text: The Earth's structure is the geologic and atmospheric structure of earth.\nContents\n[hide]\n\n    * 1 Shape\n    * 2 Structure\n    * 3 Interior\n          o 3.1 Interior heat\n          o 3.2 Structure\n    * 4 The core\n    * 5 Mantle\n    * 6 The Crust\n    * 7 Hydrosphere\n    * 8 Atmosphere\n    * 9 Historical development and alternative conceptions\n    * 10 See also\n\n[edit]\n\nShape\n\nThe Earth's shape is that of an oblate spheroid, with an average diameter of approximately 12,742 km. The rotation of the Earth causes the equator to bulge out slightly so that the equatorial diameter is 43 km larger than the pole to pole diameter. The largest local deviations in the rocky surface of the Earth are Mount Everest (8,850 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Hence compared to a perfect ellipsoid, the Earth has a tolerance of about one part in about 584, or 0.17%. For perspective, this is a bit more than the 0.05% tolerance allowed in billiard balls. Due to the bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador. The mass of the Earth is approximately 5980 yottagrams (5.98 x 1024 kg).\n[edit]\n\nStructure\n\nThe interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The liquid outer core gives rise to a weak magnetic field due to the convection of its electrically conductive material.\n\nNew material constantly finds its way to the surface through volcanoes and cracks in the ocean floors (see seafloor spreading). Many of the rocks now making up the Earth's crust formed less than 100 million (1×108) years ago; however the oldest known mineral grains are 4.4 billion (4.4×109) years old, indicating that the Earth has had a solid crust for at least that long [1].\n\nTaken as a whole, the Earth's composition by mass [2] is:\n\n    iron: 35 .1 %\n    oxygen: 28 .2 %\n    silicon: 17 .2 %\n    magnesium: 15 .9 %\n    nickel: 1 .6 %\n    calcium: 1 .6 %\n    aluminium: 1 .5 %\n    sulfur: 0 .70 %\n    sodium: 0 .25 %\n    titanium: 0 .071 %\n    potassium: 0 .019  %\n    other elements:     0 .53 %\n\nInterior heat\n\n    Main article: geothermal (geology)\n\nThe interior of the Earth reaches temperatures of 5650 ± 600 kelvins [3] [4]. The planet's internal heat was originally generated during its accretion (see gravitational binding energy), and since then additional heat has continued to be generated by the decay of radioactive elements such as uranium, thorium, and potassium. The heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the Sun.\n[edit]\n\nStructure\n\nEarth's composition (by depth below surface):\n\n    * 0 to 60 km - Lithosphere (locally varies 5-200 km)\n          o 0 to 35 km - Crust (locally varies 5-70 km)\n          o 35 to 60 km - Uppermost part of mantle\n    * 35 to 2890 km - Mantle\n          o 100 to 700 km - Asthenosphere\n    * 2890 to 5100 km - Outer Core\n    * 5100 to 6378 km - Inner Core\n\n[edit]\n\nThe core\n\nThe average density of the Earth is 5515 kg/m3, making it the densest planet in the Solar system. Since the average density of surface material is only around 3000 kg/m3, we must conclude that denser materials exist within the core of the Earth. Further evidence for the high density core comes from the study of seismology. Since iron is the heaviest element that can be created by a star's fusion, the core of the earth and the other planets must be iron. All heavier elements are rare or trace. In its earliest stages, about 4.5 billion (4.5×109) years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation, while less-dense materials would have migrated to the crust.