<P> A lithosphere (Ancient Greek: λίθος (lithos) for "rocky", and σφαίρα (sphaira) for "sphere") is the rigid, outermost shell of a terrestrial - type planet or natural satellite that is defined by its rigid mechanical properties . On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater . The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy . </P> <P> Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth . The lithosphere is subdivided into tectonic plates . The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere . The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle . The Lithosphere - Asthenosphere boundary is defined by a difference in response to stress: the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation . The study of past and current formations of landscapes is called geomorphology . </P>

What is the meaning of lithosphere in science
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