt. Cotopaxi in Ecuador.<p><small><em>The U.S. Geological Survey</em></small></p>Shortly after 5 am on the 18<sup>th</sup> of April in 1906, most people in
  San Francisco, CA were awoken by a sudden jolt. The Earth shook violently in
  a strong <a
  href="/earth/geology/quake_1.html&edu=high&dev=">earthquake</a>.
  It lasted for only about a minute, but caused a lot of damage which destroyed
  much of the city. This photograph was taken just after an earthquake and
  fires had ravaged the city.<p><small><em>                                                    National Archives Still Picture Records Section, Special Media Archives</em></small></p>Sinkholes are <a href="/teacher_resources/main/frameworks/esl_bi8.html&edu=high&dev=">natural hazards</a> in many places around the world. They are formed when water dissolves underlying <a href="/earth/Water/carbonates.html&edu=high&dev=">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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