@holvek: The internal structure of Earth is a complex, differentiated system of concentric layers, classified chemically into the crust, mantle, and core, and mechanically into the lithosphere, asthenosphere, mesosphere, and core components. Our planet formed approximately 4.5 billion years ago, and during the process of gravitational differentiation, the heaviest elements (iron and nickel) sank to the center to form a scorching metallic core, while lighter silicate and aluminosilicate compounds rose to the surface, solidifying into a rigid outer shell. Because humanity has only managed to physically drill a record 12,262 meters (40,230 feet) deep into the ground via the Kola Superdeep Borehole — amounting to less than 0.2% of Earth's total radius — all fundamental knowledge about these geospheres has been gathered indirectly, primarily through seismic tomography, which analyzes the speed, reflection, and refraction of longitudinal ($P$) and transverse ($S$) waves from earthquakes at structural boundaries like the Mohorovičić discontinuity (between the crust and mantle) and the Gutenberg discontinuity (between the mantle and core). The topmost and thinnest layer of the planet is the Earth's crust, which exists in two distinct types: continental crust (35 to 70 km thick, composed of sedimentary, granitic, and basaltic rock layers) and the younger, denser oceanic crust (only 5 to 10 km thick, lacking a granitic layer and composed mainly of basalt and gabbro). Together with the uppermost brittle section of the mantle, the crust forms the lithosphere — the rigid, fractured outer shell of Earth broken into massive tectonic plates that float and slowly drift over a semi-fluid, ductile layer of the upper mantle known as the asthenosphere. Beneath this, extending down to a depth of 2,900 kilometers, lies the lower mantle (mesosphere), made of magnesium- and iron-rich silicates like bridgmanite; despite temperatures soaring up to 4,000 °C, intense pressure keeps these rocks solid, though they still undergo ultra-slow thermal convection that acts as the primary engine driving plate tectonics, volcanism, and mountain building. At the very heart of the planet lies a giant core with a radius of about 3,480 km, split into two contrasting zones: the outer core, roughly 2,200 km thick, is completely liquid, and it is the convective churning of this electrically conductive iron-nickel melt that generates Earth's global geomagnetic field via the dynamo effect, whereas the inner core, with a radius of about 1,220 km, remains completely solid due to a crushing pressure of 3.5 million atmospheres despite being heated to 6,000 °C — a temperature matching the surface of the Sun, sustained by primordial heat and the radioactive decay of unstable isotopes. #earth #fact #sciencetok #physicstok

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Friday 04 September 2026 09:20:18 GMT