the upper mantle below the earth's crust is known as the
Mantle (geology) 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,[16] and the lowermost part of the lithosphere composed of rigid rock about 50 to 120 km (31 to 75 mi) thick.[17] 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.[18] Recent analysis of hydrous ringwoodite from the mantle suggests that there is between one[19] and three[20] times as much water in the transition zone between the lower and upper mantle than in all the world's oceans combined.[21]