1 Physical characteristics
Main article: Geology
1.1 Structure
The interior of Earth, like that of the other terrestrial planets, is chemically divided into an outer siliceousSilicon is the chemical element in the periodic table that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. It is the second most abundant element in the Earth's crust, making up 25 solid crustIn geology, a crust is the outer layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than that of its deeper layers. On partially-molten planets, such as Earth, the lithosphere is floating on fluid, a highly viscous mantleThe mantle is the layer in the structure of the Earth that lies directly under the Earth's crust. It lies between 30 and 2,900 km below the surface. The boundary between the crust and the mantle is the Mohorovicic discontinuity, named for its discoverer,, 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 fieldA magnetosphere is the region around an astronomical object, in which phenomena are dominated by its magnetic field. Earth is surrounded by a magnetosphere, as are the magnetized planets Jupiter, Saturn, Uranus and Neptune. Mercury is magnetized, but too due to the convection of its electrically conductive material.
New material constantly finds its way to the surface through volcanoes and cracks in the ocean floors (see seafloor spreadingSeafloor spreading is a part of the theory of plate tectonics. Sea floor spreading is the process by which continental drift occurs. This phenomenon is known to be caused by convection currents in the plastic, semi-molten upper mantle, or asthenosphere.). Much of Earth's crust is less than 100 million (1×108) years old; the very oldest parts of the crust are as much as 4.4 billion (4.4×109) years old [1].
Taken as a whole, Earth's composition by mass is:
- 34.6% IronThis article is about metallic iron. For the ironing device, see ironing manganese iron cobalt Fe Ru Full table General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4 , d Density, Hardness 7874 kg/m3,
- 29.5% OxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un
- 15.2% SiliconSilicon is the chemical element in the periodic table that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. It is the second most abundant element in the Earth's crust, making up 25
- 12.7% MagnesiumMagnesium is the chemical element in the periodic table that has the symbol Mg and atomic number 12. Magnesium is the eighth most abundant element and constitutes about 2% of the Earth's crust, and it is the third most plentiful element dissolved in seawa
- 2.4% Nickel
- 1.9% Sulfur
- 0.05% Titanium
- 3.65% Other elements
See also gravity inside the Earth.
1.2 Interior
The interior of Earth reaches temperatures of 5270 K. 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.
- 0-60 km - Lithosphere
- 30/35-2900 km - Mantle
- 2900-5100 km - Outer Core
- 5100-~6375 km - Inner Core
