What is the Lithosphere?
The lithosphere, Greek for “rocky sphere,” is the outermost shell of the Earth. The term is also used to refer to the outermost rocky shell of other solid planets. It is a relatively thin layer, 50-100 km thick under the oceans, 150 km thick on the continents. The lithosphere is composed of the upper crust, 5 km thick in the oceans and 65 km thick on the continents, and the upper mantle, which makes up the remainder. Separating the crust and the upper mantle is the Mohorovičić discontinuity, the point at which rocks become plastic rather than solid. Beneath the lithosphere is the asthenosphere, which continues the upper mantle, and is approximately the point at which the mantle becomes liquid. The lithosphere consists of lithospheric plates, otherwise known as the tectonic plates, which drift slowly over time periods of millions of years. The rate of drift of these plates is comparable to the rate at which your fingernails grow. Over long periods of time, however, they can create might
Lithosphere = rock sphere Having the properties of rock The layer with strength (cf. Asthenosphere = weak sphere) Defined by Joseph Barell in a series of papers all under the same title, “The Strength of the Earth’s Crust,” and published over a period of a year and a half in 1914-15: Journal of Geology, vol. 22, 1914, pp. 28-48, 145-165, 209-236, 289-314, 441-468, 537-555, 655-683, 729-741. Journal of Geology, vol. 23, 1915, pp. 27-44, 425-443, 499-515. Quotations from Barell (my emphasis): “The zone of compensation, being competent to sustain stresses imposed by the topography and its isostatic compensation must obey the laws pertaining to the elasticity of the solid state and is to be regarded therefore as of the nature of rock. Consequently there may be extended to all of it the name of lithosphere, even though it included from time to time molten bodies, the constituents of the pyrosphere.” The theory of isostasy shows that below the lithosphere there exists in contradistinction a
