Lithosphere-Asthenosphere boundary found to become deeper under older crust, thus supporting the suggestion that the discontinuity is closely interrelated to the LAB. Beneath oceanic crust, the LAB ranges anywhere from 50 to 140 km in depth except at mid-ocean ridges where the LAB is no deeper than the depth of the new crust being created. Seismic evidence shows that oceanic plates do thicken with age. This would suggest that the Lithosphere-Asthenosphere boundary underneath oceanic lithosphere also deepens with plate age. Data from ocean seismometers indicate a sharp age-dependent LAB beneath the Pacific and Philippine plates and has been interpreted as evidence for
Lithosphere felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convection in the mantle. The thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. Here, formula_2 is the thickness of the oceanic mantle lithosphere, formula_3 is the thermal diffusivity (approximately 10 m/s)