Earth's Interior

Earth formed like any other planetary body in the solar system by accretion of planetesimals, heating and differentiation. Due to impacts, radioactivity or tidal gravitational effects, a part of primitive Earth's material melted and that material differentiated into three layers due to density differences: heavier material sank to planet's center forming a planet core, lighter material (mostly basalt and silicates) formed what is called a "mantle", as lightest material floated atop and cooled, forming a thin crust. Hence Earth has a layered structure: a core, a mantle and a crust. Earth has a diameter of 7,900 mi (12,750 km)

click to a view of Earth's interior

• core of the Earth is the densest part of Earth as it is mostly metallic (iron-nickel alloy). It parts into a solid inner core, and an outer liquid core. Inner core has a temperature of 7,800° F (4,300° C) and a radius of 795 mi (1,278 km). It is solid because of the pression existing at Earth's center. It is mostly made of iron. Outer core is 1,370 mi (2,200 km) wide, has a temperature of 6,700° F (3,700° C), is liquid iron and 10 percent sulfur. It's the liquid outer core rotation about inner core which yields Earth's magnetic field. This works like a dynamo
• mantle is a dense, hot layer of semi-molten rock. It is about mi 2,100 mi (3,400 km) thick. It contains iron, magnesium, calcium, silicon, and oxygen. Mantle is plastic as temperature and pression are high at his depth
• crust is the outermost, thin layer of Earth. Its thickness varies from 3 mi (5 km) under the oceans, to about 19 mi (30 km) at the continents. It may reach up to 62 mi (100 km) under the large mountain ranges. There crust goes deeper. It is rich in oxygen and silicon with lesser amounts of miscellaneous materials like aluminum, iron, magnesium, calcium, potassium, or sodium. Oceanic crust is made of basalt as continental crust is made of lower density rocks like andesite or granite

This model is further complicated as the uppermost, cooler, part of the mantle is somehow jointed to the crust which is just above it and they behave similarly. Together they are forming the "lithosphere" ("lithos" in Greek means "rock"), which is 50 mi (80 km) thick in average. The lithosphere has been broken into the plates plate tectonics is about. The next layer of the mantle forms the "asthenosphere" ("astenos" in Greek means "weak"). The asthenosphere is found just beneath the lithosphere. It's a narrow, mobile zone made of hot, semi-solid material which can soften and flow after subjected to high temperature and pressure over geologic time. It's the various motions of this system which yields the plate tectonics; asthenosphere is slowly moving. The more rigid lithosphere is floating above, or about it