<P> Two main zones are distinguished in the upper mantle : the inner asthenosphere composed of plastic flowing rock of varying thickness , on average about 200 km ( 120 mi ) thick , and the lowermost part of the lithosphere composed of rigid rock about 50 to 120 km ( 31 to 75 mi ) thick . A thin crust , the upper part of the lithosphere , surrounds the mantle and is about 5 to 75 km ( 3.1 to 46.6 mi ) thick . Recent analysis of hydrous ringwoodite from the mantle suggests that there is between one and three times as much water in the transition zone between the lower and upper mantle than in all the world 's oceans combined . </P>
<P> Two main zones are distinguished in the upper mantle : the inner asthenosphere composed of plastic flowing rock of varying thickness , on average about 200 km ( 120 mi ) thick , and the lowermost part of the lithosphere composed of rigid rock about 50 to 120 km ( 31 to 75 mi ) thick . A thin crust , the upper part of the lithosphere , surrounds the mantle and is about 5 to 75 km ( 3.1 to 46.6 mi ) thick . Recent analysis of hydrous ringwoodite from the mantle suggests that there is between one and three times as much water in the transition zone between the lower and upper mantle than in all the world 's oceans combined . </P>
the upper mantle below the earth 's crust is known as the
the upper mantle below the earth 's crust is known as the
asthenosphere
asthenosphere