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The structure of Earth can be defined in two ways: by mechanical properties such as rheology, or chemically. Mechanically, it can be divided into lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core. Chemically, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core. [6]
The tectonic plates of the lithosphere on Earth Earth cutaway from center to surface, the lithosphere comprising the crust and lithospheric mantle (detail not to scale). A lithosphere (from Ancient Greek λίθος (líthos) ' rocky ' and σφαίρα (sphaíra) ' sphere ') is the rigid, [1] outermost rocky shell of a terrestrial planet or natural satellite.
The lithosphere–asthenosphere boundary (referred to as the LAB by geophysicists) represents a mechanical difference between layers in Earth's inner structure. Earth's inner structure can be described both chemically ( crust , mantle , and core ) and mechanically.
The outer layers of Earth are divided into the lithosphere and asthenosphere. The division is based on differences in mechanical properties and in the method for the transfer of heat. The lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily.
Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere , a solidified division of Earth 's layers that includes the crust and the upper part of the mantle . [ 1 ]
Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 10 24 kg (8.84 × 10 24 lb) and makes up 67% of the mass of Earth. [ 1 ] It has a thickness of 2,900 kilometers (1,800 mi) [ 1 ] making up about 46% of Earth's radius and 84% of Earth's volume.
A second low-velocity zone (not generally referred to as the LVZ, but as ULVZ) has been detected in a thin ≈50 km layer at the core-mantle boundary. [3] These LVZs may have important implications for plate tectonics and the origin of the Earth's crust. [2] [3] [4]
The lithosphere layer is composed of two parts, an upper, the crustal lithosphere and lower, the mantle lithosphere. The crustal lithosphere is in unstable mechanical equilibrium because the underlying mantle lithosphere has a greater density than the asthenosphere below. [ 1 ]